Background: We noticed a sudden increase in the isolation of Klebsiella oxytoca from bronchial washing specimens during May to June 2006. An epidemiological investigation was conducted to identify the cause of the outbreak and to implement appropriate infection control measures. 

Methods: A total of 18 isolates of K. oxytoca were found. The 14 bronchial washing specimens that yielded K. oxytoca were taken in the outpatient bronchoscopy suite, and the other 4 specimens were obtained by a portable bronchoscopy. The medical records and microbiologic findings of these patients were reviewed. Environmental samples from two bronchoscopes and the bronchoscopy suite were cultured. The relations between the available 10 isolates from bronchial washing fluid were investigated by pulsed-field gel electrophoresis (PFGE). 

Results: No patients were judged to have had true infections attributable to K. oxytoca either before or after bronchoscopy. Cultures of samples from two bronchoscopes and related environment did not grow K. oxytoca. The PFGE analysis showed that 8 of 10 isolates had a similar pattern of DNA fragments. An infection control strategy was implemented, including adequately cleaning and disinfecting the bronchoscopes, and a sharp reduction in the incidence of K. oxytoca from bronchial washing samples followed. 

Conclusion: The sudden increase of K. oxytoca from bronchial washing specimens was a pseudo-outbreak. We presumed that the bronchoscopes became contaminated during a procedure in a patient colonized with K. oxytoca in the upper-respiratory tract. (Korean J Clin Microbiol 2008;11:5-10)