Specimen Requirements

Stability

Days Performed

Sun - Sat

Turnaround Time

1 day

Methodology

Special Info

With patient's head tilted back, insert both dry swabs (leave attached to red cap) approximately 1-2 cm into one nostril. Rotate the swabs against the inside of the nostril for 3 seconds. Apply slight pressure with a finger on the outside of the nose to ensure good contact between the swabs and inside of the nose. Using the same swabs, repeat for the other nostril. Place the swabs into the transport tube (swabs should stay attached to the red cap). Make sure the red cap is tightly on the transport tube.

Clinical Info

This test detects Staphylococcus aureus (SA) and methicillin-resistant Staphylococcus aureus (MRSA) from nasal swabs to determine if the patient carries S. aureus in their normal microbiome. This test is only for nares specimens. Specimens other than nares require culture (SANSAL).

Clinical Limitation

The Staphylococcus aureus PCR test is a screening test for nasal carriage. A negative result does not preclude MRSA/SA colonization. Results from the Xpert SA Nasal Complete assay should be interpreted in conjunction with other laboratory and clinical data available to the clinician, and should be used as an adjunct to nosocomial infection control efforts to identify patients needing enhanced precautions. Results should not be used to guide or monitor treatment for MRSA or SA infections. 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. A positive test result does not necessarily indicate the presence of viable organisms. It is however, presumptive for the presence of MRSA or SA. The Xpert SA Nasal Complete assay positive result does not necessarily indicate intervention eradication failure since nonviable DNA may persist. A negative result following a previously positive test result may or may not indicate eradication success. The performance characteristics were not established for patients ≤ 21 years of age. 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 SA Nasal Complete assay may not detect the MRSA organisms. The pivotal clinical study included one sample with documented MRSA/SA mixed infection; the Xpert SA Nasal Complete assay successfully identified the sample as MRSA positive/SA positive. 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 a MRSA:SA ratio of 1:1×106 in 7 of 8 SCCmec types tested. For SCCmec type VIII, competition from SA was observed at a MRSA:SA ratio of 1:1×103. Inhibition of the SA Nasal Complete assay resulting in Invalid test results has been observed in the presence of inhaled nasal steroids Flonase and Nasonex in SA negative samples at concentrations greater than 5% v/v, and 10% v/v, respectively. Inhibition of the SA Nasal Complete assay resulting in false negative test results has been observed in the presence of inhaled nasal steroids Flonase and Nasonex in MRSA positive samples at concentrations greater than 1% (v/v) and 5% (v/v), respectively. The Xpert SA Nasal Complete assay may generate a false positive MRSA result when testing a mixed infection nasal specimen containing both methicillin-resistant coagulase-negative Staphylococcus and empty cassette SA. The Xpert SA Nasal Complete assay may generate false negative MRSA results when testing borderline oxacillin resistant S. aureus (BORSA). The mechanism of oxacillin resistance in BORSA strains is due to an increased production of ß-lactamases, not the mecA gene. BORSA with oxacillin MICs of 4 – 8 µg/mL are considered borderline resistant but would be reported as MRSA negative by the Xpert SA Nasal Complete assay. BORSA strains are rare in the United States.The Xpert SA Nasal Complete assay may generate false negative MRSA results when testing modified S. aureus (MOD-SA). The mechanism of oxacillin resistance in MOD-SA strains is due to changes in affinity of penicillin binding proteins for oxacillin, not the mecA gene. MOD-SA with oxacillin MICs of 4 – 8 µg/mL are considered borderline resistant but, would be reported as MRSA negative by the Xpert SA Nasal Complete assay. MOD-SA strains are rare in the United States. There may be an association with false positive results in specimens containing blood. As with all PCR based in vitro diagnostic tests, extremely low levels of target below the LoD of the assay may be detected, but results may not be reproducible.

Reflex Tests

The following additional test(s) may be ordered depending on results:

• Staphylococcus aureus & MRSA Screen, Culture, Skin