Tuberculin reactivity among ninth-grade schoolchildren in the city of Havana, Cuba

Abstract

Objective: To determine the proportion of 14-year-old schoolchildren in the city of Havana, Cuba, with a positive tuberculin skin test, as an indicator of the prevalence of tuberculosis infection among them. Methods: Using single-stage cluster sampling, 1936 Mantoux (tuberculin) tests were carried out with ninth-grade students (cohort born in 1985) during the 1999-2000 school year in 20 basic high schools randomly selected in Havana. The tests were performed according to the standard technique recommended by the World Health Organization, and they were read after 72 h. The percentage of skin tests that were positive and the average diameter of the indurations were calculated for the cohort overall and for the two genders. The means and the percentages were compared using the chi-square test, with 95% confidence intervals. The computer software used was Epi Info version 6.0. Results: Of the tests read, 96% of them were negative (0-4 mm), 2.5% were doubtful (5-9 mm), and 1.5% were positive (>=10 mm). The percentage of reactivity was 0.1% when a cutoff value of 15 mm was used. The mean diameter of the indurations was 0.41 mm. No statistically significant difference was found between the genders. Conclusions: In this study, the proportion of schoolchildren with tuberculin reactivity, using an induration-diameter cut-off point of 10 mm, was very low (1.5%), and it was much lower (0.1%) when a cut-off point of 15 mm was used. The skin reactions with an induration diameter of >=10 mm could be the expression of a natural infection if one takes into account the low frequency of bacillary tuberculosis in Cuba and that there is an inverse relationship between the time elapsed from the BCG vaccination and the intensity of the response to tuberculin. Therefore, that would mean that in this case the point prevalence of tuberculosis infection in this group of schoolchildren would be 1.5%.