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Background: Automated testing instruments (ATIs) are commonly used by clinical microbiology laboratories to perform antimicrobial susceptibility testing (AST), whereas public health laboratories may use established reference methods such as broth microdilution (BMD). We investigated discrepancies in carbapenem minimum inhibitory concentrations (MICs) among Enterobacteriaceae tested by clinical laboratory ATIs and by reference BMD at the CDC. Methods: During 2016–2018, we conducted laboratory- and population-based surveillance for carbapenem-resistant Enterobacteriaceae (CRE) through the CDC Emerging Infections Program (EIP) sites (10 sites by 2018). We defined an incident case as the first isolation of Enterobacter spp (E. cloacae complex or E. aerogenes), Escherichia coli, Klebsiella pneumoniae, K. oxytoca, or K. variicola resistant to doripenem, ertapenem, imipenem, or meropenem from normally sterile sites or urine identified from a resident of the EIP catchment area in a 30-day period. Cases had isolates that were determined to be carbapenem-resistant by clinical laboratory ATI MICs (MicroScan, BD Phoenix, or VITEK 2) or by other methods, using current Clinical and Laboratory Standards Institute (CLSI) criteria. A convenience sample of these isolates was tested by reference BMD at the CDC according to CLSI guidelines. Results: Overall, 1,787 isolates from 112 clinical laboratories were tested by BMD at the CDC. Of these, clinical laboratory ATI MIC results were available for 1,638 (91.7%); 855 (52.2%) from 71 clinical laboratories did not confirm as CRE at the CDC. Nonconfirming isolates were tested on either a MicroScan (235 of 462; 50.9%), BD Phoenix (249 of 411; 60.6%), or VITEK 2 (371 of 765; 48.5%). Lack of confirmation was most common among E. coli (62.2% of E. coli isolates tested) and Enterobacter spp (61.4% of Enterobacter isolates tested) (Fig. 1A), and among isolates testing resistant to ertapenem by the clinical laboratory ATI (52.1%, Fig. 1B). Of the 1,388 isolates resistant to ertapenem in the clinical laboratory, 1,006 (72.5%) were resistant only to ertapenem. Of the 855 nonconfirming isolates, 638 (74.6%) were resistant only to ertapenem based on clinical laboratory ATI MICs. Conclusions: Nonconfirming isolates were widespread across laboratories and ATIs. Lack of confirmation was most common among E. coli and Enterobacter spp. Among nonconfirming isolates, most were resistant only to ertapenem. These findings may suggest that ATIs overcall resistance to ertapenem or that isolate transport and storage conditions affect ertapenem resistance. Further investigation into this lack of confirmation is needed, and CRE case identification in public health surveillance may need to account for this phenomenon.
We surveyed 399 US acute care hospitals regarding availability of on-site Legionella testing; 300 (75.2%) did not offer Legionella testing on site. Availability varied according to hospital size and geographic location. On-site access to testing may improve detection of Legionnaires disease and inform patient management and prevention efforts.
Carbapenem-resistant Enterobacteriaceae (CRE) are a growing problem in the United States. We explored the feasibility of active laboratory-based surveillance of CRE in a metropolitan area not previously considered to be an area of CRE endemicity. We provide a framework to address CRE surveillance and to monitor changes in the incidence of CRE infection over time.
To describe the implementation of a population-based surveillance system for multidrug-resistant gram-negative bacilli (MDR-GNB).
Population-based active surveillance by the Georgia Emerging Infections Program.
Metropolitan Atlanta, starting November 2010.
Residents with MDR-GNB isolated from urine or a normally sterile site culture.
Surveillance was implemented in 3 phases: (1) surveying laboratory antibiotic susceptibility testing practices, (2) piloting surveillance to estimate the proportion of GNB that were MDR, and (3) maintaining ongoing active surveillance for carbapenem-nonsusceptible Enterobacteriaceae and Acinetobacter baumannii using the 2010 Clinical and Laboratory Standards Institute (CLSI) breakpoints. Pilot surveillance required developing and installing queries for GNB on the 3 types of automated testing instruments (ATIs), such as MicroScan, in Atlanta's clinical laboratories. Ongoing surveillance included establishing a process to extract data from ATIs consistently, review charts, manage data, and provide feedback to laboratories.
Output from laboratory information systems typically used for surveillance would not reliably capture the CLSI breakpoints, but queries developed for the 3 ATIs did. In November 2010, 0.9% of Enterobacteriaceae isolates and 35.7% of A. baumannii isolates from 21 laboratories were carbapenem nonsusceptible. Over a 5-month period, 82 Enterobacteriaceae and 59 A. baumannii were identified as carbapenem nonsusceptible.
Directly querying ATIs, a novel method of active surveillance for MDR-GNB, proved to be a reliable, sustainable, and accurate method that required moderate initial investment and modest maintenance. Ongoing surveillance is critical to assess the burden of and changes in MDR-GNB to inform prevention efforts.
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