Sputum Induction Problems Identified Through Genetic Fingerprinting

OBJECTIVE: To identify the contamination source of a cluster of eight positive Mycobacterium tuberculosis isolates from one laboratory session.METHODS: Spoligotyping was performed on M. tuberculosis isolates processed during one laboratory session. Laboratory and sputum induction protocols and records were reviewed. Sputum induction staff were interviewed. An environmental assessment of the sputum induction booth was performed.RESULTS: Spoligotyping identified a unique strain of susceptible M. tuberculosis from five induced sputa collected at Clinic A on the same day. Three specimens processed concurrently from other clinics had spoligotypes different from each other and from the cluster strain. A laboratory investigation revealed no procedural lapses. Sputum induction records from Clinic A indicated that patient 1 in the sputum induction booth had prior culture-confirmed tuberculosis. Patient 2 had a history of a drug-resistant strain. Patient 3 had completed tuberculosis treatment with positive cultures 7 months earlier. Patients 4 and 5 were new to the clinic and had no subsequent positive M. tuberculosis specimens. The sputum induction booth was working within normal parameters. Sputum induction that day was overseen by a new employee with limited training and no supervision. A review of the sputum induction protocol identified ambiguity regarding care of the ultrasonic nebulizer between patients, which may have led to reuse of the discarded nebulizer solution from patient 1.CONCLUSIONS: A break in the sputum induction protocol may have contributed to contamination of patient specimens. Sputum induction is complicated, mandating adequate staff training and supervision and patient preparation. Spoligotyping identified a potential source of M. tuberculosis contamination.