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Tuberculosis in the Workplace (2001)

Chapter: Appendix C The Occupational Tuberculosis Risk of Health Care Workers

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Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

C
The Occupational Tuberculosis Risk of Health Care Workers

Thomas M.Daniel, M.D.*

SUMMARY AND CONCLUSIONS

A review of published literature has been undertaken in response to a commission from the Institute of Medicine Committee on Regulating Occupational Exposure to Tuberculosis. The charge of this commission was to prepare a review paper addressing the question of whether health care workers (and workers at other sites covered by the proposed regulations of the Occupational Safety and Health Administration [OSHA]) are at a greater risk of infection, disease, and mortality due to tuberculosis than the general community within which they reside. This paper focuses principally on the risk of infection, with only limited comments on the risks of disease and mortality. In conducting this review, the author faced limitations imposed by the quality of the published data and by the lack of published information relevant to some of the aspects of the charge. In particular, much of the quantitative data presented here can be taken as no more than approximate. Nevertheless, certain conclusions have been drawn by the author.

Health care workers are at risk of contracting tuberculous infection in the workplace. This risk has been declining in recent decades. In those health care facilities where modern infection control measures are in place, it now approaches the level of risk incurred by health care workers in the communities in which they reside. That it has declined and continues to

*  

Professor Emeritus of Medicine and International Health, Case Western Reserve University, Cleveland, Ohio.

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

decline means that it has been higher than the baseline community risk, and it will not be possible to assume that there is no excess risk until no further decline is observed.

A large portion of the current and recent risk to health care workers of tuberculous infection is the result of exposure to unsuspected cases of infectious tuberculosis or to exposure in circumstances of poor ventilation. In some outbreaks from unsuspected sources, exposed employee infection rates have been as high as 50 percent. When effective infection control procedures are in place, unsuspected contagious cases of tuberculosis may provide nearly all of the occupational tuberculosis risk.

The risk to health care workers of tuberculous infection varies with job category. In general, health care workers in contact with patients are at higher risk than those with no patient contact. Noncontact employees often have a higher incidence of infection than contact employees, but this is due to community exposure risk. Job situations of exceptionally high risk are those involving the generation of respiratory aerosols from patients, including bronchoscopy, endotracheal suctioning and intubation, cough and sputum induction, and the administration of irritation medications (e.g., pentamidine) by aerosol.

The risk to health care workers of tuberculous infection varies in the United States with geographic locale. The incidence of tuberculosis varies greatly with location in the United States. Coastal urban cities bear the greatest tuberculosis burden and rural Midwest and mountain state regions the least. Health care facilities in these various regions care for numbers of patients with tuberculosis that vary substantially in parallel with variations in incidence.

The risk to health care workers of tuberculous infection varies in the United States with demography and ethnicity. In general, individuals of African-American, Hispanic, and Asian heritage have a higher incidence of tuberculous infection than do persons of European extraction. Foreign-born Americans bring with them much of the tuberculous infection risk of the countries of their origins. The risk of tuberculous infection varies greatly with socioeconomic status, most of the infection risk being incurred by those who are less affluent. For health care workers, these variations in population tuberculosis incidence have two important consequences. First of all, the tuberculous infection risk in the community in which health care workers reside and in which they usually spend more time than they do in their job setting is correlated with these ethnic and demographic variables. Second, the population served by the health care facility will influence the amount of potential tuberculosis exposure of the employees.

The occupational tuberculosis risk to American health care workers can be quantified only in approximate terms. The magnitude of the tuberculosis risk to American health care workers at the current time in those

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

facilities where recent Centers for Disease Control and Prevention (CDC) guidelines for infection control have been implemented is usually not substantially greater than the risk incurred by these individuals in the communities in which they reside.

The risk to infected health care workers of progression to tuberculous disease (tuberculosis) is lower than often stated; the risk of mortality for immunocompetent individuals harboring drug-susceptible organisms is negligible. The risks of tuberculous disease and mortality in Mycobacterium tuberculosis-infected health care workers is probably no higher than that of individuals in the general population. Overall, the risk of tuberculosis in individuals who become infected as adults is probably of the order of 5 percent. Nearly all of the tuberculosis mortality in the United States today is accounted for by individuals who fail to be diagnosed or treated in timely fashion, who are immunocompromised (usually by human immunodeficiency virus [HIV] infection), or who suffer from multidrug-resistant tuberculosis.

INTRODUCTION

In an era of recently resurgent tuberculosis and accompanying concern about the occupational tuberculosis risk of health care workers, the Institute of Medicine has been asked by the U.S. Congress to study the magnitude of this occupational risk and the potential impact on it of a newly proposed rule regulating the environment in which care of tuberculosis patients is conducted. At the present time, health care workers account for about 3 percent of the cases of tuberculosis reported in the United States (1).

Charge to the Reviewer

This paper reviews the published medical literature relevant to the occupational tuberculosis risks of American health care workers. It was commissioned by the Institute of Medicine Committee on Regulating Occupational Exposure to Tuberculosis. The charge of this committee was to prepare a state-of-the-art literature review addressing the following questions:

Are health care workers (and workers at other sites covered by the proposed OSHA regulations) at a greater risk of infection, disease, and mortality due to tuberculosis than the general community within which they reside? If so, what is the excess risk due to occupational exposure? Can the occupationally acquired risk be quantified for different work environments and different job classifications?

Determinants of Tuberculosis Risks

Consideration of the occupational tuberculosis risk of health care workers must be done in two parts: the risk of infection and the risk of

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

disease. The determinants of these risks are multiple. Exposure is a major determinant of infection risk, and it may be related to the work place, although it must be realized that health care workers may also face exposure in the communities in which they reside. Individual factors such as age, immune status, and genetic composition (possibly including race) are also important, especially for the risk of disease. These factors are not per se related to the workplace, but that does not mean they are not operative in the workplace.

Published Literature Reviews

There have been a number of well-done literature reviews of the occupational tuberculosis risk to health care workers published during the past decade (29). In general, these reviews emphasize the risk of tuberculous infection and do not deal with the subsequent risk of disease. Nor do they provide much information permitting one to compare the workplace risk to that incurred in the community in which health care workers reside. These reviews have documented that tuberculin conversion rates for American health care workers in the recent past were as high as 4–5 percent/year in many urban areas and perhaps twice that in some areas of New York City and for certain job situations with high exposures to aerosols of respiratory secretions. In nonurban areas, they were generally lower than 0.2 percent/year. With the implementation of enhanced infection control measures recommended by such advisory groups as CDC during the past decade, these rates have dropped to below 1 percent generally. However, outbreaks continue to occur from unrecognized sources, and with these outbreaks the tuberculin conversion rates among exposed employees may be as high as 50 percent.

METHODS

Literature Review

This paper is based on a review of published literature. Searching was done using PubMed (MedLine) with a variety of topics relevant to tuberculosis and health care workers. Additional publications were selected from the bibliographies of published reports. Identified papers were then retrieved using the resources of the Health Sciences Library and Allen Memorial Library of Case Western Reserve University. Finally, a number of relevant papers were already present in the author’s personal library and reprint collection.

Data presented in this paper have been converted, when possible, from the form in which they were originally presented to percent per year. In a few reports, the original data are given as per 100 person-years, and this

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

more precise form has been retained. In many instances, no time interval was given, and in these cases percent is used. Because many of these conversions to percentages are based on small absolute numbers, the actual numbers are given in those cases to allow the reader to note this fact.

Annual Risk of Tuberculous Infection

The annual risk of infection (ARI) with M. tuberculosis, the tubercle bacillus, is central to any consideration of the occupational tuberculosis risk of health care workers. Ideally, one would like to know this figure not only for employees but also for the community in which they reside. Data upon which the ARI for American populations can be calculated are generally lacking, however, and many of the reports of infections in health care workers do not provide relevant time intervals. In this review, ARI is expressed as percent per year, the usage of most workers who have dealt with this subject.

It is acknowledged that the term “annual risk” as it is used here is imprecise—annual probability or likelihood would be more accurate terms—but its use is widely established in the published literature on this subject, and it is used here for consistency with that literature. It is also true that such calculations on an annual basis ignore the fact that the pool of individuals considered may change during a year. However, data are almost always lacking in the studies reviewed here for estimation of the more accurate use of person-years at risk. Errors thus introduced are small at low levels of risk and do not affect the conclusions drawn in this review.

Two types of ARI are reported here: (a) calculated annual risks, when the data permit such direct calculation, and (b) estimated annual risks based on tuberculosis incidence when direct calculation is not possible.

Calculated Annual Risk of Infection

If one accepts the development of tuberculin hypersensitivity as a reliable index of primary tuberculous infection, then it is a straightforward task to calculate the ARI with M. tuberculosis expressed as percent per year from serial skin testing data. The algebraic formula for this calculation is

ARI = [1 − (Qb/Qa)1/(b−a)] * 100,

where Q is 1 − P, P is the probability of being infected at a given age or year a or b, a is the initial age or year of observation, and b is the second year or age of observation (10). In the text of the present review paper, ARI thus calculated is referred to as the “calculated ARI.”

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×
Estimated Annual Risk of Infection

Styblo has observed that there is an empiric and relatively constant relationship between the incidence of smear-positive tuberculosis and the annual risk of infection (11). He estimated that the ratio between this incidence and the ARI ranged between 50 and 60 in a variety of populations, pricipally those of high tuberculosis prevalence. Daniel and Debanne reasoned that this relationship could be used in reverse to estimate ARI when good case reporting was available but tuberculin skin test data were absent. They tested this hypothesis using data from white male U.S. naval recruits and found that in this population the ratio of incidence of tuberculosis of all forms to ARI was approximately 150 (10). The disparity between this figure and the lower figure of Styblo may result in part from the use of low-incidence populations, but the largest reason for the difference rests with the use by Daniel and Debanne of rates for all forms of tuberculosis, whereas Styblo considered only single-sputum smear-positive, pulmonary tuberculosis. In the current review paper estimation of ARIs is based on a ratio of 150, and ARI thus derived is referred to as the “estimated ARI.” While this method is imprecise, it is often the only means available to judge ARI in American populations.

Limitations of This Study

In doing this review, three limitations were deliberately imposed. First, papers published prior to 1970 were used only to a limited degree and then only to provide historical context. Second, limited use was made of reports of outbreaks, for these accounts are usually anecdotal in character. Third, most papers describing studies done in other countries were excluded because both health care occupational sites and attitudes toward occupational risks in most other countries differ substantially from those in the United States.

A major limitation in this review and in the entire body of knowledge that it approaches rests with the definitions of tuberculous infection and of tuberculous disease. This subject is separately addressed in a paper authored by John B. Bass Jr., and is included in this report as Appendix B.

RISK OF TUBERCULOUS INFECTION

Risk in the U.S. General Population

If one is to examine the occupational risk of tuberculous infection among health care workers in relation to the communities in which they reside, then it is first important to try to determine the annual risk of infection in the general American public. Tuberculin testing data upon

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

which such a determination can be based are limited. The last systematic attempt to estimate the prevalence of tuberculin reactivity in the United States was that of the National Health Survey of 1971–72, which concluded that in American adults aged 25 to 74 years the prevalence of tuberculin reactivity was 21.5 percent (12). A reasonable estimate for the current date for Americans of all ages might be 5 to 10 percent, and perhaps 10 percent in adults.

Tuberculous infection is not uniformly distributed among Americans, and it is important to stratify any assessment of the general population risk so that infection in health care workers can be compared with that in the appropriate reference community. For example, tuberculosis is much more common in urban areas than in rural areas, and even in the cities of middle America it is not as frequent as in this country’s coastal cities. Many demographic factors correlate with tuberculosis incidence in America. Health care workers are employed, while nearly 60 percent of tuberculosis in the United States occurs among the unemployed (1). Importantly for this consideration, a substantial number of health care workers are foreign-born, one-third of them coming from the Philippines; among other employed persons, one-quarter come from Mexico (A. Curtis, personal communication of material presented to a workshop held in December 1999). The importance of this difference rests with the difference in tuberculosis in the countries of origin for these groups. Based on recent World Health Organization estimates, the current incidence of sputum smear-positive tuberculosis in the Philippines is 260/100,000, and that in Mexico is 58/100,000 (13).

Calculated ARI with M. tuberculosis in Selected American Populations

There are relatively few tuberculin surveys available from which one can calculate the ARI in American populations and none in recent years. Moreover, those surveys that have been conducted have often been flawed by the use of poorly standardized tuberculin testing techniques and by poor characterization of the populations studied, especially with respect to demographic characteristics. The use of tuberculins other than purified protein derivative (PPD) at 5 tuberculin units may lead to an overestimation of the actual prevalence of tuberculin reactivity. Data from 12 selected surveys conducted in the United States during the middle half of the 1990s are presented in Table C-1. These studies rarely involved serial testing or testing of more than one age group. In that situation, the calculation of ARI for Table C-1 was done from birth, assuming a reactor rate of zero at birth, a maneuver admittedly flawed because it assumes the risk to be uniform throughout life. The error thus introduced has the potential for underestimating the adult risk relevant to health care workers.

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

TABLE C-1. Tuberculin Surveys in the United States and ARI with M. tuberculosis Calculated from Them

Year of Study

Population (Reference)

Tuberculin*

Calculated ARI (%/year)

1930

New York City, schoolchildren (17)

OT, 10 TU

11.14

1957

Pamlico County, GA, general population (18)

PPD-S, 5 TU

0.25

1957–60

Chicago nursing students (19)

OT, 2 TU

0.75

1958–65

White naval recruits (20)

PPD-S, 5 TU

0.14

1963

Pennsylvania high school students (21)

PPD, 5 TU

0.19

1964–65

Air force recruits (14)

Tine test

0.16

1965–69

First grade children in United States (21)

Probably PPD-S

0.08–0.05

1964–67

CDC surveys at selected sites (22)

PPD, 5 TU

0.16

1971–72

National health survey (HANES) (12)

PPD-S, 5 TU

0.58

1973–74

New York City Board of Education employees (16)

PPD, 5 TU

0.23

1975–79

CDC-reported data from selected sites (1)

Variable

0.20–0.15

1980–81

New York City school children (23)

PPD, 5 TU

0.45

*Tuberculins used for skin testing have included old tuberculin (OT), a crude preparation, and purified protein derivative (PPD), a somewhat purified preparation made from OT. PPD has been made by many manufacturers. PPD-S refers to a single large batch of PPD prepared by Florence Seibert, of which half was deposited as the reference standard against which all other PPDs are standardized and half was given to the U.S. Public Health Service for use in research studies. Tine tests use OT. The dose of tuberculin used for testing is expressed in tuberculin units (TU), which are based upon bioequivalent standardization with PPD-S. The usual dose, for which the largest amount of validation data are available, is 5 TU.

It is evident that ARIs are larger in urban populations—specifically, New York City—than elsewhere. Unfortunately, the available data often are not sufficient to make generalizations with respect to geography nor with respect to such demographic factors as ethnicity or socioeconomic status. Two studies of military recruits allow one to examine race and ethnicity (14, 15). The annual risks of infection calculated from these studies are shown in Table C-2. Data from a single study in New York City school board employees allow one to examine race and ethnicity in the urban setting (16). The calculated ARIs from this study are shown in Table C-3. The ARI calculated for African American and Hispanic military recruits for 1990 was approximately six times that for whites. For Asian recruits the calculated ARI was approximately 36 times that for whites. For New York City, calculation from the 1973 data yielded an ARI for African Americans 8.6 times those in whites and for Puerto Ricans 6.5 times those in whites.

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

TABLE C-2. ARIs Calculated for U.S. Military Recruits in 1965 (14) and 1990 (15)

Racial/Ethnic Group as Characterized by Study Author

Calculated ARI, 1965 (30) (%/year)

Calculated ARI, 1990 (35) (%/year)

White

0.16

0.04

Black

0.56

0.25

Puerto Rican

1.12

0.26

American Indian

0.92

 

Asian

 

1.45

TABLE C-3. ARIs Calculated for New York City in 1962 (20) and 1973 (16)

Racial/Ethnic Group as Characterized by Study Author

Calculated ARI, 1962 (20) (%/year)

Calculated ARI, 1973 (16) (%/year)

White

0.2

0.08

Black

0.69

Puerto Rican

0.52

Estimated ARI with M. Tuberculosis in Selected American Populations

As noted previously, it is possible to estimate the ARI from reported case rates. However, one must be cautious about the precision of these estimates. Having expressed this concern about their use, estimated ARIs are presented for various American populations in Tables C-4, C-5, and C-6.

TABLE C-4. ARI in 1998 Estimated by Method of Daniel and Debanne (10) for Various Demographic and Racial Segments of the U.S. Population, 25- to 44-Year-Old Age Cohort

Population Group

Tuberculosis Case Rate per 100,000, 1998*

Estimated ARI (%/year)

United States total

6.8

0.05

White, not Hispanic, male

3.1

0.02

White, not Hispanic, female

1.5

0.01

Black, not Hispanic, male

23.5

0.16

Black, not Hispanic, female

12.7

0.08

Hispanic male

17.1

0.11

Hispanic female

9.9

0.07

Asian/Pacific Islander, male

42.8

0.29

Asian/Pacific Islander, female

30.9

0.21

*Tuberculosis case rates for 1998 are CDC-reported data (1).

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

TABLE C-5. ARI in 1998 Estimated by Method of Daniel and Debanne (10) for Selected American Cities, All Ages

City

Tuberculosis Case Rate per 100,000, 1998*

Estimated ARI (%/year)

Atlanta, GA

8.9

0.06

Baltimore, MD

7.6

0.05

Greensboro, NC

5.6

0.04

Los Angeles, CA

14.9

0.10

Miami, FL

13.4

0.09

New York, NY

19.1

0.13

Newark, NJ

10.7

0.07

Philadelphia, PA

5.8

0.04

St. Louis, MO

4.3

0.03

Salt Lake City, UT

3.3

0.02

San Francisco, CA

18.2

0.12

Seattle, WA

5.9

0.04

*Tuberculosis case rates for 1998 are CDC-reported data (1).

Summary of Risk of Tuberculous Infection in the General U.S. Population

In general, the ARI in American populations has been declining during the past century and is now very low, although it may have increased in New York City and certain other urban areas with the recent resurgence of tuberculosis. The risk is much lower in rural areas and cities in the Midwest and mountain states than it is in major coastal cities, where most of the infectious cases of tuberculosis occur. The risk in America’s

TABLE C-6. ARI Estimated by Method of Daniel and Debanne (10) for Selected Demographic Groups Ages 16–64 Years as Reported for 1984– 85 by McKenna and Colleagues (24)

Demographic Group

Tuberculosis Case Rate per 100,000

Estimated ARI (%/year)

Total

8.4

0.06

Not Hispanic, white

3.6

0.02

Not Hispanic, black

35.1

0.23

Hispanic

20.2

0.13

Asian

56.1

0.37

Male

11.8

0.08

Female

5.1

0.03

Currently employed

4.9

0.03

Previously employed

11.6

0.08

Unemployed

337.2

2.25

U.S.-born

7.2

0.05

Foreign-born

29.2

0.19

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

ethnic minority populations is much higher than it is in Americans of European extraction—of the order of 0.1 to 0.2 percent/year as opposed to 0.01 to 0.02 percent/year. For unemployed individuals, the group from which more than half of American tuberculosis cases are reported, the annual risk of infection probably exceeds 2.0 percent/year. Tuberculosis among foreign-born individuals now accounts for about 40 percent of new cases each year in the United States. Foreign-born individuals bring with them their infection histories from the countries in which they originate, many of them high-tuberculosis-incidence countries. The ARI in foreign-born persons in the United States is probably about 0.2 percent/ year. Considering the country as a whole, 0.05 percent is probably a reasonable estimate of the ARI.

Risk in Hospital-Based Health Care Workers

Until the 1950s, when effective chemotherapy heralded the closing of most tuberculosis sanatoria and categorical tuberculosis hospital services, the occupational risk of tuberculous infection was generally accepted by all health care workers. Indeed, primary tuberculous infection was welcomed by many because of the immunity to subsequent infection that accompanied it. Numerous studies showed student nurses to be at especially high risk, and medical students fared little better.

Following the widespread introduction of isoniazid in 1953, tuberculosis sanatoria saw a dramatic fall in their patient censuses, with much shortened hospital stays, and they began to close their doors. The May 1969 issue of the Bulletin of the National Tuberculosis and Respiratory Disease Association announced on its cover and above the first page of every article it contained, “The General Hospital is the logical place” (25). The contents of this publication are largely devoted to reassuring health care workers that there is little risk to them, although it stated that “good ventilation without recirculation of air is essential for rooms or wards used for tuberculous patients.” Unfortunately, such ventilation was not widely available in many hospitals at that time.

During the 1970s and 1980s, the decades following these changes in the venue of care of tuberculous patients, a number of outbreaks of tuberculous infection among health care workers were reported and the first attempts at systematic study of nosocomial transmission of tuberculous infection were undertaken. Most of these studies are not relevant to the current situation, but a few are worth noting because their conclusions remain important.

In 1975, Ruben, Norden, and Schuster evaluated the tuberculosis screening program for employees of a Pittsburgh hospital (26). This study is of particular note because it was among the first to look at patient contact in relation to infection. Employees considered to work in patient

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

contact had a tuberculin test conversion rate of 3.2 percent; employees working in noncontact jobs had a conversion rate of 7.8 percent. Thus, nonhospital sources of infection were considered to be more likely than hospital sources for the acquisition of infection.

In contrast with the high infection rates in the Pittsburgh experience, Vogeler and Burke found that an annual tuberculin testing program among the employees of a hospital in Salt Lake City discovered only seven converters among 2,900 to 3,400 employees tested in each year between 1972 and 1977 (27). During the 5-year period, converter rates ranged from zero to 0.49 percent/year, with an overall rate of 0.11 percent. This study illustrated the geographic variability of the risk of tuberculous infection for health care workers. The Pittsburgh hospital admitted approximately 30 to 40 cases of tuberculosis annually during the study period; the Salt Lake City hospital admitted 9 or 10.

Berman and colleagues studied tuberculin skin test conversions among the employees of a hospital in Baltimore during a 5-year period from 1971 to 1976 (28). During that time, 58 patients had cultures positive for M. tuberculosis; an unknown number of patients with negative cultures or for whom no cultures were done may have also been hospitalized. The results of this illuminating study are summarized by job category and demography in Table C-7. It is apparent that the risk of infection was much greater in maintenance, engineering, housekeeping, and laundry employees than in nursing employees. It is also apparent that risk of infection correlated strongly with race and economic status. These observations led to the conclusion that the source of tuberculous infection for most of the employees who converted their tuberculin skin tests was in the communities in which they resided rather than in the hospital.

Aitken, Anderson, and Albert conducted a prospective study of tuberculin skin test conversions among employees at all 114 hospitals in the

TABLE C-7. Tuberculin Skin Test Conversions and Calculated ARI for Employees of a Baltimore Hospital, 1971–1976 (28)

Job or Demographic Category

Number Tested

Converters

Percent

ARI (percent/year)

Nursing

733

36

4.9

.98

Maintenance, engineering, housekeeping

231

34

14.7

3.13

Laundry

32

11

34.4

8.08

Pathology

105

3

2.9

0.58

Radiology

86

2

2.3

0.47

White

1,045

38

3.6

0.74

Nonwhite

759

96

12.7

2.67

Highest economic quintile

645

36

5.6

1.14

Lowest economic quintile

151

24

15.9

3.40

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

state of Washington from January 1982 through December 1984 (29). During these 3 years the tuberculosis incidence in Washington was 7.1/ 100,000 in 1982, 5.6/100,000 in 1983, and 4.8/100,000 in 1984; national case rates for these years were 11.0/100,000 in 1982, 10.2/100,000 in 1983, and 9.4/100,000 in 1984 (1). In this survey 124,869 skin tests were completed and 110 skin test conversions were documented (excluding 19 additional converters identified by health department contact investigations). Overall, the conversion rate was 0.09 percent (calculated ARI = 0.03 percent/ year). For hospitals with no cases of tuberculosis admitted during the study interval the rate was 0.07 percent (calculated ARI = 0.02 percent/ year), and for hospitals to which cases of tuberculosis were admitted the rate was 0.091 percent (calculated ARI = 0.03 percent/year) in those hospitals with sputum smear-positive cases and 0.094 percent (calculated ARI = 0.03 percent/year) for those with smear-negative, culture-positive cases. In larger urban hospitals the rate was 0.11 percent (calculated ARI = 0.04 percent/year) and for small hospitals the rate was 0.08 percent (calculated ARI = 0.03 percent/year). There were no significant differences among these rates. The authors estimated that the tuberculin test conversion rate in the general population of Washington at that time was between 0.008 and 0.11 percent/year. They concluded that hospital employees were at no greater risk than the general public.

From these studies certain generalizations can be made about occupational tuberculosis in the 1970s and 1980s. First, it is evident that the risk of tuberculous infection was much greater in hospitals located in such cities as Baltimore than in those represented by Salt Lake City. This almost certainly reflected the tuberculosis incidence in those communities. Next, the evidence presented here indirectly, but not directly, implicates the communities in which health care workers resided as the major source of tuberculous infection. That does not mean that occupation-related infection did not occur; rather, it means that the risk in the community was often as great as or greater than the risk in the workplace. Finally, that risk related to employment was probably greatest for certain hazardous work activities, such as bronchoscopy and other aerosol-generating procedures.

Beginning in the mid-1980s and extending into the early to mid-1990s, the United States witnessed an unprecedented resurgence of tuberculosis. Borne on a tide of AIDS, homelessness, and immigration, tuberculosis rates increased in most major urban areas of the Northeast, southern Florida, and California, as well as along the Mexican-American border. In other areas of the country, notably the less densely populated central portions of the continental United States, tuberculosis case rates did not increase and continued to decline. In many of the areas of resurgence, this emerging epidemic was accompanied by increasing rates of drug resistance, including multidrug resistance. Public health agencies responded with a variety of measures, including well-reasoned guidelines intended

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

to decrease nosocomial tuberculous infections. Today, case rates are again falling nationally.

Recent Risk for Health Care Workers in Urban Locations of High Tuberculosis Incidence

Much of the recent information available comes from studies performed in the wake of outbreaks, and selection bias is inevitably introduced into such situations. The bias introduced by studying the problem in such a situation will tend to overstate the risk. On the other hand, the mere fact that a study is being conducted will tend to increase employee compliance with isolation procedures, thus reducing the risk. These biases must be remembered in drawing conclusions or making generalizations.

There have been two recent reports from St. Clare’s Hospital and Health Center in New York City (30,31). This hospital cares for many patients with tuberculosis and for many HIV-infected patients. It was the original focal point of an outbreak of multidrug-resistant strain W of M. tuberculosis in New York. During the period 1991 to 1994, 56 to 118 new cases of tuberculosis were diagnosed annually at that hospital (the reports do not give data on the secular trend). During the same time period, tuberculin skin test information was available for 1,303 employees, 711 of whom were initially tuberculin skin test negative. The conversion rates for these 711 employees grouped by occupation are shown in Table C-8 for the years 1991–1992 and 1993–1994. The rates in Table C-8 are expressed per 100 person-years, a reasonable approximation of the annual risk of infection expressed as percent. When adjusted for age, bacille Calmette-Guérin (BCG) vaccination status, country of birth, gender, and the tuberculosis incidence in the postal code zone of residence, the differences in occupational category remained significant in a multivariate

TABLE C-8. Tuberculin Conversion Rates Among Employees of St. Clare’s Hospital in New York City by Occupation Comparing 1991–1992 and 1993–1994 (30)

Conversion Ratea

Occupation

Total, 1991–1994

1991–1992

1993–1994

Laboratory

4.4

6.3

2.3

Physician or nurse

5.0

7.2

3.0

Social service

4.8

8.1

2.2

Housekeeping

9.2

11.7

6.7

Finance

2.5

3.0

1.9

Total

5.2

7.2

3.3

aConversion rates are expressed as number of conversions per 100 person-years.

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

analysis. When conversion rates were examined at 6-month intervals, the rate fell from 20.7 percent during the first 6 months of the 1991 observation period to 5.8 percent during the last 6 months of 1993 (31). During that time, negative-pressure isolation rooms, ultraviolet lights, and personal respirators were all introduced at St. Clare’s Hospital.

Maloney and coworkers studied the impact of enhanced infection control measures on nosocomial transmission of tuberculosis infection at the Cabrini Medical Center in New York City following an outbreak of multidrug-resistant tuberculosis at that facility in 1991 (32). Employee tuberculin rates were determined for an 18-month period prior to the institution of enhanced infection control measures and a 12-month period subsequent to the changes in infection control. The findings of their study are summarized in Table C-9, along with annual risks of infection calculated from their data. Overall, the annual risks of infection were higher in personnel working in contact with patients and, considering the small number of conversions documented in the noncontact group, were not changed by the implementation of infection control measures. However, conversion rates decreased following the infection control intervention on medical and HIV wards admitting patients with tuberculosis. This did not happen elsewhere in the hospital. In this study, there was no evidence of residence postal code clustering of employee conversions, nor were demographic or racial characteristics identified that contributed to the infection risk.

TABLE C-9. Tuberculin Conversions and Calculated ARI for Employees at Cabrini Medical Center, New York City, Before and After Interventions Made to Improve Infection Control (32)

Employee Category

Preintervention Conversions

18 months ARI (%/year)

Post-intervention Conversions

12 months ARI (%/year)

Working in patient contact

22/342 (6.4)

4.3

14/296 (4.7)

4.7

Not working in patient contact

4/409 (1.0)

0.7

8/354 (2.3)

2.3

Working on ward admitting TB patients

15/90 (16.7)

11.5

4/78 (5.1)

5.1

Working on ward not admitting tuberculosis patients

7/254 (2.8)

1.9

9/228 (4.0)

4.0

NOTE: The preintervention period included an outbreak. Note that the time intervals for the pre- and postintervention periods differ, meaning that the conversions as expressed as percentages by the authors are not directly comparable. Data from Maloney and coworkers. Conversion rates are number of skin test conversions/number of employees tested (percent).

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

Blumberg, Sotir, and colleagues studied nosocomial transmission of tuberculosis infection and skin test conversions among employees at Grady Hospital in Atlanta, Georgia, a public hospital admitting about 200 tuberculous patients annually during the first half of the 1990s before and after implementation of intensified infection control measures (33,34). Six-month conversion rates fell from 118/3,579 (3.3 percent; calculated ARI = 6.49 percent/year) in the first 6 months of 1992 to 23/5,153 (0.4 percent; calculated ARI = 0.89 percent/year) during the first 6 months of 1994. During the latter period, the conversion rate was not related to job status but was positively correlated with black race and low economic status. Subsequently, Blumberg and associates studied tuberculin skin test conversions among house staff in the Emory University Affiliated Hospitals Training Program (35). These interns and residents spend approximately half of their training time at Grady Hospital. As noted above, expanded infection control measures were implemented at Grady Hospital in 1992, and tuberculin test conversion rates were compared for the 6-month period at the initiation of these measures with the rates for the subsequent 4.5 years. The rate fell from 6.0 per 100 person-years to 1.1 per 100 person-years (p <0.001). Rates were significantly higher for house officers in medicine and obstetrics/gynecology than for those other clinical departments. Graduates of foreign medical schools had higher conversion rates than American graduates. As at St. Clare’s Hospital and the Cabrini Medical Center in New York, the implementation of control measures was thought to have had an impact on transmission of infection to the health care workers at Grady Hospital.

An important study of tuberculosis in New York City health care workers was conducted using restriction fragment length polymorphism (RFLP) DNA fingerprinting techniques (36). In 1992–1994 among six New York City hospitals where no recognized nosocomial outbreaks of tuberculosis occurred, isolates from 20 cases of tuberculosis occurring in health care workers were available for typing. Of the 20, 8 were nurses or nurses aides, 7 were physicians, and the remaining 5 were not in patient contact positions. The tuberculous health care workers from whom the fingerprinted organisms were isolated did not differ from those from 181 nonhealth care workers similarly studied with respect to age, sex, country of birth, race, and HIV infection status. The fingerprinting technique allowed the identification of clusters of patients all infected with the same strain of M. tuberculosis. Overall, 87 of 201 isolates fingerprinted in New York during the period of the study were clustered, indicating that they represented recent transmission of currently circulating strains. Among health care workers, clustered strains were found in six of the seven physicians and in eight of the nine HIV-infected workers (all occupations). This suggests that physicians and HIV-infected persons were particularly susceptible to occupational infection.

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

In a single tuberculin test survey of 91 patient transport and housekeeping hospital employees in Philadelphia, patient contact was not related to tuberculin skin test positivity (37). Foreign birth was, with a relative risk of 0.4 (U.S. birth to foreign birth) for employees with patient contact and 0.8 for employees without patient contact.

At a large military medical center in Bethesda, Maryland, the ARI with M. tuberculosis was found to range from 0.4 to 2.6 percent for most occupational categories. It was not significantly different for those in patient contact and non-patient contact positions (38). However, the rate was 15.6 percent for respiratory therapists.

Boudreau and others studied the occupational tuberculosis infection risk at Jackson Memorial Hospital in Miami, Florida (39). They compared infection rates for 248 initially tuberculin skin test negative employees who worked exclusively on hospital divisions from which the laboratory had received respiratory specimens positive for M. tuberculosis (exposed employees) with the rates for 355 employees who worked on divisions from which no such cultures had been received (unexposed employees). The cumulative risk among exposed employees was 14.5 percent; among unexposed employees it was 1.4 percent. The risk in exposed employees did not vary with job classification within the patient care division setting. Ward clerks had a risk similar to that of nurses. On the other hand, risk decreased coincident with the implementation of infection control measures from 6.2 percent (13/209) in 1989 to 0.6 percent (1/158) in 1992, at which time there was no difference between the risk in exposed and unexposed employees.

In Table C-10 the calculated annual risks of infection are listed for five hospitals in the studies described above. These five studies are the only ones among those described that this author feels are adequate to permit this calculation, and even then the resulting ARIs can be taken as only approximate. The 8- to 10-fold disparity between Barnes Hospital in St. Louis and the two New York City hospitals is obvious. The ARIs for Grady Hospital and the military medical center are intermediate between these extremes. These differences may reflect both the tuberculosis exposure risk due to larger number of tuberculosis admissions and also greater community risk. There are also substantial differences in risk related to occupation in those studies for which data are available.

The importance of job category for the risk in health care workers exposed to aerosols is made clear by the ARI of 17.1 percent/year in respiratory therapists at the military medical center. With respect to risk by occupation, it should be noted that there is a consensus among infectious disease experts that there is no risk from fomites or dust, although the latter may contain tubercle bacilli (even when ground, dust contains few respirable particles). Thus, any risk among laundry workers, for example, is generally not thought to be occupational.

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

TABLE C-10. ARI with M. tuberculosis for Various Populations of Hospital-Based Health Care Workers (HCWs) as Calculated Directly from Reported Several Selected Surveillance Studies with Sufficient Data to Permit This Calculation

Health Care Worker Group (reference)

Year

Calculated ARI of HCWs (%/year)

Barnes Hospital, St. Louis (40)

1989–1991

0.4

Cabrini Medical Center, New York (32)

1991

Wards admitting tuberculosis patients

5.1

Other wards

4.0

St. Clare’s Hospital, New York (30,31)

1993–1994

3.3

Laboratory

2.3

Physicians and nurses

3.0

Social service

2.2

Housekeeping

6.7

Finance

1.9

Grady Memorial Hospital, Atlanta (33)

1994

0.9

House officers (35)

1993–1997

1.1

Military medical center, Bethesda (38)

1994–1995

1.2

Respiratory therapy

17.1

Maintenance, engineering

2.6

Food service

2.6

Nursing technicians

2.3

Laboratory

2.1

Custodial

1.8

Practical nurses

1.8

Physicians

0.9

Registered nurses

0.4

NOTE: When applicable, all risks were calculated for periods following the implementation of current infection control measures.

Recent Risk for Health Care Workers in Locations of Low Tuberculosis Incidence

Since the United States is not homogeneous with respect to the incidence of tuberculosis, it is reasonable to expect that the risk to health care workers in areas of low incidence will be lower than the risks cited above in areas of higher incidence. Bailey and colleagues studied tuberculous infection among employees at Barnes Hospital, a 1,000-bed hospital in St. Louis, between January 1989 and July 1991 (40). At that time the new case rate in Missouri was 5/100,000/year and in St. Louis it was 11/100,000/ year. A total of 11.3 percent of employees were initially skin test positive. During the study period 0.93 percent of the initially tuberculin skin test negative employees converted to positivity, for an calculated annual risk of infection of 0.37 percent. The risk of infection was not correlated with occupational exposure; it was correlated with minority group status, resi-

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

dence in a postal code zone of low income status, and residence in a postal zone of high tuberculosis incidence. While the same group of investigators reported an 8.6 percent conversion rate among physicians at Barnes Hospital, the latter finding is difficult to evaluate because prior tuberculin nonreactive status was based solely on the physician’s report of a prior test at an unspecified time (41).

Among 2,500 to 3,800 employees tested annually between 1986 and 1994 at a pediatric hospital in Cincinnati, Ohio, the tuberculin skin test conversion rates ranged from 0.03 percent to 0.28 percent per year (42). There was no correlation with occupational exposure, and an apparent cluster of five infections occurred. In a survey of 17 Minnesota hospitals, the tuberculin reactor rate among employees was 0.3 percent in 1989–1991 (43).

Managan and coworkers compared tuberculin skin test conversion rates by questionnaire survey in two groups of hospitals: 38 hospitals admitting patients with Pneumocystis carinii pneumonia (PCP) in high-HlV-infection-incidence areas and 136 randomly selected hospitals without significant numbers of PCP patients that admitted more than six tuberculosis patients annually (44). During 1992, the tuberculosis infection rate among employees of the hospitals with PCP patients was 1.2 percent. If fell during the following 5 years to 0.43 percent, a change attributed to the institution of better infection control measures. The comparable tuberculosis infection rates in the non-PCP hospitals were 0.43 percent initially and 0.26 percent finally. In the hospitals with PCP patients with low tuberculosis case loads, the rate of conversion actually increased, although the numbers were small, and this suggested to the authors that the risk of tuberculosis infection was principally in the community rather than in the workplace.

Summary of Risk in Hospital-Based Health Care Workers

Although the limitations of the available data must be recognized, certain conclusions seem reasonable. First of all, there does appear to be a risk of tuberculous infection incurred by health care workers in the workplace that in some job circumstances may be greater than that incurred in the community. Aerosol-generating procedures are particularly hazardous to exposed employees. Second, the risk varies geographically, as it does in the general population. Next, it also varies with the ethnic and demographic compositions of the employees. Finally, the workplace risk has been decreasing in recent years. Quantitatively, the studies described above would suggest recent occupational tuberculous infection risks of about 0.5 to 1.0 percent/year for hospitals in low-tuberculosis-incidence areas and about 1.0 to 5.0 percent/year for hospitals in high-incidence areas, with these risks falling steadily and influenced by implementation of appropriate infection control measures.

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

Risk in Other Than Hospital-Based Health Care Workers

The rule proposed by OSHA would cover individuals providing services not only in hospitals but also in other situations including nursing homes, correctional facilities, immigration detainment facilities, law enforcement facilities, hospices, substance abuse treatment centers, homeless shelters, medical examiners’ offices, home heath care providers, emergency medical services personnel, research and clinical laboratories culturing tubercle bacilli and processing infectious specimens, ventilation system workers serving buildings housing tuberculous patients, social service workers, personnel service agencies providing workers to covered facilities, and attorneys visiting known or suspected infectious tuberculous patients (45). While it is logical to believe that contact of uninfected persons with infectious tuberculosis patients may occur in these situations, published data that support this hypothesis are lacking in many and sparse in others of these cases. Much of what has been reported is in the form of descriptions of outbreaks for which no denominator exists, so that the risk cannot be quantified.

Risk in Nursing Homes and Similar Chronic Care Facilities

In 1995, about 1.5 million Americans, 89 percent of them age 65 or older, about 5 percent of the elderly population, resided in nursing homes, and they contributed 7.7 percent of the tuberculosis cases nationally in individuals older than 64 years (46, 47, 48). The age-specific case rate for these persons is 1.8 times that for older persons not in nursing homes.

Stead reported an outbreak of tuberculosis in an Arkansas nursing home in 1978, with the index case being an elderly man thought to have bronchogenic carcinoma whose disease had not been adequately investigated (49). He was a gregarious individual who had many contacts throughout the home. Among 138 previously tuberculin-negative employees, 21 (15 percent) converted their skin tests and one developed active tuberculosis. In 1980 an outbreak of tuberculosis occurred in a Washington State nursing home after an elderly long-time resident was found to have sputum smear-positive tuberculosis (50). Upon investigation, 11 other cases of active tuberculosis were identified in the same facility. A skin testing survey found that 38 of 87 employees (44 percent) had newly positive tuberculin reactions. The air in this facility moved from patient rooms through dining and activity areas into two exhaust vents in the corridor. In both of these outbreaks, the diagnosis of the index case was not suspected for a substantial period of time.

In 1987 Price and Rutala published the results of a questionnaire survey of 12 long-term-care facilities in North Carolina; 101 skin test conversions occurred among 9,545 (1.1 percent) employees during the years

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

1981 through 1984 (51). The mean time interval was 5 years (calculated ARI = 0.21 percent/year). During the study period, annual conversion rates varied from 0.4 to 1.9 percent, with no apparent secular trend. Tuberculin conversion rates in the institutions’s patients were similar. There was wide variability in the skin testing techniques used, and these figures can be considered only approximate.

Risk in Correctional Facilities: Prisons and Jails

Studies in prisons and jails must be considered with the understanding that, among other variables, prisons typically house long-term inmates and jails detain many people for very short periods. The spread of multidrug-resistant tuberculosis among prisoners in New York City and State jails and prisons provoked great concern for the employees of those institutions. For example, in 1988 and 1989, one-quarter of the 205 tuberculosis cases in Nassau County, New York, were associated with a jail (52). Although inmates were screened on admission, there was no screening or infection control program for employees. Statewide, the incidence of active tuberculosis among New York prison inmates increased from 15/100,000/year in 1976 to 139/100,000/year in 1993 (53). Nationally, inmates of correctional facilities contribute just under 2 percent of the tuberculosis case load (48). The age-adjusted case rate for adult inmates is 3.9 times higher than that for the general population.

A system-wide annual tuberculin skin testing program for New York State prison employees was instituted in 1991–1992, and Steenland and coworkers reported on the conversions found at a 1-year follow-up (53). Overall, the conversion rate was 1.9 percent among 24,487 employees. Rates ranged from 1.4 percent in prisons with no known tuberculous inmates to 2.6 percent in prisons with more than the median number of tuberculous prisoners.

Transmission of tuberculous infection from inmates to correctional facility personnel has been documented in several published reports from California penal systems. Two of 11 prison infirmary employees converted their tuberculin skin test after contact with an infected prisoner in 1990–1991 (54). In two other outbreaks, employee tuberculin test conversions occurred in 9 of 319 (2.8 percent) and in 11 of 223 (4.9 percent) employees (55). In all cases, the conversions occurred within 2 years of a previously negative test. In a 1981 outbreak, one employee developed active tuberculosis (56). No information on employee skin test conversions was reported.

A 1994 outbreak of tuberculosis in a Texas prison housing a number of mentally retarded prisoners centered on a classroom used for education of these inmates (57). RFLP analysis demonstrated clustering of the patients. The report does not provide information allowing an assessment

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

of the infection risk to prison workers, but an instructor was among those who developed active tuberculosis.

Jones and colleagues studied the transmission of tuberculosis in a city jail in Memphis, Tennessee, where inmates were housed for a median of 1 day, often returning several times to the same facility, commonly housed in rooms holding up to 36 inmates (58). During a 3-year period beginning in January 1995, 38 inmates were recognized as tuberculous, and five guards developed tuberculosis. RFLP fingerprinting demonstrated that one strain of M. tuberculosis was responsible for the disease in 16 of 24 inmates for whom results were available and two of the five guards. Tuberculin testing of guards revealed a conversion rate of 2.7 percent in an unknown time period and of 1.2 percent during a subsequent 1-year interval.

Two studies of tuberculosis in prisons are of particular interest because they give some insights into the risk of tuberculous infection in relation to that in the community. In a study of 28 contact investigations in New York City correctional facilities, Johnsen noted that the tuberculin conversion rate among inmates exposed to sputum smear-positive prisoners with tuberculosis was 6.6 percent (59). On the other hand, when the investigation revealed that a putative index case did not, in fact, have tuberculosis, the conversion rate was 5.5 percent, not significantly different from the rate among those exposed to documented cases of tuberculosis. Johnsen suggested that some of the conversions were confounded by booster effects.

Erdil and Stahl reported preemployment tuberculin reactor rates for the Connecticut Department of Corrections for 1991 and 1992 (60). Because they reported age cohort-specific data, it is possible to calculate the actual annual risk of infection that these individuals brought with them to the workplace from the communities in which they resided. In this respect, this report is nearly unique and of considerable importance. For the 25- to 40-year-old age range, the calculated annual risk of infection was 0.18 percent/year. This rate is relatively high when compared to that for the adult U.S. population as a whole, but it is similar to the 0.20 percent/ year estimated ARI for black males.

Risk in Homeless Shelters

That tuberculosis is a problem among the urban homeless is well known, having been widely publicized in the lay press. In New York City, 68 percent of tuberculosis patients discharged from Harlem Hospital in 1988 were homeless (61), and 30 percent of all tuberculosis cases in 1991 were homeless (62). The shelters where these individuals spend their nights are often in substandard buildings with limited ventilation, and the sleeping conditions are generally crowded, thus facilitating the spread of airborne infections among the clients. Using both drug sensitivity pat-

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

terns and mycobacterial phage typing, Nardell and colleagues convincingly demonstrated transmission of tuberculosis among the clients of a homeless shelter in Boston in 1983 (63). An outbreak of tuberculosis in a poorly ventilated shelter for homeless men in Seattle, Washington, in 1987 was described by Nolan and coworkers (64). In San Francisco, a study conducted in 1993 and 1994 demonstrated by RFLP analysis that the M. tuberculosis isolates from 24 of 34 homeless tuberculosis patients belonged to six clusters, thus providing strong evidence for transmission of infection among these homeless individuals (65).

Despite the well-recognized risks of transmission of tuberculous infection in homeless shelters, there are almost no data concerning infection rates in the staff of these facilities. In fact, many of the workers at these shelters are drawn from the clients themselves, and they tend to be transient, often unavailable for repeated skin testing, and frequently tuberculin-positive. In the only published report giving information on infections among staff found in the author’s literature search, Curtis and colleagues from CDC studied an outbreak occurring in a homeless shelter for men in Syracuse, New York, in 1987 and 1988 (66). Seventy percent of the clients and staff of the shelter were tuberculin-positive. Tuberculin skin test conversions were documented in two of eight previously tuberculin-negative staff members. Perhaps reflective of much of the generally transient nature of shelter staffs, 52 additional staff members who may have been exposed were not available for skin testing.

Risk in Other Nonhospital Health Care Situations

Layton and coworkers studied a single-room-occupancy hotel used to shelter homeless persons with AIDS (67). Sixteen cases of tuberculosis were found among 116 persons surveyed; 8 of them were compliant with antituberculous therapy, 4 noncompliant, and 4 not under treatment. None of 11 employees had tuberculosis, and the authors found “[no] evidence of recent tuberculous infection” in them, although no skin test data were reported. These employees worked in a small lobby area that was reasonably well ventilated and not conducive to socializing with the residents (P.Kellner, personal communication).

Pierce, Sims, and Holman reported that 11 of 65 (17 percent) of workers in a residential hospice for AIDS patients converted their tuberculin skin tests after a patient with tuberculosis spent 29 days in the facility prior to being recognized as having tuberculosis (68). Information about the HIV infection status of the employees was not given, nor was information about ventilation in the facility. A tuberculin test conversion was documented in one employee of a residential substance abuse facility in Michigan where a client was found to have multidrug-resistant tuberculosis in 1989 (69).

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

Data relating to ambulatory facilities and their employees are sparse. An outbreak of tuberculous infection occurred among health care workers in a Palm Beach County, Florida, clinic in 1988 (70). Of 30 previously skin test-negative employees, 17 became tuberculin-positive. The clinic ventilation system provided greater than 90 percent recirculation of air with less than one-half fresh air changes per hour. In a nonoutbreak setting, 766 tuberculin-negative health care workers in 16 urban ambulatory care units caring for HIV-infected patients, six of which were located in greater New York City, participated in a prospective tuberculin skin testing study in 1992 and 1993 (71). The conversion rate in these individuals was 1.6 per 100 person-years.

Prezant and colleagues studied prospectively a cohort of New York City prehospital health care workers consisting of nearly 200 emergency medical technicians and paramedics who had been stably employed in their positions for at least 15 years (72). Documented tuberculin skin test conversions occurred in one worker in 1993, none in 1994, one in 1995, and three in 1996. Overall, the calculated annual risk of infection for this small group was 0.6 percent/year.

A single report described a survey of 56 American clinical microbiology laboratories processing samples for culture of mycobacteria (73). Fourteen tuberculin skin test conversions were noted, but neither the time interval nor the number of persons at risk were given, so that no conclusions can be drawn from this report.

Transmission of tuberculous infection from cadavers is well known, and autopsy rooms have been considered especially hazardous. Much of the past tuberculous infection risk for medical students cited previously was attributed to participation in autopsies. In a county medical examiner’s office in New York State 2 of 15 morgue assistants converted their tuberculin skin tests during a 15-month period (calculated ARI = 10.8 percent/ year) (74). This facility performed autopsies on deceased inmates from a nearby prison, and eight autopsies had been performed on tuberculous individuals during that time. In a further autopsy risk, prosector’s wart occurs as a result of direct percutaneous inoculation of M. tuberculosis; there are no data on its frequency.

Recently transmission of M. tuberculosis has been documented and much publicized in funeral homes. Gershon and coworkers surveyed 864 funeral home workers who were attending a convention of the National Funeral Directors Association (75). Of them, 101 (11.7 percent) were tuberculin skin test positive. Reactivity correlated positively with older age, male gender, and nonwhite race. After controlling for these factors, reactivity was twice as frequent among embalmers as other funeral home employees.

Sterling and colleagues reported the first episode of documented transmission of tuberculous infection from a cadaver to an embalmer (76).

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

In this case, the deceased individual had had AIDS and partially treated tuberculosis. A sputum culture was positive on the day of death. Close family members were exposed but not infected. The mortuary employee who embalmed the body subsequently developed tuberculosis, and the organism was shown by RFLP typing to be identical to that of the cadaver. Aerosolization from the airway during the embalming process was suggested as a possible means of transmission. One other case of well-documented transmission of M. tuberculosis during embalming, again with identical strains of tubercle bacilli as determined by RFLP typing, has recently been reported in abstract form (77).

Summary of Risk in Other Than Hospital Based Health Care Workers

The data are too few to permit any generalizations about the magnitude of the occupational tuberculosis risk for health care workers in nonhospital situations. There probably is a risk, and it probably varies with the incidence of tuberculosis in the populations served by the facilities. Although data in this regard are scarce, ventilation, recognition of cases of tuberculosis, and isolation procedures may be less adequate in nonhospital settings than in hospital settings. It is also possible that workers in these settings may have community-based infection risks that differ from those of hospital employees. Table C-11 summarizes the annual risks of infection calculated from three studies deemed adequate to support this calculation.

Risk Assessment by the Occupational Safety and Health Administration

OSHA has proposed a rule to enforce infection control measures on all facilities employing health care workers (45). As part of its proposal OSHA

TABLE C-11. ARI with M. tuberculosis for Three Populations of Nonhospital-Based Health Care Workers (HCWs) as Calculated Directly from Reported Surveillance Studies with Sufficient Data to Permit This Calculation

Health Care Setting (Reference)

Year

Calculated ARI of HCWs (%/year)

Nursing homes, North Carolina (51)

1980–1985

0.21

Prisons, New York State (53)

1991–1992

Exposed workers

2.6

Nonexposed workers

1.4

Prisons, New York City (59)

1990

Exposed workers

6.6

Nonexposed workers

5.5

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

conducted a risk assessment using some of the data cited above. For its estimation of the annual risk of infection in general populations, OSHA developed a model based on relating risk of infection to incidence of disease. Estimates of the prevalence of tuberculous infection in the United States were also provided to OSHA by Dr. Christopher Murray of Harvard University. OSHA concluded that the overall annual rate of infection in the general population of the United States varied by state, from a low of 0.0194 percent/year to 0.3542 percent/year, and chose a population size-weighted average of 0.146 percent/year for the country as a whole.

As its database for estimating the annual rate of tuberculous infection in health care workers, OSHA used information published and obtained directly from the state of Washington (29, 45), the state of North Carolina (45, 78), and Jackson Memorial Hospital in Miami, Florida (39, 45, 79). Using these data, OSHA estimated that the occupational risk in Washington was 1.5 times, that in North Carolina was 5 times, and that at Jackson Memorial Hospital 9 times that for the general population of the surrounding state, region, or community. Similar estimates were made for workers in nonhospital settings. For Washington State the occupational risk for employees of long-term-care facilities was judged to be 11 times that for the general population and for home health care workers it was 2 times that for the general population. OSHA’s risk estimate for the population of the United States as a whole in 1994 is about three times that of 0.05%/year considered by the author to be his best estimate of the national rate.

Risk Assessment in Relation to Job Category in Studies by the Centers for Disease Control and Prevention

The most careful attempts to assess the occupational tuberculosis risk of health care workers in relation to their workplaces and the communities in which they reside are studies conducted by the Division of Tuberculosis Elimination of CDC. These investigations include some of the only prospective studies of the problem. They are also notable because they all included initial two-step tuberculin skin testing to minimize confounding booster effects. Some of them have not yet been published, but abstracts were kindly made available to me by their authors, who gave me permission to cite them.

Panlilio and Burwen followed 1,961 initially tuberculin-negative health care workers in Boston and New York City at 6-month intervals beginning in April 1994 and reporting their results in abstract form in May 1996 (80). Overall, 30 (1.5 percent) conversions were documented. Conversion was correlated with foreign birth, Asian race, and recent entry into the United States. The authors concluded that it was difficult to determine the source of infections in their subjects.

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

In a national questionnaire survey of 1,494 hospitals Sinkowitz and coworkers found conversion rates based on reports from these hospitals of 0.6 to 0.7 percent/year for 1989 through 1992 (81). Bronchoscopy was associated with a high conversion rate of 3.7 percent/year among personnel. Respiratory therapists were also at high risk, with a rate of 1.0 percent/year. The main body of this report focused on compliance with CDC infection control guidelines, and demographic data on the employees were not included.

In 1995, McCray, Curtis, Onorato, and colleagues initiated a prospective study of health care workers in 32 facilities caring for patients with tuberculosis in six states, New York City, San Francisco, and San Diego (E.McCray and A.B.Curtis, personal communications of data presented at a December 1999 workshop). The sites included nine hospitals, seven health departments, five correctional institutions, two long-term-care facilities, and nine others. All were sites at which care for tuberculosis patients occurred, many in areas with relatively high tuberculosis case rates. During the next 3 years, a skin test conversion rate of 0.8 percent (112/ 13,597) was observed (calculated ARI = 0.28 percent/year). The rate was highest in New York City at 2.4 percent (calculated ARI = 0.81 percent/ year), but no conversions were observed among health care workers in Oregon, Colorado, and Florida. Conversions occurred with about equal frequency in correctional facilities (1.0 percent), health departments (0.9 percent), hospitals (0.8 percent), and long-term-care facilities (1.1 percent). Outreach workers had a risk approximately 2.5 times that of those in other occupations. Foreign birth and Asian or black race were independent predictors of risk, and after adjusting for these variables, no specific occupational risk remained. Some of the annual risks of infection that can be calculated from this study are shown in Table C-12.

TABLE C-12. Calculated Annual Risks of Infection Derived from Tuberculin Skin Test Conversion Data for Selected Groups of Health Care Workers (E.McCray and A.B.Curtis, personal communication)

Health Care Worker Group, Work Sites and Categories, Racial and Demographic Categories

Calculated Annual Risk of Tuberculous Infection (%/year)

Administrative/clerical

0.6

Nurses

0.5

Outreach worker

2.4

Doctor/physician’s assistant

0.6

Not Hispanic, white

0.3

Not Hispanic, Black

1.0

Asian

1.4

Hispanic

0.8

U.S.-born

0.4

Foreign-born

2.0

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

In reviewing their data, McCray and colleagues concluded that the risk of new tuberculous infection for most health care workers was not substantially greater in the workplace than in the community in which they resided. The annual risks calculated from the data of McCray and colleagues are higher than those estimated and previously presented in this report for general populations. Their data were based on prospectively collected and currently reported information available in more specific categories with better demographic stratification than the data used for the author’s estimations of ARIs. However, there may be a selection bias introduced by the choice of sites for the study of McCray and colleagues.

The CDC data suggest that the tuberculosis risks of health care workers closely parallel those for the communities in which they reside. This does not mean that transmission of tuberculosis infection does not occur in the health care-related workplace. It simply means that the occupational risk is not great compared with the community risk.

RISKS OF TUBERCULOUS DISEASE AND MORTALITY IN M. TUBERCULOSIS-INFECTED HEALTH CARE WORKERS

There are no studies available allowing one to estimate the risks of tuberculous disease and mortality in M. tuberculosis-infected health care workers per se. One must generalize from what is known about these risks in the general population. This risk has frequently been stated to be about 10 percent over the life of the infected individual, but the available data suggest that it is closer to 5 percent, with about half of the risk occurring in the first 1 to 3 years after infection. In fact, the risk of tuberculosis for infected health care workers should be less than that for other persons because they work in circumstances that are optimal for monitoring of tuberculin test conversion, for implementation of therapy of latent infection, and for education and orientation concerning the importance of this form of therapy. Isoniazid treatment of latent tuberculous infection has been shown to reduce the risk of disease by about 60 percent (82). Similarly, the mortality risk should be low because health care workers should have prompt access to detection and therapy of disease. In considering these risks, it is important to distinguish between those in immunocompetent persons and those in immunocompromised individuals.

Risk for Immunocompetent Health Care Workers

Longitudinal Surveillance of Tuberculin Skin Test Reactors Not Treated for Latent Infection

J.Arthur Myers and coworkers traced University of Minnesota medical students who were tuberculin-positive at medical school entry or who

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

converted their tuberculin reactions while students in the classes of 1930 to 1953 (83). Among 1,480 such students, 1,353 were alive at the time of follow-up in 1953; none of the decedents had tuberculosis at the time of death. In total, there were 39,205 person-years of follow-up. There were 92 cases of clinical tuberculosis in these individuals, or a rate of 6.2 percent (92/1,480). It is possible that this rate is low because of the short period of follow-up of recent reactors. Myers and colleagues used tuberculin skin testing techniques with high doses of old tuberculin. While Minnesota is a geographic region where nonspecific reactivity is rare, it is also possible, although not likely, that the number of reactors was overstated, again leading to underestimation of the risk.

In a parallel study covering the same time period, Myers and colleagues surveyed the graduates of three Minnesota nursing schools (84). Follow-up information was obtained on 2,880 of 3,192 graduates (90.2%). Of nursing students who either were tuberculin reactors on nursing school entry or who became tuberculin positive during their nursing studies, 5.2 percent (33/637) developed clinical tuberculosis. As with the earlier studies, the caveats about possible underestimation of the risk apply. In both the medical and nursing student populations, the risk was greater for students who converted in school than for those who were infected prior to entry. This observation is consonant with others that suggest that the primary school years may be years of infection with a relatively low risk of subsequent disease in comparison with the risk from infection during the years of young adulthood.

A longitudinal study of tuberculin reactors in Britain from 1933 to 1944 (Prophit study) has been recently reanalyzed by Sepkowitz (85). Nearly 1,500 medical students and more than 3,000 nurses were followed for a decade. Among medical students, the rates were 1.0/100 person-years for females and 0.6/100 person-years for males. Nurses were classified as high and low exposure depending on their current work status. In the high-exposure group, the tuberculosis incidence was 1.5/100 person-years, and in the low exposure group it was 0.7/100 person-years. The higher attack rate among high-exposure nurses was thought by Sepkowitz to indicate exogenous reinfection as a source of some of the disease. As in the studies of Myers and colleagues, old tuberculin was used for skin testing.

In her postal survey of physicians who graduated from California medical schools prior to 1975, Barrett-Connor found that 5.0 percent (100/ 1,988) of doctors who had been tuberculin-positive on medical school entry or who converted their tuberculin tests later developed tuberculosis (86).

Lydia B.Edwards and colleagues obtained follow-up information as of the end of 1969 for 823,199 (85 percent of those tested) naval recruits tuberculin tested with 5 tuberculin units of PPD between 1958 and 1967

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

(87). Tuberculosis developed in 0.4 percent (111/28,478) of individuals initially tuberculin positive with reactions of 10 millimeters or greater. Tuberculosis developed in 0.03 percent (272/794,721) of those with initial tuberculin reactions smaller than 10 millimeters. The morbidity for men 10 percent underweight was three times that for men 10 percent overweight.

Horwitz, Wilbek, and Erickson followed more than 626,000 persons aged 15 to 44 years in Denmark who were tuberculin tested in 1950–1952 for 12 years (88). Their results were age stratified and are shown in Table C-13. It is clear that the risk was greatest in the postpubertal years and decreased later in adulthood.

Studies of Control Subjects in BCG Vaccination Trials

Useful data can be obtained from follow-up of the tuberculin-positive individuals excluded from BCG vaccination trials. In general, this information is excellent because the tuberculin skin testing was usually done by skilled, specifically trained individuals, the studies were done prospectively, and great effort was put into data management. For the purposes of this review, many of them have the disadvantage of having been conducted in children with follow-up through the adolescent and postpubertal years. Studies done in high-tuberculosis-prevalence, developing countries have not been considered here, as they are unlikely to represent the risks to American health care workers.

Sol Roy Rosenthal and coworkers gave BCG vaccine to student nurses in Chicago during the 1940s and early 1950s (19). Among initially tuberculin-positive students followed for 12 years, tuberculosis developed in 0.7 percent (3/420).

The British Medical Research Council conducted a trial of BCG vaccination among more than 58,000 schoolchildren in 1950–1952 and reported results of a 15-year follow-up of 54,239 of them (89). Including as tuberculin positive both those who reacted to 3 tuberculin units of PPD and those

TABLE C-13. Tuberculosis Developing in Tuberculin Reactors by Age Group in Denmark (88)

Age at Initial Tuberculin Testing (years)

Number Tuberculin Positive

Number Developing Tuberculosis

Twelve-Year Incidence of Tuberculosis (%)

15–24

45,850

219

0.48

25–34

116,375

327

0.28

35–44

103,263

201

0.19

Total

162,225

546

0.34

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

who reacted only to 100 units, tuberculosis developed in 1.2 percent (406/ 33,518). Follow-up surveillance was conducted at 2.5-year intervals. The incidence in the first interval was nearly double that in ensuing follow-up periods.

Comstock reported 18-year follow-up data on a 1946 tuberculin survey and BCG vaccination program in Muscogee County, Georgia (90). Among 1,492 individuals positive for reactivity to 5 tuberculin units of PPD, 24 (1.6 percent) had developed tuberculosis. In a larger trial conducted in Muskogee County about 10 years later, Comstock and colleagues observed more than 22,000 individuals of all ages who reacted to PPD with more than 10 millimeters of induration for 20 years (91; G.W. Comstock, personal communication). Overall, 207 of the reactors (0.94 percent) developed tuberculosis. The average annual rate was 0.73 percent. Thirty-eight pecent of the cases developed during the first 5 years of observation.

Perhaps the most useful data on the occurrence of tuberculosis in tuberculin skin test reactors excluded from BCG vaccination trials comes from the report of Comstock, Livesay, and Woolpert that includes data from the Puerto Rican trial (92). Using case registers from both Puerto Rico and New York City, they traced more than 80,000 individuals with a mean follow-up of 18.9 years. They reported data by several demographic characteristics, which are presented in Table C-14. Not surprisingly, tuberculosis occurred much more frequently among urban than rural residents. It occurred more frequently in females than males and substantially more frequently in young children.

TABLE C-14. Tuberculosis Occurring in Nonvaccinated Puerto Ricans Identified in a BCG Trial, Initially Reacting to 1 or 10 Tuberculin Units of PPD with ≥6 millimeters of Induration (92)

Demographic Category

Number of PPD-Positive Persons

Number of Tuberculosis Cases

Percent

Total

82,269

1,400

1.7

Urban residence

47,021

844

1.8

Rural residence

35,248

56

0.2

White

67,184

1,152

1.7

Black

15,085

248

1.6

Male

43,100

674

1.6

Female

39,169

726

1.9

Age 1–6 years

3,906

119

3.0

Age 7–12 years

35,869

520

1.4

Age 13–18 years

42,494

761

1.8

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×
Studies of Control Subjects in Trials of Treatment of Latent Tuberculous Infection

The U.S. Public Health Service trials of isoniazid treatment of latent tuberculous infection provide useful 10-year follow-up information for the untreated, control groups (82). A variety of studies were conducted, of which those with household contacts and inmates of mental hospitals are probably the most relevant to health care workers. Overall, tuberculous infection marked by a PPD reaction of ≥10 millimeters occurred in 2.9 percent of infected household contacts and 1.2 percent of infected mental hospital inmates. Approximately one-third of cases developed during the first year of observation. Attack rates were higher in adults (essentially at the overall levels cited above) than children, and at least in the household contact group, the adult rate did not change through age 55.

A small study of a shipboard outbreak in the Dutch navy was cited by Ferrebee in her review (82). Tuberculosis developed in 12 of 128 seamen (9.4 percent) not given isoniazid in a trial of the effectiveness of this therapy, a figure much higher than that reported in any other investigation. This study, although small, is of interest because it reflects results in employed individuals. Shipboard exposures have been found to be more intense and have higher attack rates than those in other situations, and the population was probably skewed toward the young-adult age group that has the highest risk.

In an editorial dealing with the use of isoniazid for the treatment of latent tuberculous infections in young adults, George Comstock and Phyllis Edwards used published and unpublished data from both BCG trials and isoniazid chemotherapy trials to estimate the lifetime risk of tuberculosis among tuberculin skin test reactors (93). They noted that the risk declined with passing years. Lumping together their estimates of lifetime tuberculosis risks for tuberculin-positive black and white males and females, their estimates were approximately 3.5 to 4.5 percent at age 25, 3.1 to 3.6 percent at age 35, 2.6 to 3.0 percent at age 45, 2.0 to 2.5 percent at age 55, and 1.2 to 1.6 percent at age 65.

Impact of HIV Infection

HIV infection, even before the onset of frank AIDS, increases the risk of tuberculosis in infected individuals. In fact, tuberculosis is one of the major intercurrent infections of dually infected persons, and tuberculosis often occurs at a time when immune function is relatively well preserved.

Setting aside some excellent studies done in Africa as perhaps not applicable to American health care workers, the 2-year prospective study of Selwyn and colleagues conducted in a New York City methadone clinic in 1985–1987 provided what has been widely quoted and generally ac-

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

cepted as a measure of the risk of tuberculosis in dually infected persons (94). He found a tuberculosis risk of 7.9/100 person-years in PPD-positive, HIV-infected addicts and a risk of 0.3/100 person-years in PPD-negative, HIV-seropositive individuals. Isoniazid treatment of latent tuberculous infection was offered to all tuberculin-positive addicts, but the rate of compliance was low.

In a second study in 1987–1990, Selwyn and collaborators documented patient compliance with isoniazid treatment and also used a battery of delayed hypersensitivity antigens to assess skin test anergy (95). Among 25 persons who did not complete isoniazid, the tuberculosis incidence was 9.7/100 person-years. No cases occurred among those who completed treatment of latent infection. Among anergic individuals, the incidence was 6.6/100 person-years.

Useful information on the risk of tuberculosis in HIV-infected persons exposed to tuberculosis comes from two outbreak studies. Di Perri and coworkers described an outbreak of tuberculosis among AIDS patients in a hospital in Italy at which no patient with tuberculosis had been hospitalized during the previous 3 years (96). Ventilation included air recirculation. An individual with initially unsuspected tuberculosis was admitted, and an outbreak ensued. Among 18 exposed HIV-infected individuals, tuberculosis developed in eight, seven of them within 60 days.

Daley and colleagues described an outbreak in a congregate living facility for AIDS patients in San Francisco (97). A person with unrecognized tuberculosis was admitted to the facility; the diagnosis was made 6 weeks later after 3 weeks of progressive respiratory symptoms. Eleven of 30 exposed residents developed tuberculosis within the next 6 months, and organisms isolated from them were all of the same RFLP type as the organism from the index case. These two outbreaks demonstrate the enormous impact of HIV infection on susceptibility to tuberculosis.

In sum, one should probably accept a 10 percent annual risk of disease among tuberculin-positive persons who become HIV infected and a 35 to 45 percent early disease risk among AIDS patients who acquire infection with M. tuberculosis. Appropriate treatment of latent infection in both groups should reduce these risks.

Risk of Mortality Among American Health Care Workers with Tuberculosis

Clinical trials of antituberculosis therapeutic regimens conducted in the United States and elsewhere beginning the 1950s demonstrated low mortality rates among adequately treated individuals. The only modern American data come from United States Public Health Service trial number 21, a multicentered national trial of modern drug treatment regimens. Nine deaths occurred among 1,451 participants, 0.6 percent (98). HIV

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

status of the participants in this trial was not determined as part of the study and was generally unknown. One of the nine persons who died was known to be receiving treatment for AIDS at the time of death, however. Of the other eight, at least six were noncompliant or did not complete prescribed therapy because of drug toxicity. Moreover, the causes of death reported in this trial were taken from death certificates, which may not have reflected the true cause (L.Geiter, personal communication, December 2000).

A large portion of individuals dying of tuberculosis have the diagnosis made at the time of death and hence do not receive therapy. Rieder and his colleagues examined this aspect of tuberculosis mortality in the United States for the years 1985 through 1988, a time period preceding the major explosion of both AIDS and multidrug-resistant tuberculosis in America (99).

Overall, 5.1 percent of tuberculosis diagnosed nationwide in those years was recognized at the time of death. During those years, there were a total of 7,210 tuberculosis deaths in the United States (1). Rieder and coworkers identified 4,373 diagnoses made at death. This represents 60.7 percent of the total deaths due to tuberculosis for those years.

Tuberculosis is not evenly distributed among Americans (1). About 23 or 24 percent occurs in individuals over the age of 65; presumably most of them are no longer in the work force. Nearly 60 percent occurs among the unemployed. Six percent of patients are inmates of correctional facilities; 6 percent are homeless; and 3 percent are residents of long-term-care facilities. Reduced access to health care among the homeless and the unemployed can be presumed to increase their risk of being diagnosed and treated late or not at all and, in turn, their risk of death from untreated tuberculosis.

HIV infection and drug resistance increase the mortality risk. During the decade prior to the HIV epidemic, Goble and colleagues at a national referral hospital noted a rate of mortality of 20.1 percent (27/134) among patients with tuberculosis due to organisms resistant to both isoniazid and rifampin (100). Data from 466 patients with a culture positive for M. tuberculosis in New York City in April 1991 were assembled by Frieden and collaborators (62). Follow-up of these patients was achieved until death or for 14 months. The case fatality rate for patients with multidrug-resistant organisms who were HIV infected was 80 percent; for HIV-uninfected individuals it was 47 percent.

In summary, the risk for immunocompetent individuals in the United States of dying from appropriately treated tuberculosis due to drug-susceptible organisms is vanishingly small. For health care workers it should be smaller than for the general population because they should have the advantages of more rapid diagnosis and institution of appropriate therapy

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

and should not come from the malnourished, often homeless population that contributes substantially to national tuberculosis mortality.

Summary of Risks of Tuberculous Disease and Mortality Among M. tuberculosis-Infected Health Care Workers

In the surveillance studies cited above the methods of tuberculin skin testing, the completeness of follow-up, and the definitions of tuberculin positivity and of tuberculosis varied, and the rigor of examination for tuberculosis may also be open to challenge. Yet certain generalizations seem justified.

First, the attack rates among tuberculin reactors is substantially lower than the oft-stated 10 percent. Even if risks observed during the first few years after infection are projected forward in linear fashion, it is hard to envision a cumulative risk as high as 10 percent. The lifetime risk estimates by Comstock and Edwards (93) suggest that perhaps 3 percent should be chosen; other studies suggest a rate closer to 5 percent.

Next, although the risk cannot be converted to annual risk in any of them, it is apparent from these studies that the risk diminishes with the passage of time. In those studies in which age-specific data are presented, the risk among adults is greatest in the young adult, postpubertal years. This is the age when many individuals enter the health care workforce, but it is not representative of the many older health care workers.

The disease risk is dramatically increased in immunocompromised individuals. The risk of tuberculosis in infected persons is substantially reduced by appropriate treatment of latent infection, and health care workers should be ideally situated for the use of such treatment. Tuberculosis mortality risk in immunocompetent health care workers with tuberculosis not due to multidrug-resistant organisms is probably close to zero.

ACKNOWLEDGMENTS

This review could not have been accomplished without the help of others whom the author wishes to acknowledge. The reference librarians at the Health Sciences and Allen Memorial Libraries of Case Western Reserve University were helpful in finding many of the articles reviewed here, including obtaining a few by interlibrary loan. Marilyn Field, Elizabeth Epstein, and Cara Christie of the Institute of Medicine were helpful in supplying additional background material. Amy Curtis and Eugene McCray at CDC kindly gave me permission to cite some of their unpublished work. Finally, I am grateful to the members and staff of the Institute of Medicine Committee on Regulating Occupational Exposure to Tuberculosis for helpful reviews of successive drafts of this paper.

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

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Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
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Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
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54. Campbell R, Sneller V-P, Khoury N, Hinton B, DeSouza L, Smith S, Howard J, Ciofalo F, Welsh AL, Krycia W, Mycroft F, Hooper K, Goldman L, Royce S, Dorfman B, Morita S, Coulter S, Rutherford GW. Probable transmission of multidrug-resistant tuberculosis in a correctional facility—California. Morbidity and Mortality Weekly Report 1993; 42:48–51.

55. Prendergast T, Hwang B, Alexander R, Charron T, Lopez E, Culton J, Bick J, Shalaby M, Dewsnup D, Meyer H, Horowitz E, Khoury N, Mohle-Boetani J, Royce S, Chin D, Petrillo S, Miguelino V, Desmond E, Harrison R, Cone J, Greene C, Joseph M, Waterman S. Tuberculosis outbreaks in prison housing units for HIV-infected inmates— California, 1995–1996. Morbidity and Mortality Weekly Report 1999; 48:79–82.

56. Koo DT, Baron RC, Rutherford GW. Transmission of Mycobacterium tuberculosis in a California state prison, 1991. American Journal of Public Health 1997; 87:279–282.

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Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

60. Erdil M, Stahl K. Prevalence of tuberculosis skin test reactivity in preplacement applicants to the Connecticut Department of Corrections from 1991 to 1992. Journal of Occupational Medicine 1993; 35:1178–1179.

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Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

77. Lauzardo M, Duncan H, Hale Y, Lee P. Transmission of Mycobacterium tuberculosis to a funeral director during routine embalming (abstract). American Journal of Respiratory and Critical Care Medicine 2000; 161:A299.

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94. Selwyn PA, Hartel D, Lewis VA, Schoenbaum EE, Vermund SH, Klein RS, Walker AT, Friedland GH. A prospective study of the risk of tuberculosis among intravenous drug users with human immunodeficiency virus infection. New England Journal of Medicine 1989; 320:545–550.

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96. Di Perri G, Cruciani M, Danzi MC, Luzatti R, De Checchi G, Malena M, Pizzighella S, Mazzi R, Solbiati M, Concia E, Bassetti D. Nosocomial epidemic of active tuberculosis among HIV-infected patients. Lancet 1989; 2:1502–1504.

Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
×

97. Daley CL, Small PM, Schecter GF, Schoolnik GK, McAdam RA, Jacobs WR Jr, Hopewell PC. An outbreak of tuberculosis with accelerated progression among persons infected with the human immunodeficiency virus. New England Journal of Medicine 1992; 326: 231–235.

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Suggested Citation:"Appendix C The Occupational Tuberculosis Risk of Health Care Workers." Institute of Medicine. 2001. Tuberculosis in the Workplace. Washington, DC: The National Academies Press. doi: 10.17226/10045.
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Before effective treatments were introduced in the 1950s, tuberculosis was a leading cause of death and disability in the United States. Health care workers were at particular risk. Although the occupational risk of tuberculosis has been declining in recent years, this new book from the Institute of Medicine concludes that vigilance in tuberculosis control is still needed in workplaces and communities. Tuberculosis in the Workplace reviews evidence about the effectiveness of control measures—such as those recommended by the Centers for Disease Control and Prevention—intended to prevent transmission of tuberculosis in health care and other workplaces. It discusses whether proposed regulations from the Occupational Safety and Health Administration would likely increase or sustain compliance with effective control measures and would allow adequate flexibility to adapt measures to the degree of risk facing workers.

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