The use of an epidemiological model for estimating the effectiveness of tuberculosis control measures. Sensitivity of the effectiveness of tuberculosis control measures to the coverage of the population

Given an adequate definition of the disease problem in epidemiological terms, it is possible to measure the epidemiological effectiveness of control measures in terms of problem reduction. This is to be distinguished from the clinical efficacy of the same measures. The practical difficulty in assessing the epidemiological effectiveness of control measures experimentally can be overcome by the construction of simulation models and the use of computers, whereby the problem reduction associated with various control strategies can be estimated numerically.By varying the levels of certain parameters of the model systematically, the sensitivity of the effectiveness of control measures to the epidemiological, operational, clinical and social parameters of a situation can be assessed. A series of articles analysing this relationship is under preparation. This first article analyses the sensitivity of the effectiveness of BCG vaccination and of the chemotherapy of tuberculosis to changes in the coverage of the eligible population groups. A previously formulated postulate stating that the marginal effectiveness of these measures decreases as their coverage increases is validated by this first series of simulations. The significance of this finding for planning national tuberculosis control strategies is discussed, as well as possible bias in the method applied.