Tuberculin Reactivity in School Age Children; Five-year Follow-up in Iran

Objective: Tuberculosis (TB) is an important infectious disease worldwide. Tuberculin skin test (TST) is the standard test for diagnosis of tuberculosis infection; Bacillus Calmette-Guerin (BCG) vaccination at birth has effects on this test. The aim of this study was to determine the prevalence of positive TST cases among 7- to 11-year-old primary school children and also to follow test-positive individuals for a five-year period. Methods: TST was performed on 10.184 children aged 7-11 years sampled by cluster random method in Kermanshah, West Iran. Those who had a positive test result (i.e. an induration of ≥15 mm following 72 hours of injecting 0.1 ml of 5 tuberculin units of purified protein derivative from Mycobacterium tuberculosis) were followed for five years to determine the presence of active TB. Also tuberculin positive rates at cut-off points of 10 mm and ≥15 mm for boys and girls and at different ages were derived and compared using the chi-squared test. Findings: Of 10.184 studied subjects, 830 (8.15%) cases showed positive TST. This rate was 8.7% in boys and 7.8% in girls (P=0.1). A significant linear trend was found between the tuberculin positive rates and age at all cut-off points (P<0.001). No active TB was detected during 5-year follow-up. Conclusion: The rate of positive TST cases in primary school children in Kermanshah, Iran was 8.15% with no new cases of active tuberculosis detection within five-year follow-up.