Recent studies in the epidemiology of tuberculosis, based on the risk of being infected with tubercle bacilli

This review describes recent epidemiological studies, based upon the risk of infection with tubercle bacilli. In the Netherlands the risk of infection has been decreasing steeply and exponentially for many years, but in some developing countries there was little secular trend in the absence of intensive control measures. Variations in the risk of infection with age are being examined. A comprehensive statistical analysis has shown that the major risk of development of tuberculosis is following a recent primary infection; the risk is smaller following reinfection of a previously infected subject, and is very small indeed, in the absence of reinfection, if the primary infection took place more than 5 years previously.