Several medical conditions can limit a successful immune response to tuberculosis infection and increase the likelihood of disease progression. Such conditions include human immunodeficiency virus (HIV) infection and AIDS, diabetes mellitus, silicosis, chronic renal failure, some cancers, advanced age, weight significantly less than recommended levels, and treatment with drugs that suppress immune system functioning. The risk of progression from untreated tuberculosis infection to active tuberculosis is particularly high in people with HIV infection or AIDS—approximately 10 percent per year. The Centers for Disease Control and Prevention (CDC) has recommended that health care workers with HIV infection be offered voluntary reassignments that minimize contact with patients with suspected or confirmed active tuberculosis (CDC, 1994b).
About 80 percent of cases of active tuberculosis involve the lungs (pulmonary tuberculosis), either exclusively or in combination with other sites (CDC, 1999b). The other most common sites of active tuberculosis are the lymph nodes, brain, bones, and kidneys.
Those with extrapulmonary tuberculosis and no coexisting pulmonary or laryngeal disease rarely infect others because the bacteria lack an easy route (i.e., the respiratory tract) to airborne transmission. Children and people with HIV infection are more likely than others to develop extrapulmonary forms of tuberculosis.
Without treatment, fatality rates for those with active tuberculosis may exceed 50 percent (Haas and Des Prez, 1995). With treatment, death rates drop to near zero for people who have well-functioning immune systems and drug-sensitive disease and who receive timely, appropriate care (Cohn et al., 1990; Combs et al., 1990). Among patients infected with multidrug-resistant strains of tuberculosis (especially patients with poorly functioning immune systems), death rates even with treatment may be as high as 90 percent (CDC, 1994b; Garrett et al., 1999).
The tuberculin skin test is the only currently available diagnostic tool for the detection of latent infection with M. tuberculosis.8 Although gen
In areas where tuberculosis is uncommon, screening of the general population by the tuberculin skin test is not recommended (ATS/CDC, 2000b). Targeted testing is recommended for people who are thought to be at higher risk of developing disease and who would benefit from treatment of latent infection. High-risk groups include people with HIV infection and certain other medical conditions, recent immigrants from countries where tuberculosis is common, and those with recent exposure to someone with infectious tuberculosis. Treatment for latent tuberculosis infection should be available to those who have positive tuberculin skin test results.