MRSA stands for meticillin-resistant Staphylococcus aureus, which is a common skin bacterium that is resistant to a range of antibiotics.
'Meticillin-resistant' means the bacteria are unaffected by meticillin, a type of antibiotic that used to be able to kill them.
An MRSA infection means the bacteria have got into the body through a break in the skin (see below) and multiplied, causing symptoms.
The symptoms of MRSA infection vary depending on which part of the body is infected, but there is often redness and swelling at the site of infection.
Colonisation
About one in three of us carries the Staphylococcus aureus (SA) bacteria in our nose or on the surface of our skin (especially in folds like the armpit or groin) without developing an infection. This is known as being colonised by the bacteria.
In hospitals, the proportion of people colonised by MRSA is higher because of more contact with infected cases (see below).
People can carry MRSA for a few hours or days or sometimes for weeks or months. They are unaware they are carriers because the bacteria do not harm them or cause symptoms, unlike people who are infected with MRSA.
How infection happens
If SA bacteria get into the body through a break in the skin, they can cause infections such as boils, an abscess or impetigo. If they get into the bloodstream they can cause more serious infections, such as blood poisoning (see Symptoms page).
Who is most at risk
MRSA will not normally infect a healthy person. Although it is possible for people outside hospital to become infected, MRSA infections are most common in people who are already in hospital. This is because:
- they often have an entry point for the bacteria to get into their body, such as a surgical wound or a catheter,
- they tend to be older, sicker and weaker than the general population, which makes them more vulnerable to infection, and
- they are surrounded by a large number of other patients and staff, so the bacteria can spread easily (through direct contact with other patients or staff, or via contaminated surfaces).
For more information, see the list of at-risk groups.
Screening for MRSA
All NHS patients going into hospital for a relevant planned procedure are screened for MRSA beforehand. This helps the NHS reduce the chance of patients getting an MRSA infection or passing MRSA on to another patient. For more information, see Screening.
Treatment
Bacterial infections are treated with antibiotics. However, MRSA bacteria are resistant to meticillin (a type of penicillin antibiotic), and usually to some of the other antibiotics that are normally used to treat SA infections. Therefore MRSA infections are more difficult to treat than other bacterial infections.
See the box, above left, on how bacteria such as MRSA have become resistant to antibiotics.
Antibiotics can still be used to treat MRSA, but you may need a much higher dose over a much longer period, or treatment with an antibiotic to which the bacteria is not resistant (see Treatment).
Healthcare staff, patients and hospital visitors can take simple hygiene measures, such as regular hand washing, to help prevent the spread of MRSA and stop infection (see Prevention).
