Bacille Calmette-Guerin (BCG) vaccine is one of the most commonly used vaccines in the world and is given to infants in the vast majority of low- and middle-income countries.

BCG is recommended in higher TB incidence areas because it has a documented protective effect against TB meningitis and disseminated TB in young children. It does not prevent primary infection and, more importantly, does not prevent reactivation of latent pulmonary infection, the principal source of bacillary spread in the community.

The impact of BCG vaccination on transmission of M. tuberculosis is therefore very limited (or there is no impact). BCG has not impacted the global epidemiology of TB. Because of variable efficacy, BCG is NOT recommended for use in the U.S.

BCG is not a contraindication to a TST but as noted there can be cross reactions between BCG and the TST. The primary advantage of IGRAs is that they do not cross react with BCG. Interpretation of a tuberculin skin test reaction is not changed for patients who have received BCG.

A reaction of > 10 mm (> 5mm in persons living with HIV) of induration should be considered infection with M. tuberculosis because:⌃

Since many BCG-vaccinated persons come from areas of high TB incidence, it is important that persons with a positive TST be evaluated for presence of TB disease and managed accordingly. Appropriate follow-up includes a careful medical history, CXR to rule out active TB disease, and evaluation for treatment of LTBI. An IGRA is the preferred LTBI test among individuals with a history of BCG vaccination but a TST is an acceptable test in BCG-svaccinated persons.