Tuberculin reactivity in a pediatric population with high BCG vaccination coverage

SETTING: The tuberculin skin test (TST) is often included in diagnostic alg orithms for tuberculosis (TB) in children. TST interpretation, however, may be complicated by prior Bacillus Calmette-Guerin (BCG) vaccination. We ass essed the prevalence of and risk factors for positive TST reactions in chil dren 3 to 60 months of age in Botswana, a country with high TB rates and BC G coverage of over 90%. METHODS: A multi-stage cluster survey was conducted in one rural and three urban districts. Data collected included demographic characteristics, nutri tional indices, vaccination status, and prior TB exposure. Mantoux TSTs wer e administered and induration measured at 48-72 hours. RESULTS: Of 821 children identified, 783 had TSTs placed and read. Of the 7 59 children with vaccination cards, 755 (99.5%) had received BCG vaccine. S eventy-nine per cent of children had 0 mm induration, 7% had greater than o r equal to 10 mm induration ('positive' TST), and 2% had greater than or eq ual to 15 mm. A positive TST was associated with reported contact with any person with active TB (odds ratio [OR] 1.9; 95% confidence interval [CI] 1. 02-3.6), or a mother (OR 5.1; 95% CI 2.1-12.4) or aunt (OR 5.3; 95% CI 2.0- 14.0) with active TB. TSTs greater than or equal to 5 mm (but not greater t han or equal to 10 mm) were associated with presence of a BCG scar. Positiv e reactions were not associated with age, time since BCG vaccination, clini cal signs or symptoms of TB, nutritional status, crowding, or recent measle s or polio immunization. CONCLUSION: The TST remains useful in identifying children with tuberculous infection in this setting of high TB prevalence and extensive BCG coverage .