A case of Mycobacterium tuberculosis laboratory cross-contamination

Abstract Setting A laboratory cross-contamination event was suspected because Mycobacterium tuberculosis was unexpectedly detected at a high incidence in the cultures of several clinical specimens at the National Hospital Organization, Tokyo National Hospital, Japan. Objective To describe a case of Mycobacterium tuberculosis laboratory cross-contamination. Design We reviewed the medical records of 20 patients whose clinical specimens were suspected to have been contaminated by Mycobacterium tuberculosis . Variable number of tandem repeat analysis with 15 loci, the Japan Anti-Tuberculosis Association-12, and three additional hyper-variable loci, was performed to identify the cross-contamination event. Results The clinical, laboratory, and variable number of tandem repeat data revealed that the cross-contamination had possibly originated from one strongly positive specimen, resulting in false-positive results in 11 other specimens, including a case treated with anti-tuberculosis drugs. Conclusion Clinical and laboratory data must be re-evaluated when cross-contamination is suspected and variable number of tandem repeat analysis should be used to confirm cross-contamination. Furthermore, original isolates should be stored appropriately, without sub-culturing and genotyping should be performed at the earliest possible for better utilization of variable number of tandem repeat for the identification of cross-contamination.