Used for surveillance to detect nasal colonization with Methicillin-resistant Staphylococcus aureus.

1. Antibiotic resistance is associated with excess morbidity and mortality as well as increased hospital costs.  The attributable mean costs of an MRSA bloodstream infection is substantial compared with that for a nosocomial MSSA blood stream infection (Infect Control Hosp Epidemiol.  1999; 20: 408-11).  
2. The control of these pathogens has been a priority of the Duke and Durham Regional Hospitals Infection Control Teams.  Contact isolation and diligent hand washing are the primary prevention strategies used to limit nosocomial transmission of MRSA.  Furthermore, methods that rapidly identify colonized patients have the potential to reduce nosocomial spread and are valuable in outbreak situations.
3. An Infection Control consultation is recommended when colonized patients are identified.  Call DUKE:684-5457, DURHAM REGIONAL:470-7171.

1. The test is FDA approved for nasal swabs only.  Order culture for all other specimen types.
2. Negative test results may occur from improper specimen collection, not following the recommended sample collection procedure, handling or storage, technical error, sample mix-up, or because the number of organisms in the specimen is not detected by the test. 
3. Positive test results do not necessarily indicate the presence of viable organism.  They are however, presumptive for the presence of MRSA.  The gene conferring resistance to methicillin (mecA) is contained within the targeted MRSA cassette.  False-positive results may occur in cases in which mecA has dropped-out of the cassette.
4. Mutations or polymorphisms in primer or probe binding regions may affect detection of new or unknown MRSA variants resulting in a false negative result.
5. Potentially interfering substances include blood, mucus, and nasal sprays used to relieve decongestion, nasal dryness, or irritation.

Cepheid Xpert MRSA Assay.  An FDA-cleared PCR test, the primers and probes in the Xpert MRSA assay detect a proprietary sequence for the presence of a cassette inserted into the Staphylococcus aureus chromosome.  The cassette typically contains the mecA gene.
Based on the manufacturer’s published test performance characteristics, the Xpert MRSA Assay has a 73% positive predictive value and a 98.8% negative predictive value when compared with the direct culture methods.  The limit of detection was determined to be 80 CFU per swab.