Tuberculin skin test reactivity of health care students in a country with a low prevalence of tuberculosis.

SETTING

Health care students in Sweden.

OBJECTIVE

To analyse the distribution of tuberculin skin test (TST) reactions and epidemiological factors related to TST reactivity.

DESIGN

TST reactivity was analysed in 1190 students. A linear regression model was created for the relative contribution of background factors of TST reactivity. A subgroup of 287 non-vaccinated subjects was comparatively skin-tested with Mycobacterium avium sensitin and tuberculin.

RESULTS

Among non-bacille Calmette-Guérin (BCG) vaccinated students, 91% had no TST reaction (0 mm induration) and reactions of ≥ 10 mm were found in 2.9%, whereas 34% of BCG-vaccinated students had no TST reaction and 42% had reactions of ≥ 10 mm. The expected contribution to TST reactivity was 6.0 mm for a history of BCG vaccination, 3.0 mm for a country of birth with medium/high incidence of TB and 1.6 mm per 10 years of age. The sensitin reactions exceeded the TST reactions by ≥ 3 mm in 52% of the comparatively tested subjects with TST reactions of ≥ 1 mm.

CONCLUSION

BCG vaccination, cross-reactivity with non-tuberculous mycobacteria, geographic origin and age had a decisive influence on TST reactivity. Most non-vaccinated health care students were non-reactive, which highlights the need to organise preventive measures in settings where TB exposure is expected.