Preliminary study to antituberculosis chemotherapy in a region of sub-Saharian Africa: annual risk of tuberculosis infection calculation and tuberculin survey.

A tuberculin survey was performed in Arua District (577,799 inhabitants, recent return of refugees from Zaire and Sudan) in 1987 prior to the implementation of antituberculosis Chemotherapy and Control Programme. 50 clusters (schools) of 30 pupils each were selected in the 7 Counties by Sistematic Random Sampling. 1110 students 10 year old without BCG vaccination scar were injected with 5 IU of PPD; 1016 of them (more than 6% of the estimated district population of 10 year of age) came back after 72 hours for reading. 125 of them were positives (more than 10 mm of induration). The Infection Rate detected was 1.23% +/- 0.19. Considering the infection rates found by the Ugandan National Surveys done in 1950 (2.6%) and in 1970 (2.3%), and the slight slope of the curve calculated on those values we have underestimated the real Infection Rate in the district. To avoid this bias we suggest to include schools in sampling (it is simple and cost-effective) only if the Student's population is likely to be representative of the general population.