By the end of May 2010, an increase in the number of urine specimens that were culture positive for extremely drug-resistant (XDR) Pseudomonas aeruginosa was observed in our 800-bed university hospital. This led to an infection control alert. No epidemiological link between the patients and no increase in the frequency of XDR P. aeruginosa in non-urine samples were observed. Therefore, a pseudo-outbreak due to analytical contamination in the laboratory was rapidly suspected. A prospective and retrospective search of cases was initiated, and the sampling of the automated urine analyzers used in the laboratory was performed. Antibiotypes were determined by disc diffusion, and genotypes were determined by pulsed-field gel electrophoresis (PFGE). From February to July 2010, 17 patients admitted to 12 different departments and 6 outpatients were included. The mixing device of the cytometric analyzer used for the numeration of urinary particles (Sysmex UF1000i) proved to be heavily contaminated. Isolates recovered from 12 patients belonged to the same antibiotype and PFGE type as the isolate recovered from the analyzer. Extensive disinfection with a broad-spectrum disinfectant and the replacement of the entire tubing was necessary to achieve the complete negativity of culture samples taken from the analyzer. A pseudo-outbreak caused by an XDR P. aeruginosa clone was proven to be due to the contamination of the cytometric analyzer for urinary sediment. Users of such analyzers should be aware that contamination can occur and should always perform culture either before the processing of the urine sample on the analyzer or on a distinct sample tube.
Pseudomonas aeruginosa is a Gram-negative aerobic rodshaped bacterium that inhabits a wide range of environments, such as water, soil, the rhizosphere, and animals (11). It also is known as a frequent opportunistic pathogen in both animals and humans. Due to its potential for developing resistance against multiple antibiotic and antiseptic compounds, P. aeruginosa also has emerged as a major, difficult-to-treat nosocomial pathogen. P. aeruginosa is an important cause of morbidity and mortality in high-risk patients, such as immunosuppressed, cystic fibrosis, burn, cancer, and ventilated intensive care patients (11). To date, countless P. aeruginosa nosocomial outbreaks have been described that were caused by patient-topatient transmission, environmental sources, or contaminated medical devices (5,(8)(9)(10). P. aeruginosa also has been reported as a cause of pseudo-outbreaks due to the contamination of media used for clinical specimen collection, transport, or analysis (6, 12, 13).The Sysmex UF1000i is an automated fluorescence flow cytometer used to count and classify cells and particles in urine samples. This automated system, which has been used in our 800-bed university hospital laboratory since January 2010, is established as a rapid and sensitive screening method with high negative predictive value which avoids the unnecessary culture of negative urine samples and presen...