The identification and treatment of latent tuberculosis infection can reduce the risk of a patient developing active tuberculosis and prevent infection of the public. Jasmer and colleagues review the diagnosis and treatment of latent tuberculosis. The decision to test should be based on the intention to treat the patient if the test is positive. Active tuberculosis should be ruled out in patients with a positive screening test by careful history, physical examination, and chest radiography. Candidates for testing include people likely to have been recently infected and people who are at high risk for active tuberculosis.

The criteria for interpreting the reaction to the tuberculin skin test as positive are outlined in the accompanying table. One criterion is an increase in induration of at least 10 mm within a two-year period. This change is known as “tuberculin conversion” and indicates a recent infection. Because the tuberculin skin test is not 100 percent sensitive, especially in immunocompromised persons, anergy testing has been used to confirm negative results. However, anergy testing is no longer recommended in patients who test positive for human immunodeficiency virus, and its use is not well defined in patients with normal immune systems.

Bacille Calmette-Guérin (BCG) is used outside the United States; however, because the majority of patients who have received the BCG vaccine are from countries with high incidence rates of tuberculosis, a history of BCG vaccination should not be considered when determining treatment.

Treatment options for latent tuberculosis include isoniazid, rifampin, or a combination of rifampin and pyrazinamide. Isoniazid is the first-line therapy and should be used for a minimum of six months, preferably nine months in adults and nine months in children. Directly observed treatment should be considered in patients when compliance is a concern. Concomitant pyridoxine should be administered in patients at risk for neuropathy, patients who are pregnant, and patients with seizure disorders. Age should not be considered a limiting factor because the decision to test and treat is based on the increased risk of developing active tuberculosis.