lung cavities, which imply prolonged illness and infectiousness). Table 2. Guidelines for estimating the beginning of the period of infectiousness of persons with TB, by index case characteristic Characteristic TB symptoms Acid-fast bacilli sputum smear pos Cavitary chest radiograph Recommended minimum beginning of likely period of infectiousness Yes No No 3 months before symptom onset or first positive finding (e.g., abnormal chest radiograph) consistent with TB disease, whichever is longer Yes Yes Yes 3 months before symptom onset or first positive finding consistent with TB disease, whichever is longer No No No 4 weeks before date of suspected diagnosis No Yes Yes 3 months before first positive finding consistent with TB Source: California Department of Health Services Tuberculosis Control Branch; California Tuberculosis Controllers Association. Contact investigation guidelines. Berkeley, CA. California Department of Health Services, 1998. Latent M. tuberculosis infection (or latent tuberculosis infection [LTBI]): See Infection Mantoux method: A skin test performed by intradermally injecting 0.1 mL of PPD tuberculin solution into the volar or dorsal surface of the forearm. This is the recommended method for tuberculin skin testing. Multidrug-resistant TB (MDR TB): TB disease caused by an M. tuberculosis strain that is resistant to at least INH and rifampin. Treatment regimens for curing MDR TB are long, expensive, and difficult to tolerate. The cure rate depends on the susceptibility of M. tuberculosis to alternative chemotherapy. Mycobacterium tuberculosis (M. tuberculosis ): The namesake member organism of M. tuberculosis complex, and the most common causative infectious agent of TB disease in humans. At times, the species name refers to the entire M. tuberculosis complex, which includes M. bovis and five other related species. NTCA: National Tuberculosis Controllers Association. Purified protein derivative (PPD) tuberculin: A material used in diagnostic tests for M. tuberculosis infection. In the United States, PPD solution (5 tuberculin units per 0.1 mL) is approved for administration as an intradermal injection as a diagnostic aid for M. tuberculosis infection (latent infection or TB disease). QuantiFERON®-TB Gold: An in vitro cytokine assay that detects cell-mediated immune response to M. tuberculosis in heparinized whole blood from venipuncture. QuantiFERON®-TB Gold (QFT-G) appears capable of distinguishing between the sensitization caused by M. tuberculosis infection and that caused by BCG vaccination. CDC recommends that QFT-G can be used in all circumstances in which the TST is 1 4
currently used, including contact investigations. QFT-G can be used in place of and not in addition to the TST. A positive QFT-G result should prompt the same evaluation and management as a positive TST. No reason typically exists to follow a positive QFT-G with a TST. For persons with recent contact to infectious TB, negative QFT-G results typically should be confirmed with a repeat test performed 8-10 weeks after the end of exposure.
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