LABORATORY CONTAMINATION OF MYCOBACTERIUM-TUBERCULOSIS CULTURES

The purpose of this study was to investigate possible laboratory conta mination of Mycobacterium tuberculosis cultures which resulted in the misdiagnosis of tuberculosis. We have investigated three cases in whic h a patient's culture was positive for M. tuberculosis but there was n ot a high clinical suspicion for disease. In each instance, another pa tient with clinically obvious pulmonary tuberculosis had specimens cul tured concurrently within the same clinical laboratory. The isolates f rom both the obvious cases of tuberculosis and the suspect cases were obtained through the State of Alabama TB Laboratory, but these isolate s originated at a commercial laboratory, a community hospital laborato ry, and at a university hospital. MTB isolates were fingerprinted by p robing for the insertion sequence IS6110. With each of the three pairs of isolates (case and suspicious case), identical IS6110 banding patt erns were found suggesting identical MTB strains. Because the patients were geographically separated, it is strongly suspected that laborato ry contamination of M. tuberculosis cultures resulted in the three sus pect cases being diagnosed with tuberculosis. These findings indicate that positive M. tuberculosis cultures resulting from laboratory conta mination can occur.