Occupational tuberculosis among deputy sheriffs in Connecticut: a risk model of transmission.

Objectives: The purpose of this study was to identify risk factors for tuberculin skin test conversions among non-infected deputy sheriffs in Connecticut and during an out-break in an urban lock-up.

Methods: 377 tuberculin skin-test negative sheriffs statewide in 1994-1995 and 37 sheriffs in the lock-up in 1995 were screened and questionnaires administered. Cellblock volumetric air flow was measured. The Wells-Riley model of airborne transmission [C = S(1-e-Iqpt/Q)] was applied to the epidemiologic and ventilation data.

Results: Statewide, of 377 sheriffs screened, 22 (5.8%) had positive skin tests. Risk factors included older age (p < .0075) and longer tenure (p < .036). In the lock-up, of 37 sheriffs screened, 4 (10.8%) had positive skin tests. Measured mean outside air flow per occupant (8.0 cfm; S.D. = 2.2) was below design (15 cfm) and recommended (20 cfm) standards. Mathematical modeling estimated that TB transmission would be reduced by 62.5 percent with ventilation at design specifications.

Conclusions: Inadequate ventilation may increase the risk for occupational transmission of tuberculosis. Since lock-ups do not have the time to conduct inmate TB screenings, supplemental engineering controls may be required.