Pseudo-outbreak of Pseudomonas aeruginosan and Serratra marcescens related to bronchoscopes

OBJECTIVE: To investigate an apparent outbreak involving simultaneous isolation of Pseudomonas aeruginosa and Serratia marcescens from bronchoalveolar lavage (BAL) samples. DESIGN: Retrospective and prospective cohort studies using chart review, environmental sampling, and ribotyping of all available isolates. Cleaning and disinfection procedures for the bronchoscopes were also evaluated. SETTING: A 380-bed private hospital in S (a) over tildeo Paulo, Brazil. PATIENTS: Forty-one patients who underwent bronchoscopic procedures between December 1994 and October 1996 and from whom P aeruginosa and S. marcescens were concomitantly isolated. Bronchoscopes and related items were microbiologically assessed. RESULTS: P aeruginosa and S. marcescens were simultaneously isolated from BAL samples 12.6% of the time (41 of 324) during the epidemic period versus 1.8% of the time (1 of 54) in the pre-epidemic period (P =.035). Ribotyping revealed two strains of P aeruginosa and one of S. marcescens that were isolated from BAL samples of patients with no signs of respiratory tract infection, suggesting a pseudo-outbreak. Evaluation of bronchoscope disinfection revealed that inappropriate methods were being used. Implementation of simple control measures resulted in a significant decrease in simultaneous isolation of these species. CONCLUSION: Prevention of pseudo-outbreaks requires meticulous use of preventive measures for infection-prone medical procedures.