RISK OF INFECTION AND ESTIMATED INCIDENCE OF TUBERCULOSIS IN NORTHERNUGANDA

The main goals of our study were to evaluate: 1) the annual risk of tu berculosis infection (ARTI) and its annual decrease in Uganda; 2) the expected incidence of new tuberculosis cases and the notification rate ; and 3) the role of incentives given to children tested in increasing compliance with the survey procedures. The methodology is based on pe rforming the standard World Health Organization (WHO) tuberculin test on children of the same age groups at intervals of 10-15 yrs, identify ing infected persons by induration distribution analysis, and converti ng the prevalence rates detected into risk rates according to the ARTI model. Two thousand six hundred and twenty one school children aged 1 0 yrs old and bacilli Calmette-Guerin (BCG) nonvaccinated, in six stud y areas, were injected with two tuberculin units (TU) of purified prot ein derivative (PPD) RT 23 Copenhagen. The detected prevalence was 14/-1.4% (prevalence +/-95% confidence interval (95% CI)) and the ARTI v alue 1.2+/-0.9%, with an estimated annual decrease of 0.83% from 1958 to 1970 and 2.9% in the 1970-1987 period. The estimated expected incid ence of new cases in Uganda was 59 smear positive and 75 smear negativ e/extrapulmonary cases per 100,000 population in 1987, and 53 and 65, respectively, in 1990, with an overall 68% notification coverage. No s ignificant improvement in children returning for reading was observed in the group receiving incentives. We conclude that the average decrea se (2.9%) probably represents the natural decline of tuberculosis in U ganda. The coverage appears encouraging, although the ARTI detected co uld be underestimated, since the existing ARTI model was developed and validated before the human immunodeficiency virus (Hn? era. The impor tance of implementing adequate surveillance measures needs to be stres sed.