Clinical Significance

Methicillin-Resistant Staphylococcus Aureus (MRSA) is a major cause of healthcare-acquired infections. Most transmissions occur in healthcare institutions as a result of contamination of the hands of healthcare workers, or from the healthcare environment which has been contaminated from patients carrying MRSA. While MRSA may cause infection with clinical manifestations ranging from pustules to sepsis and death. it can also be found in the nose or on the skin of individuals (asymptomatic carriers). Treatment of MRSA infections has become challenging as MRSA is frequently resistant to a broad range of animicrobial agents. Risk factors for infection with MRSA in healthcare settings include prolonged hospital stay, proximity to patients infected or colonized with MRSA, colonization with other resistant organisms scuh as vancomycin-resistant Enterococci (VRE) and Clostridium difficile, exposure to multiple and/or prolonged broad-spectrum antibiotic treatments, exposure to high MRSA prevalence areas within the healthcare facility, and prior MRSA infection or nasal carriage. Early identification of patients with MRSA nasal carriage can be part of an effective infection prevention program for MRSA. Culture-based detection of MRSA requires isolation of pure colonies followed by either oxacillin or cefoxitin susceptibility testing, detection of the mecA gene or detection of the penicillin binding protein (PBP 2a) encoded by the mecA gene. The culture based process takes a minimum of 24 hours with a median time to result closer to 48 hours in order to identify MRSA. With the ability for MRSA infections to spread rapidly, providing nasal carriage results on the same day that the specimen was collected represents an advantage for infection prevention programs.

Active surveillance using molecular tests for rapid detection of MRSA is a proven strategy to reduce transmission in healthcare settings and prevent infection in vulnerable patients. Inaccurate detection can lead to uncontrolled transmission of MRSA and inappropriate use of healthcare resources. With other commercial assays, up to 17.9% of positive MRSA test results are incorrect because the mecA gene is absent, commonly called "dropout mutants". These false positive results can lead to unnecessary and costly isolation and treatment of patients. Strains of MRSA with the newly discovered mecC gene account for 3-4% of all new MRSA cases but cannot be detected by assays that do not detect the mecC gene. Lack of detection of the mecC gene could lead to false negative results which may contribute to uncontrolled transmission of undetected strains of MRSA. Assay design is critical to accurate detection of MRSA and ensure that appropriate infection control interventions are applied. The BD MAX MRSA XT assay uses an extended combination of primers and probes to detect new strains of MRSA, including strains with mecA or mecC gene, and decrease false positives due to mecA or mecC dropouts.

_{Source: BD MAX^TM, MRSA XT Package Insert. REF #443461 06/2016}