Investigation of Laboratory Cross- Contamination of Mycobacterium tuberculosis Cultures

Many clinicians and laboratory personnel are unaware that a culture positive for Mycobacterium tuberculosis may rep-resent 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. Fail-ure to recognize laboratory cross-contamination with M. tu-berculosis leads to both erroneous administration of unnec-essary medications and expenditure of resources required to conduct contact investigations. In July 1998, a hospital in Maryland contacted the Maryland Department of Health, who contacted the Centers for Diseas