CROSS-CONTAMINATION WITH MYCOBACTERIUM-TUBERCULOSIS - AN EPIDEMIOLOGIC AND LABORATORY INVESTIGATION

OBJECTIVE: To investigate possible cross-contamination of laboratory s pecimens, as suggested by an increased incidence of newly diagnosed pa tients with tuberculosis, many of whom had all negative smears for aci d-fast bacilli and only one positive Mycobacterium tuberculosis cultur e referred to as ''negative smears, one positive'' or NSOP. METHODS: M edical-record reviews were performed for all patients with NSOP result s diagnosed at this facility within a 9-month period. Laboratory logbo oks were reviewed for all isolates processed; DNA fingerprinting was p erformed on available isolates. RESULTS: Of 80 patients with NSOP resu lts, 45 (56%) were found to have false-positive cultures resulting fro m laboratory contamination with H37Ra, an avirulent stock strain of My cobacterium tuberculosis. CONCLUSION: Laboratory cross-contamination r esulted in the false diagnosis of tuberculosis in at least 45 individu als. Use of the Mycobacteria Growth Indicator Tube may have contribute d to these contamination incidents by detecting small numbers of conta minating mycobacteria that may not have been detected with less sensit ive media.