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The Test Sample
What is being tested?
Methicillin-resistant Staphylococcus aureus (MRSA) are strains of Staphylococcus aureus, or "staph," bacteria that are resistant to the antibiotic methicillin as well as to related beta-lactam antibiotics, such as oxacillin, penicillin, amoxicillin, and cephalosporins, that are used to treat ordinary staph infections. MRSA testing detects the presence of MRSA in a patient's sample. Photo source: NIAID, Frank Deleo
Staphylococcus aureus frequently colonizes the human skin and is present in the nose of about a third of U.S. adults. It does not usually cause illness or symptoms. However, if there is a break in someone's skin from a wound or surgery, or if someone's immune system is weakened, then colonizing S. aureus can cause an infection.
Widespread use of antibiotics over the past several decades have led to the development of antibiotic-resistant strains of S. aureus. Infection with these strains can cause skin infections and potentially more severe, life-threatening infections such as pneumonia, bloodstream infections (septicemia), or infections at a surgical site. However, according to the Centers for Disease Control and Prevention (CDC), less than 2% of the population carries the type of staph bacteria known as MRSA. [For more on this, see the article Staph Infections and Methicillin-Resistant Staphylococcus aureus.]
MRSA can be spread in healthcare settings and in the community. Contaminated hands, medical equipment, and surfaces in places such as hospitals, clinics, or nursing homes allow the spread of MRSA from colonized or infected patients. In the community, anything that allows for skin-to-skin contact can spread MRSA. This includes sharing personal care items, participating in contact sports, or living or working in close contact with others.
Most hospitals have instituted measures to attempt to eradicate MRSA and to control the spread of MRSA from person to person. Those who test positive for MRSA may be isolated to prevent the spread to others and/or decolonized with a nasal antibiotic ointment and daily cleansing with special antimicrobial wipes. However, exactly how to implement MRSA screening and control in healthcare settings remains somewhat controversial. For example, a 2014 study comparing prevention strategies for bloodstream infections found that treating to eliminate MRSA from intensive care unit (ICU) patients who screen positive was not as effective at reducing these infections as treating all patients admitted to the ICU. This treatment may involve administering antibiotics within the nose and cleansing patients with special antimicrobial wipes. As a result, hospital policies may change in the future and less MRSA screening may be performed in these settings.
How is the sample collected for testing?
A nasal swab is collected by rotating a swab inside each nostril. Occasionally, a swab of a wound infection site or skin lesion is collected.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.