INVESTIGATION OF A PSEUDO-OUTBREAK OF ORTHOPEDIC INFECTIONS CAUSED BYPSEUDOMONAS-AERUGINOSA

OBJECTIVE: To report a pseudoepidemic of Pseudomonas aeruginosa infect ions discovered during an investigation of postoperative joint infecti ons. DESIGN: A retrospective review of case patients' hospital charts, operative reports, and laboratory data, as well as environmental cult uring, polymerase chain reaction (PCR) ribotyping of outbreak isolates , and in vitro analysis of P aeruginosa growth characteristics. SETTIN G: A 510-bed, university-affiliated adult tertiary care hospital. RESU LTS: Between October 1 and December 1, 1992, seven postsurgical joint infections were diagnosed, including four caused by P aeruginosa. A bo ttle of ''sterile'' saline used to process tissue specimens was found to be contaminated with P aeruginosa. Further investigation revealed t hat P aeruginosa had grown from seven additional tissue cultures, all of which had been processed with the contaminated saline. PCR ribotype s of the contaminant matched those of the clinical isolates. In vitro, P aeruginosa strains were viable in commercial nonbacteriostatic sali ne, but never caused visible turbidity. Six patients received antibiot ics for their presumed infections; four patients had peripherally inse rted central catheters placed, and one experienced severe anaphylactic reactions to several antibiotics. CONCLUSIONS: Pseudoepidemics due to common organisms are often difficult to detect, and delayed recogniti on can result in substantial morbidity. This outbreak investigation il lustrates the potential for contamination of diluents in the microbiol ogy laboratory and emphasizes the need for meticulous quality control (Infect Control Hosp Epidemiol 1994;15652-657).