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.



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