What Is MRSA? (Methicillin Resistant Staphylococcus aureus)
Source: State of Wisconsin Department of Health and Family Services
October 22, 2007
Staphylococcus aureus (S. aureus) is a bacterium normally found in the nose or on the skin of about 20 to 30 percent of people in the United States. Infections caused by S. aureus include mild to severe skin and soft tissue infections, blood stream infections, pneumonia, and toxic shock syndrome.
Health Care Associated MRSA
Methicillin resistant S. aureus (MRSA) is a form of S. aureus that is resistant to certain antibiotics. MRSA first appeared in the 1960s in hospitals in this country. It is usually acquired in the hospital or long-term care setting, occurs more often in older persons, those who have been on antibiotics, have had surgery, or have an indwelling device such as a ventilator, urinary catheter, or intravenous catheter. This form of MRSA is referred to as health care associated, or HA MRSA. About 15 percent of the United States population carries HA MRSA.
According to data collected by the CDC Active Bacterial Core Surveillance Program, approximately 90,000 cases of invasive MRSA occur each year in the United States, and about 20 percent of cases result in death. Applying this estimate to the Wisconsin population, roughly 1,700 cases of invasive MRSA infections occur each year in the state, resulting in approximately 340 deaths annually. By comparison, approximately 100 people die of AIDS in Wisconsin each year.
Community Associated MRSA
Beginning in the 1990s, the number of MRSA infections diagnosed in persons with no typical health care associated risk factors began increasing. These community associated (CA) MRSA strains differ from HA MRSA strains found in hospitals and nursing homes in the following ways:
- CA MRSA typically affects younger people (children under age 2 are especially susceptible) while HA MRSA infections are more often found in older persons.
- Generally, most CA MRSA infections are mild skin and soft tissue infections while most HA MRSA infections are more serious and invasive (blood stream infections, surgical site infections, pneumonia).
- CA MRSA strains are more susceptible to antibiotics than HA MRSA strains. There are more choices for treatment of CA MRSA infections than for HA MRSA infections.
- CA MRSA strains spread more rapidly in the community than do HA MRSA strains. HA MRSA is confined mostly to health care settings.
- CA MRSA strains appear to be more virulent than susceptible S. aureus strains. HA MRSA strains are usually not more virulent than susceptible strains of S. aureus. Increased mortality from HA MRSA is usually due to delays in effective treatment and because the antibiotics available to treat HA MRSA are less effective than those used to treat antibiotic-sensitive strains.
- CA MRSA strains cause about 20 percent of all MRSA infections; HA MRSA strains cause about 80 percent of all MRSA infections.
Although only about 1 percent of the U.S. population carries CA MRSA, it is now the leading cause of pus-producing skin and soft tissue infections among adults.
For more information, see Wisconsin Division of Public Health Guidelines for CA MRSA and patient education pamphlet at http://dhfs.wisconsin.gov/communicable/resources/HlthProvider.htm
How is MRSA spread?
CA MRSA is spread primarily by direct person-to-person contact but can also be transmitted indirectly through contaminated objects, surfaces, and equipment. The bacterium may enter through tears or cuts in the skin. Outbreaks of CA MRSA have occurred among members of contact sports teams and in prison settings.
Although CA MRSA can cause serious, life-threatening illness, and in some cases death, these outcomes are relatively uncommon, and the vast majority of CA MRSA infections are skin and soft tissue infections from which people recover. CA MRSA strains are resistant to some antibiotics but remains susceptible to many antibiotics which can be used to successfully treat CA MRSA infections.
How can MRSA be prevented?
There are steps everyone can take to help reduce the chances of acquiring a CA MRSA infection:
- Keep skin clean—wash hands often with soap and water or use alcohol gel, and shower or bathe routinely, especially after athletic activities.
- Keep skin healthy—wear protective clothing and gear during contact sports activities, wear gloves to protect skin on hands when gardening, use lotions to keep skin moist and sun screen to prevent blisters due to sunburn.
- Do not share towels, razors, bars of soap, water bottles, or other personal items.
- Cover cuts, scrapes, and tears in the skin with a protective bandage or dressing.
- Do not go to school, work, day care, or participate in sports activities if wound drainage cannot be covered and contained with a bandage or clean, dry dressing. Once drainage can be contained, it is permissible to resume activities and return to work or school.
- Clean and disinfect environmental surfaces and items contaminated with wound drainage. Practice routine cleaning and disinfection of sports equipment, wrestling mats, locker rooms, shower rooms, and weight rooms.
