ABSTRACT
Rates of active tuberculosis disease are expressed as an annual incidence per 100,000 population. In the United States the rate was 87/100,000 in 1945 and had fallen to 6.4/ 100,000 by 1999. Thus, both active tuberculosis disease (i.e., culture-positive disease) and latent tuberculosis infection (i.e., positive tuberculin skin test result) are more common in Americans who were born when community rates of tuberculosis were higher. In 1945 approximately 50% of Americans had positive tuberculin skin test results. In the year 2000 this figure had fallen to <5%. However, because of waning cellular immunity with age, many persons who had positive tuberculin skin test findings in 1945 would have negative skin test results in 2000, exemplifying the high rate of false-negative tuberculin skin test findings in older populations. In developing countries the annual incidence of tuberculosis disease is often still in the range of 100-400/100,000, and rates of positive skin test results for persons from these regions are expected to be 50%–75%. The most common countries and regions of origin for foreign-born persons with tuberculosis in the United States are provided in Table 1.
