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.

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