The accurate performance of the Vitek 2 GP67 card for detecting methicillin-resistant coagulase-negative staphylococci (CoNS) is not known. We prospectively determined the ability of the Vitek 2 GP67 card to accurately detect methicillin-resistant CoNS, with mecA PCR results used as the gold standard for a 4-month period in 2012. Included in the study were 240 consecutively collected nonduplicate CoNS isolates. Cefoxitin susceptibility by disk diffusion testing was determined for all isolates. We found that the three tested systems, Vitek 2 oxacillin and cefoxitin testing and cefoxitin disk susceptibility testing, lacked specificity and, in some cases, sensitivity for detecting methicillin resistance. The Vitek 2 oxacillin and cefoxitin tests had very major error rates of 4% and 8%, respectively, and major error rates of 38% and 26%, respectively. Disk cefoxitin testing gave the best performance, with very major and major error rates of 2% and 24%, respectively. The test performances were species dependent, with the greatest errors found for Staphylococcus saprophyticus. While the 2014 CLSI guidelines recommend reporting isolates that test resistant by the oxacillin MIC or cefoxitin disk test as oxacillin resistant, following such guidelines produces erroneous results, depending on the test method and bacterial species tested. Vitek 2 cefoxitin testing is not an adequate substitute for cefoxitin disk testing. For critical-source isolates, mecA PCR, rather than Vitek 2 or cefoxitin disk testing, is required for optimal antimicrobial therapy.T he detection of methicillin resistance (MR) in coagulase-negative staphylococci (CoNS) can be critically important for isolates from normally sterile sites. However, detection of MR CoNS is problematic and less reliable than the detection of MR Staphylococcus aureus (1, 2). Cefoxitin susceptibility testing has greatly improved the reliability of detecting MR S. aureus and, to a lesser extent, CoNS (3, 4). Current CLSI guidelines recommend the use of cefoxitin disk testing for detecting MR CoNS, with some evidence that cefoxitin MIC determination can serve the same purpose (3, 5). A number of studies have shown that cefoxitin disk testing of CoNS is generally sensitive but can be nonspecific (3, 4, 6, 7). The Vitek 2 (Vitek) antimicrobial susceptibility system utilizes a cefoxitin susceptibility screening assay that was previously reported to have a 98% sensitivity for MR and a 100% specificity for S. epidermidis but only 66% and 100% sensitivity and specificity, respectively, for S. hominis (6). This led our laboratory to perform cefoxitin disk testing for S. hominis isolates rather than rely on the Vitek cefoxitin test. In addition, when the Vitek oxacillin result was discordant from the Vitek cefoxitin result, cefoxitin disk testing was performed. We found, however, that there were a large number of discrepancies between the Vitek cefoxitin and disk cefoxitin tests. Over the period from January to December 2011, we encountered 25 Vitek cefoxitin-susceptible CoNS isolates t...

BackgroundHealthcare-associated infections (HAIs) and multidrug-resistant organisms (MDROs) remain critically important problems. Although copper has well-described antimicrobial properties, the impact of copper-impregnated linens on HAIs and MDROs in healthcare settings remains undefined.MethodsThis study was conducted in a 24-bed medical ICU and a 24-bed surgical ICU from 1/12/16 to 7/31/16. Six beds in each ICU were randomized to CottonX™ accelerated copper linens (flat sheet, fitted sheet, pillow cover, gown) (Argaman Technologies Ltd.) and 18 beds to regular linens. Patients were enrolled if they were in the ICU for ≥3 days and were followed prospectively for development of an HAI (including C. difficile infection) and/or MDRO from ICU day 3 through 2 days after ICU discharge. MDROs were defined as a new clinical culture (i.e., no culture with the same organism in the prior year) with methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, or ceftriaxone-resistant or carbapenem-resistant Enterobacteriaceae. A patient could be included more than once for distinct ICU stays (“episodes”).ResultsAmong 1,021 subjects, the median age was 61 and 448 (44%) were female. Of 1,205 total episodes, 678 (56%) were in the MICU, 527 (44%) were in the SICU, and 351 (29%) were randomized to copper rooms. There were no significant differences between study groups with regard to demographics, comorbidities, indwelling devices, or antibiotic use. The overall rate (per 1,000 patient-days) of the composite outcome (HAI or MDRO) was 11.66 and 15.44 in copper and non-copper episodes, respectively, [incidence rate ratio (IRR) = 0.76 (95% CI, 0.46, 1.19); P = 0.22]. Rates of HAIs were 10.26 and 10.41 for copper and non-copper episodes, respectively ([IRR (95% CI) = 0.99 (0.57, 1.64); P = 0.97]. Rates of MDROs were 3.73 and 6.51 for copper and non-copper episodes, respectively [IRR (95% CI) = 0.57 (0.23, 1.26); P = 0.15]. Results were consistent when stratified by type of ICU.ConclusionWhile not statistically significant, there was a nearly 50% lower rate of MDRO infection and colonization with use of CottonX™ accelerated copper linens, possibly in part due to decreases in environmental contamination. Future work should further explore the role of copper linens in reducing MDROs.Disclosures D. Pegues, DaVita / Total Renal Care: Consultant, Consulting fee.

Our study was initially designed to determine why there was such a poor correlation between cefoxitin disk testing and Vitek 2 system (Vitek 2) cefoxitin screen results for the coagulasenegative staphylococci (CoNS) tested in our laboratory. We found two main reasons for this, inappropriate susceptibility testing of Staphylococcus saprophyticus because urine isolates of CoNS were not identified to the species level and inaccuracy of Vitek 2 for the identification of methicillin resistance. The data for all isolates tested, including S. saprophyticus, were presented in the main body of the results because that represented our practice at the time. It is important to note that Vitek 2 does not require entry of the CoNS species identity for results to be reported, including those for methicillin resistance; a warning is issued about the possible use of an incorrect oxacillin susceptibility breakpoint, but no warning is issued about possibly incorrect cefoxitin screen test results.While exclusion of S. saprophyticus from the analysis of the performance of Vitek 2 improved the overall specificity of detection of methicillin resistance of CoNS from 60% to 84%, this did not improve test performance enough to meet clinical needs or to meet the FDA guidelines on test performance. Vitek 2 performance may be significantly better in other laboratories testing CoNS populations that are more like those used for the FDA submission. However, one other study reported Vitek 2 performance issues for the detection of methicillin-resistant CoNS (1), suggesting that our experience is not unique.Dunne and colleagues (2) suggest that our gold standard for methicillin resistance should have been the cefoxitin disk test. Unfortunately the performance of cefoxitin disk testing of CoNS is neither as sensitive nor as specific as is mecA PCR testing (1, 3-6). We believe that our reference test method is accurate and that it should be the preferred method for determining the ability of phenotypic methods to detect methicillin resistance of CoNS. REFERENCES