Estimates of the incidence of pulmonary tuberculosis in developing countries are based on case reporting from local health laboratories or the annual risk of tuberculin skin test conversion. Because these methods are problematic, the authors used a multiple case ascertainment method to estimate the incidence of pulmonary tuberculosis from 1989 to 1993 in a Peruvian shantytown of 34,000 inhabitants. Two methods, face-to-face interview of all local inhabitants and examination of local laboratory smear records, were used for case gathering. The number of missed cases was estimated by capture-recapture analysis. Survey cases with positive smears were matched to age- and sex-matched controls and interviewed about socioeconomic conditions. The average annual incidence per 100,000 population was 364 (95% confidence interval 293-528) by capture-recapture methods. For the city encompassing the shantytown, the Peruvian Ministry of Heath reported an average annual incidence of 134 cases per 100,000 population. The authors conclude that, in Peru, alarming clusters of pulmonary tuberculosis are masked by government reports that pool zones of disparate incidence. Existing estimators of pulmonary tuberculosis incidence based on tuberculin conversion rates may be invalid in such areas. Within these hyperendemic areas, persons suitable for intensive prophylaxis efforts cannot be reliably identified by housing and socioeconomic risk factors.
PIP: A multiple case ascertainment method was used to estimate the incidence of pulmonary tuberculosis in 1989-93 in a shantytown with 34,000 residents near Lima, Peru. Face-to-face interviews with all residents yielded 191 reports of smear-positive tuberculosis diagnoses at shantytown laboratories and 97 diagnoses from out-of-town laboratories during the study period. Local laboratory smear records identified 354 positive smears, confirming the oral reports of 139 residents (73%) who reported diagnoses at local laboratories. The number of missed cases was estimated by capture-recapture analysis. An average annual incidence of 364 pulmonary tuberculosis cases per 100,000 population was calculated. In contrast, an average annual incidence of 134 cases/100,000 was reported by the Peruvian Ministry of Health for the city (South Lima) encompassing the shantytown. For hyperendemic areas such as shantytowns, various household and socioeconomic factors have been proposed as screening tools to identify those at risk of tuberculosis and in need of chemoprophylaxis. Survey cases with positive smears were matched with controls by age and sex and interviewed about socioeconomic conditions. Logistic regression analysis identified three socioeconomic factors that were protective against pulmonary tuberculosis: a longer residence in the shantytown (odds ratio (OR), 0.91/year; 95% confidence interval (CI), 0.82-0.99), a larger number of doors in the home (OR, 0.80/door; 95% CI, 0.70-0.93), and recent consumption of alcohol (OR, 0.61; 95% CI, 0.29-1.01). The positive predictive value of a model comprised of these three factors was below 1%, however. These findings indicate that clusters of tuberculosis cases in areas such as shantytowns may be masked by their proximity to areas of lower incidence in the absence of special case finding efforts.