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 (RA) of Escherichia coli and non-E. coli Enterobacteriaceae, 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, Citrobacter species, grouped as non-E. coli Enterobacteriacea (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 1.4-11.3) times higher than of E. coli, yielding single admission reproduction numbers (RA) of 0.17 (95% credibility interval 0.094-0.29) for non-EcE and 0.047 (0.018-0.098) for E. coli. Conclusions: In ICUs non-EcE, mainly being K. pneumoniae, are 3.7 times more transmissible than E.coli. Estimated RA values of these bacteria were below the critical threshold of one, suggesting that in these ICUs outbreaks typically remain small with current infection control policies