Investigation of a Pseudo-Outbreak of Orthopedic Infections Caused byPseudomonas aeruginosa

Abstract

AbstractObjectives:To report a pseudoepidemic ofPseudomonasaeruginosa infections discovered during an investigation of postoperative joint infections.Design:A retrospective review of case patients’ hospital charts, operative reports, and laboratory data, as well as environmental culturing, polymerase chain reaction(PCR)ribotyping of outbreak isolates, and in vitro analysis ofPaeruginosa growthcharacteristics.Setting:A 510-bed, university-affiliated adult tertiary care hospital.Results:Between October 1 and December 1, 1992, seven postsurgical joint infections were diagnosed, including four caused byP aeruginosa.A bottle of “sterile” saline used to process tissue specimens was found to be contaminated withP aeruginosa.Further investigation revealed thatP aeruginosahad grown from seven additional tissue cultures, all of which had been processed with the contaminated saline. PCR ribotypes of the contaminant matched those of the clinical isolates. Invitro, P aeruginosastrains were viable in commercial nonbacteriostatic saline, but never caused visible turbidity.Six patients received antibiotics for their presumed infections; four patients had peripherally inserted central catheters placed, and one experienced severe anaphylactic reactions to several antibiotics.Conclusions:Pseudoepidemics due to common organisms are oftendifficultto detect, and delayed recognition can result in substantial morbidity.Thisoutbreak investigation illustrates the potential for contamination of diluents in the microbiology laboratory and emphasizestheneed for meticulous quality control.