Methicillin-resistiant staphylococcus aureus (MRSA) is a particular strain of the common staphylococcus aureus bacterium which can live in noses and on human skin.
About one in three people has the bacterium in his or her nose, which may manifest itself in a stye in the eye or a boil - but can develop into a serious infection in vulnerable patients.
The MRSA strain is resistant to penicillins and other antibiotics. It was first discovered in Britain more than 45 years ago, and is now rife in hospitals and other healthcare settings. Infections caused by MRSA can be confined to one part of the body or can spread.
Transmission is through physical contact, or indirectly through bedding and equipment in health care institutions.
Those at risk include older people, long-term patients or residents in institutions, diabetics, patients in ICU or who have had surgery, victims of burns, immuno-compromised patients and patients treated with many antibiotics.
Swabbing and laboratory testing is the only reliable method of detection. Early detection allows for prompt treatment, and for isolation of patients if necessary.