Update on latent tuberculosis infection.

Latent tuberculosis infection refers to an asymptomatic, nontransmissible infection with Mycobacterium tuberculosis, carrying a 5% to 10% lifetime risk of progressing to active disease. One-half of this risk occurs within the first two years after infection. High-risk groups include recent immigrants from high-incidence countries, health care professionals, persons living or working in institutional settings, and homeless persons. Risk factors for progression to active disease include immunodeficiency, recent exposure to tuberculosis, and chronic kidney disease requiring dialysis. Tuberculin skin testing has several limitations, including the need for multiple office visits and the potential for false-positive results in patients who have received the bacillus Calmette-Guérin vaccine or been exposed to environmental mycobacteria. Interferon-gamma release assays address these deficiencies but are limited by their cost and requirement for blood processing. Interferon-gamma release assays are preferred in immigrants exposed to bacillus Calmette-Guérin and in patients who are not likely to return for interpretation of skin test results. Tuberculin skin testing is preferred for children younger than five years. Active disease should be excluded before initiating treatment. The newest treatment option of 12 weekly doses of isoniazid and rifapentine has similar or better effectiveness than standard nine-month therapy with daily isoniazid. A four-month regimen of daily rifampin is another alternative.