Risk factors for a positive tuberculin skin test among employees of an urban, midwestern teaching hospital.

OBJECTIVE

To determine the prevalence and incidence of and the relative risks for positive tuberculin skin tests among employees of a large, urban teaching hospital.

DESIGN

Retrospective cohort study.

SETTING

Barnes Hospital, St. Louis, Missouri.

PARTICIPANTS

Hospital personnel employed at any time between January 1989 and July 1991.

RESULTS

684 of 6070 employees screened (11.3% [95% CI, 10.4% to 12.1%]) had positive tuberculin skin tests. Factors associated with a positive result were age (odds ratio, 2.02 per decade [CI, 1.87 to 2.18]; P < 0.0001); black race (odds ratio, 1.58 [Cl, 1.26 to 2.00]; P < 0.0001); Asian race (odds ratio, 16.7 [CI, 9.33 to 29.9]; P < 0.0001); Hispanic ethnicity (odds ratio, 9.45 [CI, 3.58 to 25.0]; P < 0.0001); and percentage of low-income persons within the employee's residential postal zone (odds ratio, 1.14 per 10% [CI, 1.05 to 1.23]; P = 0.001). Twenty-nine of 3106 employees who had at least two tests had skin-test conversions (0.93% [CI, 0.60% to 1.3%]); 15 of these conversions (52%) occurred among employees who had no direct contact with patients. Only the percentage of low-income persons within the employee's residential postal zone (odds ratio 1.39 [CI, 1.09 to 1.78]; P = 0.0075) was independently associated with conversion.

CONCLUSIONS

The most important associations with a positive tuberculin skin test were older age, minority group status, and the proportion of low-income persons within the employee's residential postal zone. Skin-test conversion was independently associated only with the percentage of low-income persons in the employee's postal zone. Stratifying employees according to degree of contact with patients or according to departmental group was not useful in determining risk for a positive tuberculin skin test or for skin-test conversion. For certain groups of employees, an exposure to tuberculosis in the community probably poses a greater risk than exposure in the hospital setting.