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Original Research: TUBERCULOSIS |

Molecular Evidence of False-Positive Cultures for Mycobacterium tuberculosis in a Taiwanese Hospital With a High Incidence of TB

Chih-Cheng Lai, MD; Che-Kim Tan, MD; Sheng Hsiang Lin, MD; Chun-Hsing Liao, MD; Chien-Hong Chou, MD; Yu-Tsung Huang, MD; Po-Ren Hsueh, MD
Author and Funding Information

From the Department of Internal Medicine (Dr Lai), Cardinal Tien Hospital, Taipei County; the Department of Intensive Care Medicine (Dr Tan), Chi-Mei Medical Center, Tainan; the Department of Internal Medicine (Dr Lin), Taipei County Hospital, Taipei County; the Department of Internal Medicine (Dr Liao), Far Eastern Memorial Hospital, Taipei; the Department of Internal Medicine (Dr Chou), National Taiwan University Hospital Yun-Lin Branch, Yun-Lin; and the Departments of Laboratory Medicine and Internal Medicine (Drs Huang and Hsueh), National Taiwan University Hospital, National Taiwan University College of Medicine, Taipei, Taiwan.

Correspondence to: Po-Ren Hsueh, MD, Departments of Laboratory Medicine and Internal Medicine, National Taiwan University Hospital, No 7 Chun-Shan South Rd, Taipei 100, Taiwan; e-mail: hsporen@ntu.edu.tw


Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestpubs.org/site/misc/reprints.xhtml).


© 2010 American College of Chest Physicians


Chest. 2010;137(5):1065-1070. doi:10.1378/chest.09-1878
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Background:  Isolation of Mycobacterium tuberculosis (MTB) from the clinical specimens of patients with suspected TB remains the gold standard for diagnosis of TB. However, false-positive MTB cultures can occur as a result of laboratory contamination.

Methods:  After reviewing the medical records of 400 TB cases identified during January 2008 to January 2009 by the infection control unit of a university-affiliated hospital in Taipei, Taiwan, five patients were considered as clinically suspected false-positive cases and were referred to a mycobacteriology laboratory for confirmation. Spoligotyping and mycobacterial interspersed repetitive unit-variable number tandem repeat analyses were performed for all the suspected isolates and all other isolates cultured on the same day as the five suspected isolates.

Results:  Three cases were confirmed as false-positive culture cases based on the laboratory investigation. The culture from one of these cases (index case 1) grew multidrug-resistant TB. Another patient (index case 2) received an extended course of anti-TB treatment after he was considered to have failed treatment because of the false-positive MTB culture result. No anti-TB medication was given for index case 3. All three cases with false-positive cultures had only one positive culture specimen among multiple consecutive specimens submitted for cultures. In addition, specimens of the false-positive cultures were all negative for acid-fast smears.

Conclusions:  False-positive MTB cultures should be suspected in the following situations: when growth is observed on only one specimen among multiple specimens submitted; when it is positive in only one culture medium, especially in broth; or when there is only one specimen submitted. False-positive MTB cultures can be further confirmed with modern molecular typing techniques.

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