sure to infectious tuberculosis.1 The occupational risk of tuberculosis is the probability of acquiring tuberculosis infection or active tuberculosis as a result of workplace exposure. Occupational risk is usually described statistically. Depending on the purpose of an analysis and the available data, it can be described in absolute terms (for example, as the risk of acquiring active tuberculosis during a year or a working lifetime for a particular category of worker) or in comparative terms (for example, one group’s risk compared with another’s). Comparative data help in identifying possible causes of or contributors to a problem (e.g., by comparing skin test conversion rates in different areas of a facility). Comparisons also help in understanding or communicating the magnitude of a problem and in assessing priorities for spending public health funds or other resources.

CDC lists two options for defining a case of active tuberculosis (CDC, 2000b). The laboratory definition requires either the isolation of M. tuberculosis from a clinical specimen or the demonstration of acid-fast bacilli in a clinical specimen when a specimen for culture was not or could not be obtained. The clinical case definition requires all of the following: a positive tuberculin skin test result; other signs and symptoms compatible with tuberculosis (e.g., abnormal and unstable radiologic findings or persistent cough), treatment with two or more antituberculous medications, and a completed diagnostic evaluation. Physicians may begin treatment of suspected infectious tuberculosis based on symptoms and risk factors while awaiting test results.

The definition of infection with M. tuberculosis is based only on test results, specifically, the results of the tuberculin skin test. The foundation of workplace surveillance programs has been the finding and investigating of tuberculin skin test conversions. As discussed in Chapter 2 and Appendix B, the tuberculin skin test has serious limitations as a community or workplace surveillance tool, particularly in communities and workplaces where tuberculosis is uncommon. In very low-prevalence locales, most skin test conversions will be false positives.

In general, occupationally acquired tuberculosis infection or disease is easier to define than to document. Nationally reported data on the occupational status of reported tuberculosis cases do not distinguish between cases originating in the workplace and those originating in the

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The committee was not charged with undertaking a formal risk assessment. A formal risk assessment involves four basic steps (NRC, 1983). Hazard identification relies on epidemiologic studies, animal studies, and other tools to determine whether exposure to an agent can increase the incidence of a health condition. A dose-response assessment attempts to determine the relationship between the dose of an agent and the incidence of an adverse effect. An exposure assessment seeks to estimate the intensity, frequency, schedule, duration, and route of human exposures and the size and kinds of populations exposed. Risk characterization involves estimation of the incidence of a health effect under the exposure conditions described by the exposure assessment.



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