Must patients with suspected tuberculosis but negative smears be kept in isolation?

CDC Guideline

Kent A. Sepkowitz, Memorial Sloan-Kettering Cancer Center, New York, New York, USA.  Tuberculosis Control in the 21st Century.  Emerging Infectious Diseases 2001 Mar-Apr 7(2) 259-62

Summary:  The most common approach is the practice of considering discharge after 2 weeks of apparently effective therapy. Others wait until the sputum AFB smear converts from positive to negative, which may take 4 to 6 weeks. In areas where drug-resistant TB is common, a more cautious approach might be waiting for at least 2 weeks of smear-negativity or, if MDRTB is documented, for culture negativity.

Bryan CS, et. al.  Discontinuation of Respiratory Isolation for Possible Tuberculosis: Do Two Negative Sputum Smear Results Suffice?  Infection Control and Hospital Epidemiology 2006 May 27(5): 515-16.

Objective: To determine if traditional requirements for negative results from 3 sputum AFB smears before cessation of respiratory isolation is necessary.

Summary Result: Suggests proficiency of laboratory sputum testing is now sufficiently high to allow discontinuation of respiratory isolation if 2 sputum specimens test negative by AFB smear.  However, hospitals adopting this policy should monitor the proficiency of AFB studies on an ongoing basis.  Policy is not recommended for hospitals whose laboratories infrequently process specimens with positive AFB results.

Methods: Retrospective review of data from 25 consecutive patients with culture-proven tuberculosis that was diagnosed between Jan. 2000 and Dec. 2004.

Results: Performance of a third AFB smear did not detect tuberculosis in additional patients later proven to have pulmonary tuberculosis by means of culture.  Combined use of AFB smears and PCR detected tuberculosis in all but 3 patients by the time the second specimen had been analyzed.

Mathew P, et. al.  Are Three Sputum Acid-Fast Bacillus Smears Necessary for Discontinuing Tuberculosis Isolation?  Journal of Clinical Microbiology 2002 Sept 40(9): 3482-84

Objective: To evaluate the efficacy of three sputum AFB smears to rule out pulmonary tuberculosis.

Methods:  Reviewed mycobacteriology laboratory records from Sept. 1993 to Sept. 1998 for all sputum AFB smear and culture tests performed at two hospitals.

Results: Table 1 summarizes rates of positive test results for the three specimens.  No additional cases of pulmonary tuberculosis were identified in the third smear.


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