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. These tests detect the presence of MRSA in a patient's sample.
Staphylococcus aureus frequently colonizes the human skin and is present in the nose of about 25-30% of U.S. adults. It does not usually cause harm 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, 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 Wound Infections and Methicillin Resistant Staphylococcus aureus.]
MRSA can be spread in health care 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, MRSA is usually spread by sharing personal care items, participating in contact sports, or living or working in a place where there is close contact with others – anything that allows for skin-to-skin contact.
Most hospitals have instituted measures to attempt to eradicate MRSA and to control the spread of MRSA from person to person. Nine U.S. states mandate MRSA screening of all patients in the intensive care unit (ICU) of a hospital. 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. A study comparing prevention strategies for bloodstream infections found, however, that decolonizing ICU patients who are MRSA-positive based on screening tests was not as effective at reducing these infections as decolonizing all patients admitted to the ICU. As a result, hospital policies may change in the future and less MRSA screening may be performed in these settings. However, the state regulatory requirement for MRSA screening would have to be changed before hospitals in those states with the mandate could adopt a "no MRSA screening" policy.
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.