Rare but resistant and deadly strains of Enterobacteriaceae increasing

Rare but deadly strains of carbapenem-resistant Enterobacteriaceae (CRE) are on the rise, stated a report in the March 5 news brief from MMWR.

Last year, 4.6% of acute care hospitals reported at least one CRE infection (short-stay hospitals, 3.9%; long-term acute care hospitals, 17.8%). CRE strains were defined as E. coli, Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter cloacae, or Enterobacter aerogenes that were not susceptible to imipenem, meropenem or doripenem.

The proportion of Enterobacteriaceae that were resistant increased from 1.2% in 2001 to 4.2% in 2011 in the National Nosocomial Infection Surveillance system (NNIS)/National Healthcare Safety Network (NHSN) and from 0% in 2001 to 1.4% in 2010 in The Surveillance Network–USA (TSN). Most of the increase was observed in Klebsiella species (from 1.6% to 10.4% in NNIS/NHSN).

During the first six months of 2012, among the 3,918 U.S. acute care hospitals performing surveillance for either catheter-associated urinary tract infections or central-line-associated bloodstream infections in any part of their hospital, 181 (4.6%) reported one or more infections with CRE, 145 (3.9%) in short-stay hospitals and 36 (17.8%) in long-term acute care hospitals. Hospitals most affected were larger facilities and teaching hospitals in the Northeast.

To determine characteristics of CRE culture-positive episodes, researchers used data collected during the internally funded pilot of a population-based CRE surveillance project conducted through the Centers for Disease Control and Prevention's Emerging Infections Program (EIP) at three sites (Atlanta; Minneapolis-St. Paul; and Portland, Ore. metropolitan areas). Laboratories were asked for reports of CRE, defined as Enterobacteriaceae from sterile-site and urine cultures that were nonsusceptible to imipenem, meropenem or doripenem and resistant to all third-generation cephalosporins such as ceftriaxone, cefotaxime and ceftazidime. CRE-positive clinical cultures were classified as hospital-onset if the culture was taken from a hospital inpatient after the third day of admission. A health care exposure was defined as a recent hospitalization, long-term care admission, surgery, dialysis, or the presence of an indwelling device in the two days before the positive culture.

During the 5-month EIP project pilot, 72 CRE were identified in 64 patients, 56 patients with one positive culture and eight with two. Most came from the Atlanta metropolitan area (n=59), followed by Minneapolis-St. Paul (n=10) and Portland (n=3). Most CRE were Klebsiella species (n=49) followed by Enterobacter species (n=14) and E. coli (n=9). The most common source was urine (89%), followed by blood (10%). Most isolates were from cultures collected outside of acute care hospitals (47 of 71); however, most of these community-onset isolates were from patients with health care exposures (41 of 47), particularly recent hospitalizations (72%).

Although CRE are increasing in prevalence, their distribution is limited, the researchers noted. But resistant strains are associated with mortality rates exceeding 40%, which is significantly higher than mortality rates observed for carbapenem-susceptible Enterobacteriaceae.

“The high proportion of [long-term acute care hospitals] with CRE in 2012 highlights the need to expand prevention outside of short-stay acute-care hospitals into settings that, historically, have had less developed infection prevention programs,” the researchers wrote. “Additional research is needed to clarify unanswered questions, including assessing which CRE prevention strategies are most effective and investigating new prevention approaches such as decolonization. Fortunately, many regions are in a position to prevent the further emergence of these organisms if they act aggressively.”