Infection with M. tuberculosis In contrast to active tuberculosis, no routinely collected, national data document the prevalence or incidence of infection with M. tuberculosis in the U.S. population overall or in major population subgroups. The last effort to collect systematic information on the prevalence of tuberculosis infection nationwide dates back to the 1971– 1972 National Health Survey. For that survey, trained personnel administered and read tuberculin skin tests for a national sample of American adults. Based on the results, analysts estimated the prevalence of skin test reactivity among adults aged 25 to 74 years to be 21.5 percent during the survey period (Engel and Roberts, 1977).
In the risk assessment section of its 1997 proposed rule on tuberculosis, OSHA presented an estimate of the prevalence of latent tuberculosis infection in the United States developed by Christopher Murray. Using a mathematical model of tuberculosis transmission, Murray estimated the prevalence of latent tuberculosis infection in 1994 to be about 6.5 percent for Americans over age 18 (62 FR 201 at 54199 [Table V-6] October 17, 1997).
Working from Murray’s prevalence estimates, OSHA estimated the weighted annual risk of infection for the U.S. population to be approximately 0.146 percent. For individual states, the estimates ranged from 0.02 percent in New Hampshire to 0.30 percent in New York and 0.35 percent in Hawaii. OSHA used these prevalence and incidence estimates as the bases for comparing the occupational risk of tuberculosis with the background risk of the disease in the general population (see Chapter 7).
In Appendix C, Daniel uses a technique for estimating the annual risk of tuberculosis infection based on the empiric ratio between this risk and the incidence of active disease (Daniel and Debanne, 1997). Using data derived from white male naval recruits between 1958 and 1965, he estimated this ratio to be approximately 150. When that ratio is applied to the 1998 tuberculosis case rate for the United States, it yields an annual risk of infection of approximately 0.05 percent per year, which is about one-third of the 0.146 percent per year figure used by OSHA in its risk assessment. The higher OSHA figure may reflect differences in the reference year used, their inclusion of racial and ethnic minorities, and possibly other factors such as the impact of HIV infection and AIDS since 1980.
Active Tuberculosis and Mortality from Tuberculosis Since 1994 (for the year 1993), the CDC has reported occupational information for people diagnosed with active tuberculosis. The CDC data do not allow one to draw conclusions about the source—workplace versus community—of workers’ exposure to tuberculosis.