METHODOLOGICAL ISSUES IN THE ESTIMATION OF THE TUBERCULOSIS PROBLEM FROM TUBERCULIN SURVEYS

Setting: National tuberculin skin test surveys. Objectives: To review the operating characteristics of the tuberculin skin test, to ascertai n the validity of estimating prevalence and risk of infection from tub erculin skin test surveys under various conditions, and to review cons taints in the estimation of the magnitude of the tuberculosis problem in the community from such surveys. Methods: This report utilizes hypo thetical and selected real data obtained in regional and national surv eys at various points in time to exemplify methodological issues. Resu lts: Risk of infection, the essence to be abstracted from tuberculin s kin test surveys, theoretically allows for a comparison of the extent of transmission of tubercle bacilli in various populations. However, t he conduct of tuberculin skin test surveys and the analysis and interp retation of their results are not free from important technical proble ms. Accurate estimation of infection prevalence is particularly vulner able to the great variability of the test's specificity under various circumstances. Furthermore, the annual risk of infection has averaging characteristics that preclude a rapid assessment of changes in transm ission patterns. Finally, estimates of infection risk do not necessari ly provide a standardized parameter to derive incidence of infectious cases, because of variations in the quality of intervention and varyin g risks of progression from latent infection to overt tuberculosis. Co nclusions: While tuberculin skin test surveys provide the currently mo st widely used means of assessing tuberculosis transmission patterns o ver prolonged periods of time in a community, results from such survey s must be interpreted with caution when accurate estimates of the tube rculosis problem are sought.