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U.S. Department of Health and Human Services


Core Curriculum on Tuberculosis, 2000

Chapter 8
Infection Control in Health Care Settings


Infectiousness is directly related to the number of tubercle bacilli expelled into the air. In general, persons who have or who are suspected of having pulmonary or laryngeal TB should be considered infectious if they are

  1. Coughing, are undergoing cough-inducing or aerosol-generating procedures, or have sputum smears containing acid-fast bacilli; and
  2. Not receiving therapy, have just started therapy, or have a poor clinical or bacteriologic response to therapy.

Patients who have drug-susceptible TB are no longer considered infectious if they meet all the following criteria:

  • They are on adequate therapy;
  • They have had a significant clinical response to therapy;
  • They have had three consecutive negative sputum smear results from sputum collected on different days.

Persons with extrapulmonary TB are usually not infectious. However, TB has been transmitted from a draining skin or tissue abscess containing M. tuberculosis. 1

Patients with TB disease should be closely monitored for response to therapy. Smear examinations should be done regularly (e.g., initially every 1 or 2 weeks). Persistent infectiousness is usually due to the patientís failure to take medications as prescribed or to drug resistance. These possibilities should be considered for any patient who does not clinically respond to therapy within 2 to 3 weeks.

In patients with drug-resistant TB, infectiousness may last several weeks or even months. In these patients, the response to treatment should be closely monitored, and for those in institutional settings, TB isolation should be maintained until infectiousness is ruled out. Continued isolation throughout hospitalization should be considered for patients with multidrug-resistant TB because these patients are more likely to experience treatment failure or relapse, which may prolong infectiousness.


Released October 2008
Centers for Disease Control and Prevention
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
Division of Tuberculosis Elimination -

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