Interpretive Data

LIMITATIONS:

• Results from the Xpert MRSA/SA SSTI Assay should be interpreted in conjunction with other laboratory and clinical data available to the clinician.
• The Xpert MRSA/SA SSTI Assay can detect MRSA and/or SA DNA from non-viable organisms. The probability of this occurring increases for patients on antibiotics. In the pivotal clinical study the false positive rate (relative to culture) of detecting SA in patents using antibiotics, within 3 weeks prior to Xpert MRSA/SA testing, was 13.8%. The false positive rate (relative to culture) of detecting MRSA in patients using antibiotics, within 3 weeks prior to Xpert MRSA/SA testing, was 9.5%.
• A positive test result does not necessarily indicate the presence of viable organisms. It is, however, presumptive for the presence of MRSA or SA.
• Testing with the Xpert MRSA/SA SSTI Assay should be used as an adjunct to other methods available.
• Erroneous test results might occur from improper specimen collection, failure to follow the recommended sample collection, handling and storage procedures, technical error, sample mix-up, or because the number of organisms in the specimen is too low to be detected by the test. Careful compliance with the instructions in this insert is necessary to avoid erroneous results.
• Because the detection of MRSA and SA is dependent on the number of organisms present in the sample, reliable results are dependent on proper specimen collection, handling, and storage.
• Mutations or polymorphisms in primer or probe binding regions may affect detection of new or unknown MRSA variants resulting in a false negative result.
• In samples containing both MRSA and SA, the Xpert MRSA/SA SSTI Assay may not detect the methicillin-resistant SA organisms. (In the pivotal clinical trial, the Xpert MRSA/SA SSTI Assay failed to detect 2 of 5 MRSA culture positive samples in situations with documented MRSA/SA mixed infections.)
• In a mixed culture, the analytical LoD of MRSA is variable when extremely high concentrations of SA are present. Competition from SA was observed at an MRSA:SA ratio of 1:1x106. In the Clinical studies, 5 of the 246 MRSA positive cultures had mixed infections of MRSA and SA. Xpert MRSA/SA SSTI identified 3 of the 5 mixed infections as MRSA positive and 2 of the 5 as SA positive/MRSA negative.
• Inhibition of the MRSA/SA SSTI Assay has been observed with the following substances: StaphA +Septic (5% w/v), Hydrocortisone (5% w/v), and antibacterial hand sanitizer (5% w/v).
• Samples containing Mercurochrome may not be used due to its fluorescent nature.
• The Xpert MRSA/SA SSTI Assay will generate a false positive MRSA result when testing a mixed infection SSTI specimen containing both methicillin-resistant coagulase-negative Staphylococcus (MRCNS) and empty cassette methicillin-sensitive Staphylococcus aureus (SA).