The Transmissibility of Antibiotic-Resistant Enterobacteriaceae in Intensive Care Units.

Background. The global emergence of infections caused by Enterobacteriaceae resistant to expanded-spectrum cephalosporins (ESCs) in intensive care units (ICUs) is, at least partly, driven by cross-transmission. Yet, individual transmission capacities of bacterial species have not been quantified. Methods. In this post hoc analysis of a multicenter study in 13 European ICUs, prospective surveillance data and a mathematical model were used to estimate transmission capacities and single-admission reproduction numbers (R-A) of Escherichia coli and non-E. coli Enterobacteriaceae (non-EcE), all being ESC resistant. Surveillance was based on a chromogenic selective medium for ESC-resistant Enterobacteriaceae, allowing identification of E. coli and of Klebsiella, Enterobacter, Serratia, and Citrobacter species, grouped as non-EcE. Results. Among 11 420 patients included, the admission prevalence was 3.8% for non-EcE (74% being Klebsiella pneumoniae) and 3.3% for E. coli. Acquisition rates were 7.4 and 2.6 per 100 admissions at risk for non-EcE and E. coli, respectively. The estimated transmission capacity of non-EcE was 3.7 (95% credibility interval [CrI], 1.4-11.3) times higher than that of E. coli, yielding single-admission reproduction numbers (R-A) of 0.17 (95% CrI,.094-.29) for non-EcE and 0.047 (95% CrI,.018-.098) for E. coli. Conclusions. In ICUs, non-EcE, mainly K. pneumoniae, are 3.7 times more transmissible than E. coli. Estimated R-A values of these bacteria were below the critical threshold of 1, suggesting that in these ICUs outbreaks typically remain small with current infection control policies.