Misdiagnoses of tuberculosis resulting from laboratory cross-contamination of Mycobacterium tuberculosis cultures--New Jersey, 1998

Abstract

A diagnosis of tuberculosis (TB) is rarely disputed if Mycobacterium tuberculosis is isolated from a clinical specimen; however, specimen contamination may occur (1-3). Identification of TB strain patterns through molecular typing or DNA fingerprinting is a recent advancement in TB laboratory techniques (3-7). CDC's National Tuberculosis Genotyping and Surveillance Network (NTGSN) performs DNA fingerprinting on TB isolates to determine the frequency of clustering among M. tuberculosis strains in project surveillance sites. In November 1998, NTGSN detected 11 isolates from previously reported TB cases among persons in New Jersey whose DNA fingerprints matched the avirulent laboratory M. tuberculosis control strain H37Ra. H37Ra does not cause active TB in humans, but it has been reported as a source of cross-contamination (8). In collaboration with the New Jersey Department of Health and Senior Services, CDC investigated H37Ra as a possible cause of TB disease and/or TB misdiagnoses caused by laboratory cross-contamination in the 11 case-patients. This report describes findings from two of the 11 cases and summarizes the results of this investigation, which indicate that TB was misdiagnosed and demonstrate the value of DNA fingerprinting to identify occurrences of cross-contamination of patient specimens.