The prevalence and predictors of tuberculin positivity in subjects screened for reasons other than contact investigation.

BACKGROUND

No previous studies have estimated the rates of tuberculin positivity (TP) in noncontact populations within the same community, which is important for prioritizing and implementing preventive measures.

OBJECTIVES

To estimate the prevalence and predictors of TP in noncontact populations.

METHODS

A retrospective analysis of tuberculin results of noncontact populations screened in British Columbia from 1990 to 2002 was conducted.

RESULTS

The period prevalence of TP in 59,791 screened subjects was 12.7% (95% CI 12.4% to 13.0%), 30.4% (95% CI 28.2% to 32.7%) and 60.9% (95% CI 60.3% to 61.6%) for Canadian-born non-Aboriginals (CBNAs), Canadian-born Aboriginals (CBAs) and foreign born (FB), respectively. After controlling for age and sex, independent predictors of TP included Bacille Calmette-Guérin (BCG) vaccination (OR 19.6, 95% CI 17.9 to 21.5), country of birth (CBA: OR 2.87, 95% CI 2.44 to 3.37; FB: OR 3.67, 95% CI 3.34 to 4.03) and the following populations: correctional centre residents (OR 4.14, 95% CI 1.87 to 9.15), residents of long-term care and community care facilities (OR 1.79, 95% CI 1.44 to 2.23), immigrants (OR 1.75, 95 % CI 1.50 to 2.04), health centre employees (OR 1.71, 95 % CI 1.56 to 1.88), volunteers (OR 1.38, 95% CI 1.14 to 1.68), self-referred healthy subjects (OR 1.30, 95% CI 1.15 to 1.48) and students (OR 1.27, 95% CI 1.19 to 1.35). CBAs, FB and male subjects were less likely to react to tuberculin than CBNAs and female subjects among those vaccinated with Bacille Calmette-Guérin (P<0.05).

CONCLUSIONS

Rates of TP correlate with disease rates by sex and origin. The continuation of tuberculin screening programs is warranted in noncontact populations with high TP rates, where unknown exposure to active cases is more likely to occur. Further research is needed to determine the reasons why a higher response to tuberculin occurs in BCG-vaccinated women and CBNAs.