Epidemiology of tuberculosis in the United States

Abstract

Over the past 30 years, the risk of tuberculous infection is estimated to have declined by approximately 8.3 per cent annually. Over that period, the incidence of tuberculosis declined between 5 and 6 per cent annually, and the mortality rate has declined by about 7.3 per cent annually. However, tuberculosis has not receded uniformly among all segments of the population. The steepest decline has been observed in children five to 14 years of age, and the smallest decline has been observed in the elderly. Among adults, the decline has been steeper among whites than among other racial groups. In the 1980s, the annual risk of tuberculous infection in the general population is estimated to be as low as or lower than one in 10,000. It is narrowly concentrated among contacts, particularly close contacts, of known cases. The risk is highest among those who are exposed to sputum smearpositive cases. The incidence of tuberculosis in 1987 was 9.3 per 100,000 in the general population, but varied widely among different segments of the population. Although incidence increases with age among all race and ethnic groups, cases in minorities are concentrated among young adults, while cases in non-Hispanic whites are concentrated among the elderly. These differences are mostly attributable to differences in the risk of tuberculous infection, because, once a person is infected, the risk of progression to tuberculosis is similar among blacks and whites and among males and females (although two age groups, young children and adolescents, appear to be especially prone to progression). This suggests that with the passage of time, succession of new generations experiencing lower risk of infection will reduced the prevalence of tuberculous infection much more rapidly in the non-Hispanic white population than in minority populations. Among factors that modify the risk of progression from subclinical infection to tuberculosis are recency of infection and infection resulting from transmission by a sputum smear-positive source case. Only a few of the many risk factors that have been identified as promoting progression can be considered major contributors to morbidity, because most are not highly prevalent. A major exception may be HIV infection, which, although not yet highly prevalent in the US population, appears to be the strongest factor yet identified that is capable of promoting progression to tuberculosis.(ABSTRACT TRUNCATED AT 250 WORDS)