Change in the result of a test for M. tuberculosis infection that is interpreted to indicate a change from being uninfected to infected. With the tuberculin skin test, an increase of >10 mm in induration size during <2 years is defined as a conversion. A conversion is presumptive evidence of new M. tuberculosis infection and poses an increased risk for progression to TB disease. The term is applied to contacts only when previous skin test results are available. A change in tuberculin status during the window period is not necessarily consistent with this definition.

Culture considered to have converted to negative when two consecutive cultures, taken at least 30 days apart, are found to be negative. In such a case, the specimen collection date of the first negative culture is used as the date of conversion