Carbapenem-Resistant Enterobacteriaceae: Emerging Threat

Lara C. Pullen, PhD

October 06, 2015

The incidence of carbapenem-resistant enterobacteriaceae (CRE) is now at 2.93 per 100,000 population, according to the Centers for Disease Control and Prevention. Their seven-state population- and laboratory-based surveillance isolated most CRE cases from urine sources and revealed that CRE was associated with a high prevalence of prior hospitalizations or indwelling devices, as well as discharge to long-term care settings.

Alice Y. Guh, MD, MPH, from the Centers for Disease Control and Prevention in Atlanta, Georgia, and colleagues published their surveillance data online October 5 in JAMA. Their surveillance system included seven US geographical areas but was not designed to be representative of the United States. Case definition relied on locally performed susceptibility testing.

The investigators reported 599 incident CRE cases during the 2-year surveillance period. The authors estimate that the overall crude incidence of CRE infection is 2.93 per 100,000 population. They emphasize, however, that, as not all commercial laboratories serving the catchment area participated in the study, this number may underestimate the CRE burden of the areas.

The majority of CRE cases (86.8%; 95% confidence interval, 84.1% - 89.5%) were isolated from urine, and 11.4% (95% confidence interval, 8.8% - 13.9%) of cases were isolated from blood.

More than half (65.5%) of the cases were found in the outpatient setting among individuals who had been hospitalized within 30 days after their initial culture.

Many cases (33.9%) were also collected in a short-stay acute care hospital. In contrast, about 8% of cases were identified in individuals who did not have any documented healthcare exposure before the positive culture for CRE. "[H]owever, the extent to which these cases represent community-associated CRE compared with undocumented health care exposures is not clear. The possible spread of CRE from health care settings into the community, as has been recognized with other resistant gram negative bacilli, is a concerning prospect requiring further evaluation," the authors write.

In most cases, patients were hospitalized at approximately the same time as the positive CRE culture. Approximately half (55.9%) of patients survived the infection.

The investigators note variability in CRE incidence and frequency across different Emerging Infections Program sites. These results suggest that CREs are emerging and that control interventions have the potential to result in a substantial effect. The Centers for Disease Control and Prevention recommends that contact precautions be taken to prevent further spread of all CRE.

The surveillance data also revealed the presence of different types of CRE in different surveillance areas, suggesting an awareness of local epidemiology may help tailor prevention efforts in specific regions of the United States.

"The study by Guh et al represents an important step forward for CRE control in the United States. Expansion of surveillance to more geographic regions, including rural settings and metropolitan areas known to have high prevalence of CRE, would provide a more complete picture of the US burden. Molecular characterization of isolates would also inform prevention efforts," Mary K. Hayden, MD, from Rush University Medical Center in Chicago, Illinois, writes in an accompanying editorial.

The authors point out that the crude incidence of CRE is currently substantially lower than that of other drug-resistant organisms, such as Staphylococcus aureus (25.1 per 100 000 population) and Clostridium difficile (147.2 per 100 000). The low CRE incidence "highlights that CRE are emerging and suggests that control interventions implemented now could have a substantial effect," they write.

They note that surveillance results were limited by the ability of the surveillance definition to differentiate between urinary isolates that represented a true infection and those that did not. In addition, the definition for carbapenem nonsusceptibility did not include ertapenem, and thus the surveillance did not capture organisms that were nonsusceptible to only ertapenem.

The authors and Dr Hayden have disclosed no relevant financial relationships.

JAMA. Published online October 5, 2015. Article full text, Editorial full text

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