On November 1, 2013, acute and long-term healthcare facilities and laboratories began mandated CRE reporting to the Illinois Extensively Drug-Resistant Organism (XDRO) registry. CRE are identified by healthcare facilities based on local laboratory test results; however, many laboratories may have limited capacity to accurately detect CRE. This project provided additional reference laboratory testing to evaluate local laboratory capacity to identify CRE.
METHODS:
From December 3, 2014 to July 31, 2015, Illinois laboratories were asked to submit up to five CRE isolates to Illinois Department of Public Health (IDPH). Isolates were then forwarded to the clinical microbiology laboratory at Rush University Medical Center to perform validation testing against the Illinois CRE surveillance definition’s three criteria: a positive molecular test for carbapenemase (e.g., PCR), phenotypic test for carbapenemase (e.g., Modified Hodge Test), or (for Klebsiella and E. coli only) antibiotic susceptibility test results (non-susceptible to doripenem/meropenem/imipenem and resistant to all 3rd-generation cephalosporins). Results from Rush were compared to corresponding results reported by the submitting clinical laboratory.
RESULTS:
Fifty-six laboratories submitted 194 isolates to IDPH and Rush for validation. Of the 194 submitted specimens, 158 (81%) fulfilled at least one of the three CRE surveillance criteria based on Rush testing. PCR testing was performed on all isolates at Rush and 157 (81%) were found to carry a gene encoding a carbapenemase: 147 (94%) Klebsiella pneumoniae carbapenemase (KPC), 7 (4%) New Delhi metallo-beta-lactamase (NDM), and 3 (2%) OXA-48. Susceptibility testing was performed on all isolates, and 140 (72%) met the antibiotic susceptibility testing criterion. Reasons for specimens not meeting the CRE surveillance criteria included: an organism other than E. coli or Klebsiella being submitted based on susceptibility results (n=8), a non-Enterobacteriaceae submitted as CRE (n=4), or having a positive phenotypic result at the local laboratory but, at Rush, were PCR-negative and lacked antibiotic susceptibility criteria (n=17).
CONCLUSIONS:
The majority of submitted isolates were correctly identified as CRE. Reference laboratory testing identified 2 OXA-48-producing Enterobacteriaceae that would have otherwise not been recognized. Some isolates thought to be CRE by laboratories did not meet the Illinois surveillance definition; a proportion of these isolates may have lost their resistance mechanism over time or after repeated subculture, or the local laboratory did not follow the criteria accurately. To ensure high quality of mandatory CRE reporting, the XDRO registry includes decision support at the time of submission to avoid basic errors (e.g., reporting non-Enterobacteriaceae or mis-applying antibiotic criteria).