Application of a mathematical model for calculating the best pattern for testing and treating a target population for pulmonary tuberculosis

Abstract

In order to calculate the best patterns for testing and treating a target population for pulmonary tuberculosis, a mathematical model was applied to the population aged 15 and over registered at the Public Health Center of Ribeirão Preto, SP, Brazil, during 12 consecutive months, from May 1973 through April 1974. Thirty thousand eight hundred and eighty-five persons living in this area were submitted to the tuberculin test, roentgenphotography, and bacteriologic examination of sputum (symtomatic persons only). The target populatoin was divided into five non-overlapping categories according to the results of the four tests: 1 - uninfected persons, 61.14%; 2 - infected persons, 37.84%; 3 - persons with lung shadows, 0.83%; 4 - only culture-positive patients, 0.07%; 5 - smear-positive patients, 0.12%. The average individual costs were also calculated along with cost evaluation for treatment at that Health Center - tuberculin test, Cr$ 0,30 (US$ 0.05); roentgenphotography, Cr$ 2,00 (US$ 0.30); smear examination, Cr$ 8,40 (US$ 1.30); sputum culture, Cr$ 22,00 (US$ 3.50); treatment, Cr$ 610,00 (US$ 96.82). The data obtained were used in the mathematical model desbribed by Revlle and Male, but were modified by the author for calculating the cost per active case treated in all possible logical combinations of the available tests. The best pattern set down by economic, epidemiologic, and clinical criteria was the following: tuberculin testing of anyone resorting to the Health Unit; after that, smear examination only for the tuberculin reactors, complemented by culture examination of negative sputum; treatment of all the bacteriologic positive patients. In those Health Units where conditions allow roentgenphotography, this resource ought to be included in the above sequence between the tuberculin test and smear examination.