The delayed hypersensitivity response to Mycobacterium tuberculosis in infected persons may decline over time. Therefore, in previously infected individuals, an initial tuberculin skin test (TST) may show negative results but may "boost" the response to a second TST. This boosted positive reaction may be misinterpreted as a conversion reaction, implying recent infection. Two-step testing is therefore recommended for the initial tuberculin skin testing of adults such as health care workers who will be tested periodically. If the initial TST is negative, a repeat TST should be performed 1 to 3 weeks later. If the result is positive, the person should be considered infected and treated accordingly; if the result is negative, the person is not infected.1
- Repeat the test after 2 weeks to check for a booster reaction.
1. Core curriculum on tuberculosis. 4th ed. Centers for Disease Control and Prevention, Division of Tuberculosis Elimination; 2000. Available at http://www.cdc.gov.nchstp/tb/pubs/corecurr/default.htm.
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