Pseudo-outbreak of Pseudomonas aeruginosa and Serratia 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 São 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.