[The factors related to the stagnation in the decline of tuberculosis incidence in Japan].

The mortality from tuberculosis in Japan had extremely decreased from the end of the 1940's to the beginning of the 1950's, due to the end of chaos after World War II and also due to the introduction of antituberculosis drugs. The rapid decline of mortality usually leads to the reduction in the infection risk of tuberculosis in the general population. Such a drastic change in the history of tuberculosis have been dividing general population into two groups, i.e. those who were born during the rapid spread of infection with tubercle bacilli and others who were born after. With the passage of time, the limiting age between those two groups reached 40-50 years old as of 1980. The elderly people who were infected with tubercle bacilli in the remote past, have a high risk of development of tuberculosis by endogenous breakdown. In addition, the population of the aged in Japan has been expanding very fast as compared to that in European countries. Owing to such a change of historical and demographical background, the proportion of the elderly cases developed to tuberculosis have increased considerably and it played a major role in a small decrease of tuberculosis incidence rates since 1980. On the other hand, a generation gap on the prevalence of tuberculosis infection caused the recent smallest reduction rate of incidence among young adults. As the majority of young people have not been infected with tubercle bacilli, since 1980, the micro-epidemic among adolescent and young adults have been reported often.(ABSTRACT TRUNCATED AT 250 WORDS)