Rapid VRE susceptibility tests may ease isolation
Shaving time off results may save money
New rapid diagnostic tests under development could help expedite patient isolation for vancomycin-resistant enterococci (VRE) by sharply cutting the time it takes to get drug susceptibility data, researchers report.
A fluorescent test under development by Becton Dickinson Microbiology Systems in Sparks, MD, can accurately detect resistance to gentamicin, streptomycin, vancomycin, and ampicillin for over 90% of the clinically important enterococci specimens in five hours, according to Susan O’Rourke, BS, research and development supervisor.
"It was very accurate for vancomycin resistance," she tells Hospital Infection Control. "E. facelis is the one that labs see maybe 90% of the time in a clinical setting. In my tests, all the E. facelis came up in five hours with the correct answers."
However, the test took 18 to 20 hours of incubation time to detect resistance in E. faecium strains, which account for approximately 8% of all enterococci isolated in the clinical setting and are more likely to be resistant to ampicillin and vancomycin than other species. The test method uses a fluorescent indicator that glows when viewed with a UV lamp if an organism is resistant to an antibiotic. The method is manual, and does not require additional tests to confirm antibiotic resistance. A total of 132 strains of enterococci received from clinical laboratories were tested, and the results were compared to results obtained with standard methods, which take 24 to 48 hours.
Patients may be placed in isolation pending the results of the tests, so faster detection of VRE could save money by eliminating isolation measures. Conversely, identifying VRE patients who are not in isolation could speed up the use of appropriate measures and help avert transmission to others.
"The reason we tried for an under-eight-hour test was so a laboratory clinician could run the test and report the results in the same working shift of the laboratory," O’Rourke says. "If a patient needed to be isolated, it could happen probably a day sooner than it would otherwise. It also would help identify the appropriate therapeutic antibiotic."
Data on the test which has yet to be released for marketing were unveiled in September at the annual Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC) in New Orleans.
Also presented at ICAAC were data on another rapid VRE test developed by IDEXX Laboratories in Westbrook, ME. The test comes as a powder in a test tube and is prepared for use by the addition of 5 mL of water just prior to inoculation. A swab from the environment, rectal, perirectal, or other body site is twirled directly in the liquid and the test is placed in an ambient incubator at 35 degrees C. The production of a bright pink color on the disk shows the presence of VRE.
According to data presented at ICAAC, the test accurately identified VRE in 76% of samples tested within 18 hours of incubation and 94% of the samples within 24 hours. At 28 hours of incubation, 100% of VRE-positive samples were detected and there were no false-positive results.
[Editor’s note: The IDEXX test has now been released for marketing, and information about cost and availability can be obtained by contacting the company at (800) 497-9206. For more information on the availability of the Becton Dickinson VRE test, contact the company at (800) 365-3321.]
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