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Methicillin-Resistant Staphylococcus aureus (MRSA)

Methicillin-Resistant Staphylococcus aureus (MRSA)


Staphylococcus aureus, often referred to as "staph," is a very common bacteria. Approximately 25-30% of healthy people carry this organism on their skin or in their nose.

Sometimes, staph causes an infection. Staph bacteria are the most common causes of skin infections in the United States. Infections caused by staph can appear as pimples, boils, and abscesses - staph infections may also be mistaken for bites from insects or spiders. Sometimes, staph can cause more severe infections inside the body. These are called invasive infections and include pneumonia, bone infections, and toxic shock syndrome. But the vast majority of staph infections are not invasive, and involve only the skin.


Methicillin-resistant Staphylococcus aureus (MRSA) is a type of staph that is resistant to certain antibiotics. These antibiotics include methicillin and other [narrow-spectrum B-lactamase-resistant penicillin antibiotics] such as cloxacillin, dicloxacillin, oxacillin, and nafcillin, as well as a closely related class of drugs known as cephalosporins (e.g., cephalexin). Overuse of antibiotics and the use of more powerful drugs than necessary for less serious infections may be some of the causes of the development of MRSA.

Approximately 1-2% of people carry MRSA on their skin or in their nose. Infections caused by MRSA, for the most part, are not different from any other staph infection, although some strains of MRSA may be more aggressive than regular staph.

The diagnosis of a MRSA infection requires laboratory testing. Laboratory testing can also be important since MRSA's antibiotic resistance may make it more difficult to manage; testing can guide treatment.

The diagnosis of a MRSA infection requires laboratory testing. Your doctor might recommend laboratory testing of a wound that looks infected and is not healing properly in order to confirm whether it is caused by MRSA and to determine which antibiotics might be useful in treating it.

Transmission of Staph

The main way that staph (including MRSA) is spread is from one person to another on hands. The bacteria may also be spread by contact with contaminated items (e.g., razors, sports equipment, towels) or environmental surfaces (e.g., athletic benches or mats). Factors contributing to transmission include close skin-to-skin contact, openings in the skin such as cuts and abrasions, the presence of contaminated items, crowded living conditions, and poor hygiene.

Staph can cause mild to serious infections, and they are all spread the same way. Serious infections are not easier to spread than mild ones. MRSA is not easier to spread than other staph infections.

Settings Where MRSA Occurs

MRSA has traditionally been seen as associated with healthcare settings, both in hospitals and in non-hospital healthcare facilities (such as dialysis centers). Infections in these settings are referred to as healthcare-associated MRSA, or HA-MRSA. However, MRSA infections are increasingly occurring in people who have not recently been hospitalized or had a medical procedure. These infections are known as community-associated MRSA (CA-MRSA). Examples of groups that have experienced outbreaks of CA-MRSA include persons living in correctional facilities or participating on competitive sports teams.

A person can carry MRSA, without symptoms, for a long time before getting sick. This can make it extremely difficult to determine where a person might have acquired his or her MRSA infection. The place of onset of illness may have nothing to do with the place where the bacterium was acquired.

Colonization vs Infection

The distinction between staph (including MRSA) colonization and infection is important.

Colonization = the presence of the bacteria, but no signs of illness or infection. Staph thrives in warm, moist places; common sites of colonization include the nostrils, belly button, underarms, groin, etc.

Infection = clinical signs of illness or inflammation (e.g., localized pain/tenderness, redness, warmth, swelling; pus; fever). These are due to tissue damage caused by invasion by the bacteria. Infection requires treatment - various treatment options exist. Treatment does not always require the use of an antibiotic.

Management and Treatment

No treatment is needed for colonization. Most people do not know they are colonized because the bacteria are present but not causing any symptoms. Everyone should practice good hand hygiene and proper wound care to help ensure that bacteria do not enter the body through breaks in the skin and potentially cause infections.

Most minor skin infections (such as pimples and boils) can be treated with appropriate wound care at home through proper cleaning of wounds and covering them with bandages. Additional actions are needed for wounds that are not healing properly or that are draining (e.g., see a physician for possible drainage of pus with warm compresses or incision and sometimes, antibiotics). However, more serious infections (such as surgical wound infections, bloodstream infections, pneumonia) need to be treated aggressively. This may require hospitalization and/or the use of intravenous (IV) antibiotics. Laboratory testing of the organism is often necessary to make sure the right antibiotic is being used.

Frequent and thorough hand washing, not sharing personal items, and proper wound care are the key ways to reduce the risk of spreading the organism to others.

Basic Steps for Prevention

Reduce the risk of spreading staph, including MRSA to others by following these steps:

  • Cover wounds. Pus from infected wounds can contain staph. Cover wounds that are draining or have pus with clean, dry bandages. Follow your healthcare provider's instructions on proper care of the wound. Bandages or tape can be discarded with the regular trash.

  • Keep hands clean. Wash bare hands frequently with soap and warm water, especially after changing a bandage or touching an infected wound (even if gloves are worn). Alcohol-based hand sanitizers may be used if hands are not visibly soiled.

  • Do not share personal items. Avoid sharing personal items such as towels, washcloths, razors, clothing, or uniforms. Wash soiled sheets, towels, and clothes with warm/hot water and laundry detergent. Drying clothes in a hot dryer, rather than air-drying, also helps kill bacteria in clothes.

  • Talk to your doctor. Tell any healthcare providers who treat you if you have had a MRSA infection.

Learn More About MRSA

Last Updated: 01-10-2013

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