What is methicillin-resistant Staphylococcus aureus (MRSA)?

Methicillin-resistant Staphylococcus aureus (MRSA) is a type of staphylococcus or "staph" bacterium that is resistant to many antibiotics. Staph bacteria, like other kinds of bacteria, normally live on your skin and in your nose, usually without causing problems. But if these bacteria become resistant to antibiotics, they can cause serious infections, especially in people who are ill or weak. MRSA is different from other types of staph because it cannot be treated with certain antibiotics such as methicillin.

MRSA infections are more difficult to treat than ordinary staph infections. This is because the strains of staph known as MRSA do not respond well to many common antibiotics used to kill bacteria. When methicillin and other antibiotics do not kill the bacteria causing an infection, it becomes harder to get rid of the infection.

MRSA bacteria are more likely to develop when antibiotics are used too often or are not used correctly. Given enough time, bacteria can change so that these antibiotics no longer work well.

How is MRSA spread?

MRSA, like all staph bacteria, can be spread from one person to another through casual contact or through contaminated objects. It is commonly spread from the hands of someone who has MRSA. This could be anyone in a health care setting or in the community. MRSA is usually not spread through the air like the common cold or flu virus, unless a person has MRSA pneumonia and is coughing.

MRSA that is acquired in a hospital or health care setting is called healthcare-associated methicillin-resistant Staphylococcus aureus (HA-MRSA). In most cases, a person who is already sick or who has a weakened immune system becomes infected with HA-MRSA. These infections can occur in wounds or skin, burns, and IV or other sites where tubes enter the body, as well as in the eyes, bones, heart, or blood.

In the past, MRSA infected people who had chronic illnesses. But now MRSA has become more common in healthy people. These infections can occur among people who have scratches, cuts, or wounds and who have close contact with one another, such as members of sports teams. This type of MRSA is called community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA).