Mycobacterium avium complex endocarditis: spurious diagnosis resulting from laboratory cross contamination

Contamination between specimens within clinical microbiology laboratories may be responsible for spurious outbreaks of mycobacterial infections. We report the case of a patient who had culture-negative endocarditis and whose cardiac tissue obtained at surgery yielded Mycobacterium avium complex (MAC). Epidemiologic investigation suggested cross contamination probably occurred during processing of the sputum specimens of a patient with pulmonary MAC disease and the cardiac samples from our patient; molecular strain typing showed the isolates from both patients to be identical. When mycobacterial infection rates increase or an unexpected case of mycobacterial infection occurs, the clinician should be alert to the possibility of cross contamination in the laboratory as a possible explanation.