Epidemiological Surveillance of P. aeruginosa

From 2010 to 2014, P. aeruginosa isolates were collected from patients and environment from the five ICUs of the University Hospital of Lausanne. All consecutive patients hospitalized in the ICU with a clinical sample growing P. aeruginosa at any site were considered. No routine screening of P. aeruginosa carriage was performed. Based on colony morphology, one or several P. aeruginosa isolates per clinical sample were chosen for further typing analysis. For patients with prolonged ICU stays, multiple samples were considered for isolate recovery. In 2012, the ICU environment was investigated for the presence of P. aeruginosa. Tap water samples and environmental swabs obtained from taps and sink traps of all ICU rooms, as well as from the environment of the hydrotherapy room (including shower trolleys and shower mattresses), were analyzed. Thereafter, sink traps were investigated twice a year.
All isolates were typed by the double locus sequence typing (www.dlst.org) method as previously described (1 (link)). Three major DLST types, i.e., types with the highest number of patients, were further analyzed in this study: DLST 1–18 (24 patients), 6–7 (21 patients), and 1–21 (16 patients). For WGS, at least one isolate was selected per patient. If several isolates were collected from one patient, only isolates sampled 15 days apart were selected, unless they belonged from different sample sites. All environmental isolates from the three genotypes (mainly from sink traps) were included. A total of 74 DLST 1–18 isolates (56 clinical and 18 environmental), 50 DLST 6–7 isolates (35 clinical and 15 environmental), and 31 DLST 1–21 isolates (18 clinical and 13 environmental) were selected for WGS. Epidemiologic and genetic data of all clinical and environmental isolates are listed in Table S1.