Infections caused by carbapenem-nonsusceptible Enterobacteriaceae and extended-spectrum beta-lactamase (ESBL) Enterobacteriaceae increased from 2013 to 2017, according to a study published in BMC Infectious Diseases. During the same period, decreases were observed in multidrug-resistant (MDR) and carbapenem-nonsusceptible Acinetobacter species isolates and MDR Enterobacteriaceae.

This retrospective, large-scale study included over 1 million nonduplicate Enterobacteriaceae isolates collected from patients in 411 hospitals between 2013 and 2017. Antimicrobial susceptibility was assessed for over 1 million samples of 5 gram-negative bacterial groups: carbapenem-nonsusceptible Enterobacteriaceae, carbapenem-nonsusceptible Acinetobacter species, MDR Enterobacteriaceae, MDR Acinetobacter species, and ESBL Enterobacteriaceae. As a result of non-Gaussian features in the time series data, the study researchers used the unobserved component model for time series analysis to estimate trends in resistance patterns. Primary outcomes included trends in bacterial nonsusceptibility or resistance per 100 hospital admissions, as well as the quarterly ratio of resistant isolates to total nonduplicate isolates.

During the study period, the sample of Enterobacteriaceae isolates was found to contain 12.05% ESBL, 1.21% carbapenem-nonsusceptible, and 7.08% MDR. Further, urine cultures demonstrated the majority of resistant isolates: 66.66% were ESBL, 45.87% were carbapenem-nonsusceptible, and 63.04% were MDR. Among 19,325 Acinetobacter species isolates, 47.66% were MDR and 37.48% were carbapenem-nonsusceptible, with respiratory cultures being the most common source of resistant isolates for MDR (39.29%) and carbapenem-nonsusceptible (39.94%), followed by skin/wounds (36.04% vs 36.08%, respectively).

The rate of antibiotic-resistant ESBL Enterobacteriaceae per 100 admissions increased by an average slope of 0.0089 per quarter between 2013 and 2017 (P <.0001), and carbapenem-nonsusceptible Enterobacteriaceae increased by an average slope of 0.0004 per quarter (P=.0047); proportional trends in resistant pathogens were similar.

Conversely, a decrease was observed for both MDR (-0.00134 per quarter; P <.0001) and carbapenem-nonsusceptible (-0.0009 per quarter; P <.0001) Acinetobacter species between 2013 and 2017, with similar trends in proportions of resistant isolates. Researchers also demonstrated that compared with summer, winter was associated with higher resistance rates of MDR Enterobacteriaceae and MDR and carbapenem-nonsusceptible Acinetobacter species.

Limitations to these findings included the inability to assess clinical outcomes related to the study’s antibiotic-resistant pathogens, the exclusive use of nonduplicate cultures, a lack of investigation of resistance mechanisms, and variability between facilities with respect to susceptibility.

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Researchers concluded that these findings indicated that “increasing numbers of infections due to ESBL and [carbapenem-nonsusceptible] Enterobacteriaceae between 2013 and 2017,” underscoring the importance of efforts by the World Health Organization and the United States Center for Disease Control and Prevention to reduce their spread and fight antibiotic resistance in pathogens. Acinetobacter poses a particularly notable threat because of the difficulty associated with successful treatment, though decreases have been observed in both carbapenem-nonsusceptible and MDR Acinetobacter species.

Disclosure: This clinical trial was supported by Tetraphase Pharmaceuticals. Please see the original reference for a full list of authors’ disclosures.


Gupta V, Ye G, Olesky M, Lawrence K, Murray J, Yu K. Trends in resistant Enterobacteriaceae and Acinetobacter species in hospitalized patients in the United States: 2013–2017 [published online August 23, 2019]. BMC Infect Dis. doi: 10.1186/s12879–019–4387–3