Investigation of Laboratory cross-contamination of Mycobacterium tuberculosis cultures.

Many clinicians and laboratory personnel are unaware that a culture positive for Mycobacterium tuberculosis may represent contamination. Laboratory cross-contamination with the M. tuberculosis laboratory control strain (H37Ra) occurs infrequently and therefore demands heightened awareness and recognition. We report 3 occurrences of laboratory cross-contamination from the same laboratory. These occurrences illustrate the importance of interpreting laboratory results in conjunction with the patient's clinical presentation. Failure to recognize laboratory cross-contamination with M. tuberculosis leads to both erroneous administration of unnecessary medications and expenditure of resources required to conduct contact investigations.