Cross-contamination with Mycobacterium tuberculosis: an epidemiological and laboratory investigation.
OBJECTIVE
To investigate possible cross-contamination of laboratory specimens, as suggested by an increased incidence of newly diagnosed patients with tuberculosis, many of whom had all negative smears for acid-fast bacilli and only one positive Mycobacterium tuberculosis culture referred to as "negative smears, one positive" or NSOP.


METHODS
Medical-record reviews were performed for all patients with NSOP results diagnosed at this facility within a 9-month period. Laboratory logbooks were reviewed for all isolates processed; DNA fingerprinting was performed on available isolates.


RESULTS
Of 80 patients with NSOP results, 45 (56%) were found to have false-positive cultures resulting from laboratory contamination with H37Ra, an avirulent stock strain of Mycobacterium tuberculosis.


CONCLUSIONS
Laboratory cross-contamination resulted in the false diagnosis of tuberculosis in at least 45 individuals. Use of the Mycobacteria Growth Indicator Tube may have contributed to these contamination incidents by detecting small numbers of contaminating mycobacteria that may not have been detected with less sensitive media.
Nivin
B
B
Bureau of Tuberculosis Control, New York City Department of Health, New York, USA.
Fujiwara
P I
PI
Hannifin
J
J
Kreiswirth
B N
BN
D003951:Diagnostic Errors; D004866:Equipment Contamination; D005189:False Positive Reactions; D006801:Humans; D007753:Laboratories; D009169:Mycobacterium tuberculosis; D013048:Specimen Handling