Chest · 2009
Molecular evidence of false-positive cultures for Mycobacterium tuberculosis in a Taiwanese hospital with a high incidence of TB.
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Lai Chih-Cheng, Tan Che-Kim, Lin Sheng Hsiang, Liao Chun-Hsing, Chou Chien-Hong, Huang Yu-Tsung, Hsueh Po-Ren
Аннотация
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.
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.