All people, except infants <6 months of age, should have a tuberculin skin test (TST; Mantoux) before BCG vaccination. Only immunocompetent people who have induration of <5 mm after a TST should receive BCG vaccine.
The TST uses a tuberculin purified protein derivative. This causes a hypersensitivity reaction in people who have a Mycobacterium tuberculosisinfection. Hypersensitivity reactions can also occur in:
The measles virus inhibits the response to tuberculin. Tuberculin-positive people may become tuberculin-negative for 4–6 weeks after measles infection, and measles-containing vaccines have a similar effect. 6,7
Because of this, the TST may be unreliable for at least 4–6 weeks in people who have received a measles-containing vaccine.
Interferon-gamma release assays (IGRAs) are a type of blood test that can detect M. tuberculosisinfection, but the TST is still the preferred method of screening for tuberculosis, unless the person has previously received BCG vaccine.8