In the Journals

Costs, specificity top considerations when choosing commercial tests for MRSA infection control surveillance

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April 28, 2015

Three commercial real-time polymerase chain reaction tests performed similarly in detecting MRSA in nasal samples of hospitalized patients in a large surveillance program, according to research published in the American Journal of Clinical Pathology.

The cost of assay and specificity of results are among the most meaningful measures providers could consider when evaluating the cost benefit ratio of screening and impact on utilization of health care resources, according to researchers.

“One can maximize the benefit-to-cost relationship of a surveillance program for MRSA control by paying close attention to the specificity of the assay chosen, as well as the sensitivity,” Lance R. Peterson, MD, director of microbiology and infectious diseases research at NorthShore University HealthSystem in Evanston, Illinois told Infectious Disease News. “A high number of false positive tests (eg, lower specificity) can raise the number of patients placed into isolation precautions, which is costly for the healthcare system.”

Lance R. Peterson

Peterson and colleagues evaluated the LightCycler MRSA Advanced Test (Roche Molecular Diagnostics), the BD MAX MRSA assay (Becton Dickinson) and the Xpert MRSA assay (Cepheid) to detect MRSA nasal colonization using double-headed swabs (n = 27,647 specimens) collected from inpatients at admission and discharge.

One swab was plated onto a CHROMagar MRSA (Becton Dickinson) and broken off into a tryptic soy broth for enrichment. The culture broth was then incubated for 24 hours and plated to CHROMagar MRSA.

On the second swab, the molecular real-time polymerase chain reaction tests were performed. The researchers then analyzed the cost benefit ratio of screening to assess parameters affecting hospital resources.

The sensitivity and specificity was 98.3% and 98.9%, respectively, for the LightCycler MRSA Advanced Test and 95.7% and 98.8%, respectively, for the Xpert MRSA assay; the difference was not significant.

The LightCycler MRSA Advanced Test demonstrated a positive predictive value of 86.7%, followed by the Xpert MRSA assay at 82.7% and the BD MAX MRSA test at 72.2% (P < .001).

All three assays were cost-effective. The LightCycler MRSA Advanced Test showed the highest economic return.

“MRSA surveillance can be done with several FDA cleared molecular diagnostic assays having good sensitivity, but there are some differences in specificity that can impact the program cost beyond that of just the testing kit price,” Peterson said. “Continued research on lowering test cost and processing simplicity for MRSA surveillance to control this important organism can facilitate wider use of this important laboratory tool.” – by Allegra Tiver

For more information: Lance R. Peterson, MD, can be reached at NorthShore University HealthSystem, 2650 Ridge Avenue, Burch 116, Evanston, IL 60201; email: lpeterson@northshore.org.

Disclosure: Peterson reports receiving research grants from the Agency for Healthcare Research and Quality, BD-GeneOhm, CareFusion, Cepheid, GeneWeave, IMDx, MicroPhage, Nanosphere, National Institute of Allergy and Infectious Diseases, NIH, Roche, 3M and Washington Square Health Foundation for work in molecular diagnostics; as well as consulting for BD-GeneOhm, Cepheid, MicroPhage, Nanosphere and Roche in this area of research. Please see the full study for a list of all other authors’ relevant financial disclosures.

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