Staphylococcus aureus (commonly called Staph) is a common bug or bacteria that is found on the skin and in the nostrils of about 1 in every 3 people. The bacteria usually live harmlessly without causing you to become ill and you don't require treatment for them. However, if these bacteria get into a wound or open cut, they can cause infections that range from boils on your skin to more severe infections of your bones, lungs and blood. These need treatment with antibiotics.
Methicillin-resistant Staphylococcus aureus (MRSA) are a group of Staph bacteria that have become resistant to commonly used penicillin-like antibiotics. This means that infections caused by MRSA bacteria require different antibiotics and can be more difficult to treat. Read more about antibiotic resistance.
Having MRSA is of particular concern in hospitals where there is a greater chance of bugs (bacteria) entering your body because of openings to your skin caused by operations, procedures and drips (intravenous lines). This puts you at risk of developing severe infections.