12 weeks before TB diagnosis or onset of cough (whichever is longer)

Time during which a person with TB disease might have transmitted M. tuberculosis organisms to others. The infectious period typically is defined as 12 weeks before TB diagnosis or onset of cough (whichever is longer). If a patient has no TB symptoms, is AFB-smear negative, and has a non-cavitary chest radiograph, the presumed infectious period can be reduced to 4 weeks before the date of diagnosis of suspected TB. If the contact investigation indicates that TB transmission occurred throughout the identified infectious period, the time for contact investigation might need to be expanded beyond the basic 12 weeks

Period during which a person with TB disease might have transmitted M. tuberculosis organisms to others. For patients with positive AFB sputum smear results, the infectious period begins 3 months before the collection date of the first positive smear result or the symptom onset date (whichever is earlier) and ends when the patient is placed into AII or the date of collection for the first of consistently negative smear results. For patients with negative AFB sputum smear results, the infectious period extends from 1 month before the symptom onset date and ends when the patient is placed into AII (whichever was earlier)