Staphylococcus aureus is a bacterium (germ). It is often just called 'S.aureus' or 'staph'. S. aureus bacteria are often found on the skin and in the nose of healthy people. In fact, about 3 in 10 people have S. aureus bacteria living on (colonising) their skin. These people are called S.aureus 'carriers'. In healthy people who are carriers, S.aureus is usually harmless.

However, the bacteria sometimes invade the skin to cause infection. This is more likely if you have a cut or graze which can allow bacteria to get under the surface of the skin. It is the cause of skin infections such as boils, pimples, impetigo, skin abscesses, and is a common cause of wound infections.

MRSA stands for Methicillin-Resistant Staphylococcus aureus. MRSA strains are very similar to any other strain of S.aureus. That is, some healthy people are carriers, and some people develop the types of infections described above. The difference is that, most S.aureus infections can be treated with commonly used antibiotics. In recent years some strains of S.aureus have become resistant to some antibiotics. 'Resistance' means that it is not killed by the antibiotic. MRSA strains are not only resistant to the antibiotic called methicillin, but also to many other types of antibiotics.

MRSA strains of bacteria are no more aggressive or infectious than other strains of S.aureus. However, infections are much more difficult to treat because many antibiotics do not work. Therefore, infections tend to become more severe than they may otherwise have been if the cause of the infection is not diagnosed early, and antibiotics that do not work are given at first.

MRSA occurs most commonly in people who are already ill. People who are more prone to it are those who are very ill, or have wounds or open sores such as bed-sores or burns. The wounds or sores may become infected with MRSA and the infection is then difficult to treat. Infections which start in the skin may spread to cause more serious infections. MRSA can also cause infections in people outside hospital, but much less commonly than in hospitalised people.

If an infection with S.aureus is suspected then, depending on the type of infection, a sample of blood, urine, body fluid, or a swab of a wound can be sent to the 'lab' for testing. If S.aureus is detected, further tests are done to see which antibiotics will kill the bacteria. MRSA strains can be identified by seeing which antibiotics kill the bacteria found on testing. Healthy people suspected of being carriers of MRSA can have a swab or the nose or skin taken and tested.

S.aureus bacteria (including MRSA strains) spread from person to person usually by direct skin-to-skin contact. Spread may also occur by touching sheets, towels, clothes, dressings, etc, which have been used by someone who has MRSA. However, as mentioned, S.aureus (including MRSA strains) will not normally cause infection if you are well. The bacteria may get onto your skin, but do no harm. So, for example, people who visit patients with MRSA, or doctors and nurses who treat people with MRSA, are not likely to develop an MRSA infection. But, they may become 'contaminated' with the bacteria and may pass it on to someone who is ill, or who has a wound, who then may develop infection.

MRSA infections are usually treated with antibiotics. However, the choice of antibiotic is limited as many antibiotics will not work. Many MRSA infections can only be treated with antibiotics that need to be given directly into a vein. The course of treatment can be for several weeks.

People who are carriers of MRSA but who are healthy do not need any treatment. However, in some cases it may be advised to try and clear the bacteria from the skin by washing with antiseptic lotions, and using antiseptic shampoos, and using an antibiotic cream to place in the nose. These measures may reduce the risk of developing an infection, or spreading the bacterium to others (particularly to ill people who may develop an infection).

The number of MRSA infections in hospital can be kept down if all hospital staff adhere to good hygiene measures. This has been a key element of our work. The most important is to wash hands before and after contact with each patient, and before doing any any procedure. This simple measure reduces the chance of passing on bacteria from patient to patient. We also encourage our visitors to take these steps and use the alcohol hand gels we provide on wards and entrances.

Other measures are used in our hospitals to reduce the spread of infection. For example, cleaning of bedding, regular cleaning of wards and screening of patients before they come in for surgery. We also have a specialist infection ward so that patients with an MRSA infection can be cared for by our specialist teams and get the care they need until the infection has cleared and reduce the risk of passing infection to other patients.

We also screen patients in advance of their surgery (or on admission if you are an emergency patient) so that we can identify if you are naturally carrying the bacteria. By identifying this we can stop it causing any problems.