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Rapid MRSA testing did not reduce use of inappropriate antibiotics
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Implementing a rapid molecular diagnostic test for MRSA among patients with purulent skin infections did not reduce the empiric use of MRSA-active antibiotics for patients with non-MRSA infections, according to researchers from the University of California, Los Angeles.
“Delays in appropriate directed antibiotics are imposed by the timeliness of routine culture testing,” the researchers wrote in a brief report published in Clinical Infectious Diseases. “Whereas theoretical best practice use of the rapid PCR assay would have reduced the overall rate of discordant antibiotic use from 58% to 6.5%, even with physician education and active pharmacist guidance, we found only a non-statistically significant trend towards reduction to a rate of 45%.”
The researchers compared rates of discordant antibiotic use between three separate, consecutive phases. Phase 1 (March to August 2009) was before the assay was introduced. Phase 2 (September 2009 to March 2010) took place after ED physicians were instructed to order the rapid test for all patients with purulent skin infection, and physicians were encouraged to use results in antibiotic selection. In phase 3 (April to November 2010), a pharmacist was assigned during regular week day hours to track assay results and advise physicians on alternative antibiotics if necessary.
The study included 165 patients, and MRSA was isolated by culture in 47 of the patients: 15 of 53 in phase 1, 13 of 50 in phase 2 and 19 of 62 in phase 3. Methicillin-sensitive Staphylococcus aureus (MSSA) was detected in 11 phase 1 patients, 19 phase 2 patients and 23 phase 3 patients. Compared with standard culture, the PCR test was 100% sensitive and 89% specific for MRSA detection, and 100% sensitive and 68% specific for MSSA detection
In phase 1, 31 patients (58%) were treated with discordant antibiotics for a median duration of 0.6 days. In phase 2, 35 patients (58%) were treated with discordant antibiotics for a median of 1.1 days. In phase 3, 28 patients (45%) were treated with discordant antibiotics for a median of 0.2 days.
“If the PCR assay had been consistently used to guide antibiotic selection, the rate of discordant antibiotic use would have been reduced from 58% to 6.5%, with all MRSA-positive patients receiving appropriate antibiotics,” the researchers wrote.
Disclosure: Some of the researchers report various financial relationships with AstraZeneca, Cepheid, Cubist, Durata, Forest, Merck, Optimer and Trius. The study was supported by a grant from Cepheid, maker of the Xpert MRSA/SA SSTI assay.
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