Stewardship / Resistance Scan for Dec 16, 2016

Community-associated CRE
Antibiotic de-escalation
Multidrug-resistant strep

Rare community-associated CRE reported in Colorado

Investigators with the Colorado Department of Public and Environment and the Centers for Disease Control and Prevention (CDC) are reporting community-associated cases of carbapenem-resistant Enterobacteriaceae (CRE) in patients without known risk factors.

In a paper today in the CDC's Morbidity and Mortality Weekly Report (MMWR), the investigators said that six of 10 patients identified with New Delhi metallo-beta-lactamase (NDM)-producing CRE from 2014 to 2016 lacked the known CRE risk factors: hospitalization outside the United States, recent admission to short-stay and long-term acute care hospitals, residence in long-term care facilities, surgical procedures, and having indwelling devices like catheters. This is noteworthy because CRE lacking these exposures are rare in the United States.

Among the six patients identified, two had traveled internationally, two had underlying medical conditions, one was pregnant, three had no underlying comorbidities, and three had antibiotic exposure prior to positive culture. All of the patients, who ranged in age from 20 to 85, were diagnosed with urinary tract infections.

There were no epidemiologic links among the six patients, nor were there links between these patients and eight patients in Colorado diagnosed with CRE during a 2012 hospital outbreak (most of whom had the known CRE risk factors). In addition, whole genome sequencing performed at CDC labs on the isolates from the recent patients and the 2012 patients confirmed that they did not share common strains or plasmids. Among seven of the recent isolates that underwent sequencing, only two Escherichia coli ST167 isolates appeared to be related.

Carbapenemases like NDM , which can reside on mobile plasmids and be transferred among bacterial species, are believed to contribute to the increasing transmission and regional spread of CRE. As of April 2016, the authors note, Colorado had reported the second highest number of NDM-producing CRE in the United States. The identification of community-associated strains of the multidrug-resistant bugs adds another layer of concern.

"The source for the community-associated strains is unknown, but might represent transmission of multiple NDM strains outside inpatient health care settings," the authors write. "The finding that six of 10 recent NDM-producing CRE are community-associated suggests that the epidemiology of CRE could be changing." 

The authors add that further surveillance is required to determine whether the pattern continues.
Dec 16 CDC MMWR Notes from the Field


Benchmarks for antibiotic de-escalation

A recent study in BMC Infectious Diseases suggests 72 hours could be a plausible benchmark for antibiotic de-escalation.

In the retrospective observational study, researchers reviewed the randomly selected medical records of 240 patients who received simultaneous piperacillin/tazobactam and vancomycin from January to December 2011 at Wake Forest Baptist Medical Center, an 885-bed tertiary medical center with an active antimicrobial stewardship program. Antibiotic de-escalation was defined as the use of narrower spectrum antibiotics or discontinuation of antibiotics after the initiation of piperacillin/tazobactam and vancomycin therapy.

Among the 240 patients studied, the most commonly documented indications were pneumonia and sepsis. Nearly two-thirds of the patients (151) had their antibiotic regimens de-escalated by 72 hours, and nearly three-quarters (175) by 96 hours. The most common antibiotics prescribed for de-escalation were moxifloxacin and ceftriaxone. The proportion of patients de-escalated by 96 hours with positive vs. negative cultures was roughly equal—71% and 72%, respectively.

Median length of stay was 4 days shorter in the de-escalated patients, and the difference in adjusted mortality was not significant (p = 0.82). But the authors note that these associations may be surrogate markers of overall clinical status and the severity of illness, which were not controlled for in the study.

"While this study provides one plausible benchmark for antibiotic de-escalation, further studies, including evaluations of antibiotic appropriateness and patient outcomes, are needed to inform decisions on potential benchmarks for antibiotic de-escalation," the authors write.
Dec 12 BMC Infect Dis research article


Multidrug-resistant strep on the rise in UK, Ireland

Researchers in the United Kingdom are reporting the rise of a multidrug-resistant, non-vaccine serotype of Streptococcus pneumonia in the UK and Ireland.

According to a study yesterday in Eurosurveillance, analysis of S pneumonia isolates collected by the surveillance programs of British Society for Antimicrobial Chemotherapy (BSAC) and Public Health England (PHE) has found that serotype 15A is becoming increasingly prevalent.

While prior to 2011 serotype 15A isolates were encountered sporadically, since 2011 they have been among the 10 most prevalent serotypes in BSAC/PHE invasive isolate/bacteremia surveillance. Among BSAC respiratory isolates, 15A was the most prevalent serotype in 2013/14 and 2014/15, comprising 9% to 11% of isolates. In addition, 15A represented 29% and 32% of S pneumonia referred to PHE for reference investigation in 2013 and 2014 (before 2008, it represented 0 to 4%). 

Unlike other rising pneumococcal serotypes identified, serotype 15A isolates were found to be commonly resistant or nonsusceptible to multiple antibiotics, including macrolides, clindamycin, tetracycline, and penicillin, with around one-third of isolates showing "triple resistance" (to macrolides and tetracycline together with intermediate penicillin resistance). Triple resistance was strongly associated with ST63 and its variants. While this is a concern for patient management, the authors note that S pneumoniae 15A remains susceptible to other agents, including moxifloxacin, cefotaxime, and ampicillin.

S pneumoniae 15A is not covered by the 13-valent pneumococcal conjugate vaccine. Its rise, the authors write, implies that conjugate vaccines "will face an ongoing game of 'catch-up'" and that expansion beyond a 13-valent formulation will be necessary in the future.
Dec 15 Eurosurveill report

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