Latent TB: The case for vigilance
To reduce morbidity and mortality from tuberculosis (TB), major health organizations recommend screening for latent TB infection in those who are at high risk. Here’s who requires your attention.
There are 2 screening tests for LTBI: TB blood tests (interferon-gamma release assays [IGRAs]) and the Mantoux tuberculin skin test (TST). Two TB blood tests are available in the United States: QuantiFERON-TB Gold Plus (QFT-Plus) and T-SPOT.TB test (T-Spot).
There are advantages and disadvantages to both types of tests. A TST requires accurate administration and interpretation and 2 clinic visits, 48 to 72 hours apart. The cutoff on a positive test (5, 10, or 15 mm) depends on the patient’s age and risk.4 An IGRA should be processed within 8 to 32 hours and is more expensive. However, a major advantage is that it is more specific, because it is unaffected by previous vaccination with bacille Calmette-Guérin or by most nontuberculous mycobacteria infections.
To rule out active TB ... If a TB screening test is positive, the recommended work-up is to ask about TB symptoms and perform a chest x-ray to rule out active pulmonary TB. Sputum collection for acid-fast smear and culture should be ordered for anyone with a suspicious chest x-ray, respiratory symptoms consistent with TB, or HIV infection.
Treatment for LTBI markedly reduces the risk for active TB. There are 4 options:
- Isoniazid (INH) plus rifapentine (RPT) once per week for 3 months.
- Rifampin (RIF) daily for 4 months.
- INH plus RIF daily for 3 months.
- INH daily for 6 or 9 months.
Details about the variables to consider in choosing a regimen are described on the CDC website.4,5
Know your resources. Local and state public health departments should have TB control programs and are sources of information on TB diagnosis and treatment; they also can assist with follow-up of TB contacts.6 Although LTBI is a reportable condition only in young children, any suspicion of community spread of active TB should be reported to the public health department.
