Case-control study of the efficacy of BCG immunization against pulmonary tuberculosis in young adults in Santiago, Chile

Abstract

We performed a case-control study of the efficacy of BCG immunization against pulmonary tuberculosis in 15- to 35-year-old Chilean patients born during a period when BCG coverage was incomplete. Our aims were to determine BCG efficacy against pulmonary tuberculosis in young adults, to determine if repeated BCG immunization increased its protective effect, and to determine factors that could explain the failure of BCG immunization in patients with tuberculosis. We studied 68 patients who had pulmonary tuberculosis based on positive AFB in at least 1 of 2 sputum smears, a positive confirmatory culture and compatible chest roentgenogram abnormalities. The control group were 188 individuals without pulmonary tuberculosis seeking medical care for other ailments. The percentage of non-immunized individuals was 13.2 among patients with tuberculosis and 12.2 among controls. The vaccine efficacy calculated from these data was 10%. There was no difference in the percentage of individuals with 1, 2 and 3 BCG scars between tuberculosis patients and controls. The number and percent of individuals exposed to tuberculosis among BCG-immunized and non-immunized tuberculosis patients and controls were similar. No significant differences between BCG-immunized and non-immunized individuals were detected in tuberculosis patients or in the control group. However, tuberculosis patients as a group had significantly lower weight, education level, employment rate and family income than controls. These observations suggest that the development of pulmonary tuberculosis in BCG-immunized young adults is favored by the presence of genetic and/or acquired predisposing factors capable of overriding protective immunity induced by BCG vaccination.