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Early Recognition and Treatment of Latent TB

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 on page 1596. 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.

Criteria for a Positive Tuberculin Skin Test Size of reaction Persons in whom reaction is considered positive >=5 mm Persons with HIV   Close contacts of persons with infectious tuberculosis   Persons with an abnormal chest radiograph consistent with previous tuberculosis*   Immunosuppressed patients receiving the equivalent of >=15 mg of prednisone per day for >= one month >=10 mm Foreign-born persons recently arrived (less than five years earlier) from a country with high prevalence of tuberculosis   Persons with a medical condition that increases the risk of tuberculosis†   Injection-drug users   Members of medically underserved, low-income populations (e.g., homeless persons)   Residents and staff members of long-term care facilities (e.g., nursing homes, correctional institutions, homeless shelters)   Health care workers   Children younger than four years   Persons with conversion on a tuberculin skin test (increase in induration of >=10 mm within a two-year period) >=15 mm All others‡ HIV = human immunodeficiency virus. *--An abnormal chest radiograph consistent with previous tuberculosis reveals fibrotic opacities occupying more than 2 cm2 of the upper lobe; radiographs showing pleural thickening or isolated calcified granulomas are not considered to be suggestive of previous tuberculosis. †--Medical conditions that increase the risk of development of tuberculosis in the presence of latent tuberculosis infection include silicosis, end-stage renal disease, malnutrition, diabetes mellitus, carcinoma of the head and neck or lung, immunosuppressive therapy, lymphoma, leukemia, loss of more than 10 percent of ideal body weight, gastrectomy, and jejunoileal bypass. ‡--These persons should not be screened in the absence of an indication. Adapted with permission from Jasmer RM, Nahid P, Hopewell PC. Latent tuberculosis infection. N Engl J Med 2002;347:1862.

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.

CHUCK CARTER, M.D.
Medical editing fellow
Georgetown University Medical Center
Washington, D.C.

Jasmer RM, et al. Latent tuberculosis infection. N Engl J Med December 5, 2002;347:1860-6.

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