Carbapenem-Resistant Gram-Negative Pathogens Among Hospitalized Patients in the United States Between 2010 and 2015

Abstract

Background. The spread of carbapenem-resistant (CR) Gram-negative bacteria is a public health concern. We investigated the frequency of CR A. baumannii, K. pneumoniae, P. aeruginosa, and E. coli infections in US hospitals from 2010 to 2015 and associated in-hospital mortality. Methods. Hospitalized patients with laboratory-confirmed infection with at least one of these pathogens were identified from the Premier Healthcare Database. CR and carbapenem-susceptible (CS) cohorts were identified based on carbapenem susceptibility data, where CR was defined as non-susceptible (resistant or intermediate) to at least one carbapenem. The primary outcome was the rate of carbapenem resistance by pathogen for each infection site (respiratory, blood, urine and other). Descriptive statistics were used to show the proportion of CR and associated crude in-hospital mortality for each pathogen and infection site cohort by calendar year and for the overall study period. Results. From 1 October 2010 to 30 September 2015, the proportion of patients whose culture sample had Gram-negative pathogens ranged from 36.3% to 39.9% in each calendar year (mean 37.9%); of these, 3.7% to 4.6% (mean 4.2%) were CR. However, 45% of A. baumannii and 19% of P. aeruginosa were CR, compared to only 1% of Enterobacteriaceae. Each year, 80.7% to 86.4% (mean 82.6%) of CR infections were caused by A. baumannii or P. aeruginosa while only 16% to 22% (mean 20%) were caused by K. pneumoniae or E. coli. Crude in-hospital mortality rates were higher in the CR cohorts than the CS cohorts, especially for A. baumannii blood stream infections (41.4% in CR versus 13.1% in CS). Crude in-hospital mortality rates by CR pathogens for all infection sites were 13.8% for A. baumannii, 9.4% for P. aeruginosa, 10.3% for K. pneumoniae and 6.8% for E. coli. Among patients who died with CR infections, 23.5% had A. baumannii and 59.5% had P. aeruginosa. Conclusion. A. baumannii and P. aeruginosa accounted for a far greater number of CR infections than K. pneumoniae and E. coli. This trend is consistent over time. CR infections were associated with higher crude mortality rates (i.e. not adjusted for other patient factors). When considering the disease burden of CR infections, CR A. baumannii and CR P. aeruginosa are the organisms of greatest impact.