M.R.S.A. How much do we know about this methicillin resistant 'superbug'?

Aform of bacteria called Staphylococcus aureus (Staph aureus), M.R.S.A has become resistant to standard antibiotics – including methicillin (i.e. Methicillin Resistant Staphylococcus Aureus). It is often referred to as a 'superbug' due to its ability to resist treatment.

It is estimated that one in three healthy people carry Staphyloccocus aureus bacteria on their skin, in their noses or in the back of their throats. Studies have looked at how many healthy people who are not in hospital carry M.R.S.A - one study estimates about one in 100 people. This is about the same as US studies estimate. People carrying the bacteria are said to be colonised, but not infected: the bacteria are simply "hitching a lift" on the surface of the body and have not entered the body. While they are being carried, all Staph aureus bacteria, including M.R.S.A, are not harmful to a healthy person.

Therefore, most people are rarely aware that they are carrying the bacteria. Infection occurs if the bacteria enter the body through a cut, graze or any other break in the skin (e.g. surgical incision).The severity of the infection depends where in the body the infection has spread to.

So how did M.R.S.A become resistant to these antibiotics?
Whenever bacteria encounter an antibiotic (such as methicillin) some of them may be able to survive it. The surviving methicillinresistant bacteria can then multiply, potentially producing bacteria with even better resistance. The chances of resistant bacteria developing have been increased by:

• failure to finish full courses of antibiotics, allowing bacteria with some resistance to survive and multiply
• overuse of antibiotics, meaning that bacteria encounter and survive a wide range of antibiotics

How is it contracted and spread?
M.R.S.A is usually passed on by direct or indirect physical contact. Most cases are passed on through hand contact. Patients in hospital are particularly vulnerable as the bacteria are easily spread from person to person. One of the reasons hospital patients are most at risk of M.R.S.A is that they often have an entry point for the infection to get into the body such as surgical wounds, a catheter or intravenous line.

As with ordinary strains of Staph aureus, some patients carry M.R.S.A on their skin or nose without it causing any harm. These patients can infect themselves when M.R.S.A spreads from an initial site of colonisation (e.g. from nose to a wound). The resulting infection is described as 'endogenous'.

Infected patients can spread the bacteria to other patients and hospital staff who may then become colonised (perhaps only briefly) and spread the bacteria to other patients they have contact with. These patients may in turn become colonised or infected. M.R.S.A can survive on inanimate objects or surfaces such as linen, sinks, floors and cleaning equipment. Infection can also be spread in this way.

Some strains of M.R.S.A may also spread between hospitals when colonised patients or staff move from one hospital to another. There have also been a small number of cases of communityacquired M.R.S.A, which have been spread among people who have not been in contact with hospitals. How do we prevent the spread of M.R.S.A?

The M.R.S.A bacteria are identified from a swab or other specimen taken from the patient, typically from the nose, groin or any surgical wound site. If a person was M.R.S.A-positive on a previous stay in hospital, it is possible that they are still M.R.S.A-positive. Measures to prevent the spread of organisms from one person to another are called infection control. The spread of M.R.S.A can be greatly reduced by isolating the affected individual.

Once M.R.S.A has been detected, it is important that certain measures are taken to de-colonise (remove the M.R.S.A bacteria from the skin or other sites) the patient and to limit any further spread of bacteria. Patients with M.R.S.A are usually moved to a single room or dedicated isolation ward to prevent the spread of the organism to other patients and staff. Staff will wear gloves and gowns to help prevent contamination of their skin and clothes (and thus further spread of the bacteria to other patients and staff members). Gloves and gowns are changed for each patient encounter.

The main factor in the spread of M.R.S.A is hand washing. Hand washing can reduce the rate of transmission by up to 33%. Good hygiene is essential for the control of M.R.S.A and other infections. Staff and visitors alike should be careful to wash their hands thoroughly before and after visiting a patient (this is good practice regardless of whether the patient has M.R.S.A or not). Soap and warm water or alcohol rubs are provided for this purpose.

In order to remove the M.R.S.A bacteria from the skin or nose of affected patients, an antibiotic cream may be applied topically. If a patient has an infection due to M.R.S.A, appropriate antibiotic treatment will be started, e.g. with vancomycin, teicoplanin or another appropriate antibiotic.

Swabs will be taken intermittently from sites where the bacteria are typically found (e.g. nose, throat, armpit, wrist, groin, any wounds). These are tested for the presence of M.R.S.A. Usually three consecutively clear sets of swabs are required before a patient is considered to be free from M.R.S.A.

Where can I get further information?

• Information on the current levels of M.R.S.A, and other infections, in Ireland can be found in the EARSS section of the Health Protection Surveillance Centre (HPSC) website: www.hpsc.ie
• The 1999 North/South study of M.R.S.A in Ireland is available from the Department of Health and Children's website: www.dohc.ie
• The UK Health Protection Agency has background information on M.R.S.A in the "Topics A-Z" section of its website: www.hpa.org.uk
• The US Centres for Disease Control (CDC) website has information on M.R.S.A (look under "A-Z Index"): www.cdc.gov