Which statement most accurately describes the relationship between a positive TST result and contagiousness?

Which statement most accurately describes the relationship between a positive TST result and contagiousness?

• A. Positive TST confirms contagiousness
• B. Positive TST indicates infection; contagiousness depends on whether TB is active
• C. Positive TST indicates no infection
• D. Positive TST indicates immediate contagiousness in all cases

Answer: (B)

A positive tuberculin skin test shows TB infection or prior exposure, not contagiousness. The test measures whether the immune system has been sensitized to Mycobacterium tuberculosis, but it cannot tell if the bacteria are currently active or being shed. Contagiousness depends on active TB disease, especially pulmonary or laryngeal TB with bacteria present in the sputum. Many people with a positive TST have latent TB infection and are not contagious. If TB is active, particularly with pulmonary involvement, contagiousness can occur; if TB is latent, there is no contagiousness.

A positive tuberculin skin test shows TB infection or prior exposure, not contagiousness. The test measures whether the immune system has been sensitized to Mycobacterium tuberculosis, but it cannot tell if the bacteria are currently active or being shed. Contagiousness depends on active TB disease, especially pulmonary or laryngeal TB with bacteria present in the sputum. Many people with a positive TST have latent TB infection and are not contagious. If TB is active, particularly with pulmonary involvement, contagiousness can occur; if TB is latent, there is no contagiousness.