Infection control personnel performing surveillance activities noticed a cluster of patients with isolates of carbapenem-resistant Pseudomonas aeruginosa (CRPA) in the surgical intensive care unit (SICU) of a German University Hospital. An outbreak investigation including a descriptive analysis, a case-control study comparing 15 CRPA case patients with 18 patients with carbapenem-susceptible P. aeruginosa, environmental sampling and pulsed-field gel electrophoresis (PFGE) typing of P. aeruginosa isolates was carried out. Fifteen patients acquired CRPA in the SICU during the outbreak period between 1 July 2006 and 31 October 2006 and PFGE typing of 11 available patient isolates revealed two outbreak strains as well as sporadic CRPA isolates. Both outbreak strains were resistant to penicillins, cephalosporins, carbapenems, aminoglycosides and quinolones, and remained susceptible only to colistin. The most likely mode of transmission was cross-transmission between patients during postoperative wound care with abdominal and/or thoracic drains (odds ratio: 64.33; 95% confidence interval: 5.32-999) and therapy with quinolones (48.37; 3.71-999) being independent risk factors for acquisition of CRPA. No further clusters of CRPA cases were observed after implementation of contact isolation precautions and after healthcare workers were made aware of the likely mode of transmission. This study shows the complex epidemiology of CRPA in a SICU including cross-transmission of two CRPA strains related to postoperative wound care.
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