Infectious Disease Epidemiology Program

Methicillin-resistant Staphylococcus Aureus (MRSA)

Methicillin-resistant Staphylococcus Aureus (MRSA) is a type of staph bacteria that is resistant to certain antibiotics called beta-lactams.  These antibiotics include methicillin and other more common antibiotics such as oxacillin, penicillin, and amoxicillin.  In the community, most MRSA infections are skin infections and these are considered non-invasive.  When a person has MRSA bacteria, but it does not cause illness it is called "colonization."  While 25 – 30% of people are colonized in the nose with staph, less than 2% of people are colonized with MRSA (Gorwitz RJ et al.  Journal of Infectious Diseases, 2008:"197:1226-34.).

Severe or potentially life-threatening MRSA infections occur most frequently among patients in healthcare settings with an invasive MRSA infection. Patients in healthcare facilities may have weakened immune systems, undergo procedures (such as surgery) or have catheters inserted into the skin. These conditions make it easier for MRSA to get into the body and infect sterile sites, such as blood, CSF, or synovial fluid.

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