Staphylococcus aureus and MRSA

What is Staphylococcus aureus?
Staphylococcus aureus (pronounced staf-ill-o-kok-us or-ee-us), or “Staph aureus” for short, is a common bacteria (or “germ”) that can cause a wide variety of infections in people, both in community and hospital settings.

Where is Staph aureus found?
Staph aureus is commonly carried on the skin and in the nose of humans, where it mostly causes no harm (this is termed as carriage or colonisation by the bacteria). It has been documented that 30% of people continuously carry Staph aureus in their noses, while many other people carry the bacteria, without any ill effects, from time to time.

Colonisation with Staph aureus is NOT the same as infection with Staph aureus:

• Colonisation is when someone carries a bacteria around with them without any ill effects
• Infection is when a bacteria manages to get through the skin (for example through a cut) or into other parts of the body where it can multiply and cause a person to become ill. 

How is Staph aureus spread?
Staph aureus is mainly spread by direct person-to-person contact (e.g. on unwashed hands) or through indirect contact by touching objects that have been contaminated with the bacteria. Staph aureus is only rarely transmitted through the air. 

What infections are associated with Staph aureus?
Staph aureus infections can be localised (confined to one part of the body) or generalised (spread to many parts of the body). Most Staph aureus infections are relatively minor and do not cause a person to become very ill (for example, a boil or an infected cut in the skin). Staph aureus can cause more severe infections that may require treatment in hospital, but these are relatively rare.

Examples of infections caused by Staph aureus include:

• Infected skin wounds or cuts
• Boils
• Impetigo
• Cellulitis (a type of skin infection)
• Urinary tract infection (“cystitis”)
• Sinus infections
• Pneumonia
• Bone and joint infections
• Bacteraemia (also know as bloodstream infection or “blood poisoning”)

Some types of Staph aureus can produce toxins (a chemical produced by bacteria that can cause illness). The toxins can cause:

• Food-poisoning
• Staphylococcal scalded skin syndrome (also known as Ritter’s disease, Lyell’s syndrome or toxic epidermal necrosis)
• Toxic shock syndrome

Please note: Staph aureus is not exclusively the cause of all of the above infections/diseases.  Many of the above infections can be caused by other bacteria.

How are infections with Staph aureus treated?
Most strains of Staph aureus are treated with penicillin-type antibiotics, such as flucloxacillin, cloxacillin and dicloxacillin (methicillin also belongs to this group). Alternative antibiotics, such as erythromycin, may be used in persons who are allergic to penicillin. 

What is MRSA?
MRSA stands for Meticillin-Resistant Staphylococcus aureus. MRSA is a subgroup of Staph aureus that is resistant to a range of antibiotics, including penicillin antibiotics. MRSA first appeared in 1961 soon after the introduction of the antibiotic meticillin (an antibiotic that is no longer in use). Since then MRSA has spread widely in many countries and has been particularly associated with hospitals and other healthcare facilities.

What is MSSA?
MSSA stands for Meticillin-Sensitive Staphylococcus aureus and refers to all of the antibiotic-sensitive strains of Staph aureus. In other words, MSSA is the common type of Staph aureus that causes most Staph aureus infections and can be treated with penicillin-type antibiotics. 

Can MRSA be treated with antibiotics?
By definition, MRSA are resistant to all “beta-lactam” antibiotics (for example, penicillins and cephalosporins). Most strains of MRSA are also resistant to many other types of antibiotics.

Most MRSA strains can be treated with antibiotics such as vancomycin and teicoplanin, and these are usually the drugs of choice for treating serious MRSA infections.

Recently some strains of MRSA have developed resistance to vancomycin and teicoplanin, though such strains have not been seen in Ireland. The concern is that if we overuse these antibiotics these strains will become more common and will make MRSA even more difficult to treat.

What is the difference between different types or strains of MRSA?
There are different types or strains of MRSA. Some types or strains of MRSA are termed sporadic as they are encountered only sporadically and are rarely a cause of infection. Other strains of MRSA have a propensity to spread in the hospital environment thus becoming endemic. Spread between hospitals is a major problem with such strains, and they are therefore often referred to as epidemic MRSA (EMRSA). EMRSA strains are often widespread throughout a country and similar strains may be found in other countries/continents. There is plenty of evidence for international transfer of EMRSA strains. The predominant strain of EMRSA in Ireland associated with bloodstream infections appears to be related to similar strains in the UK, Germany, Scandinavia and Australia.

Are MRSA infections more serious than MSSA infections?
In general MRSA is no more likely to cause an infection than MSSA. Both MRSA and MSSA can cause localised or minor infections and, occasionally, generalised or severe infections. Because MRSA is resistant to a wide range of antibiotics this makes antibiotic treatment more difficult. As a result people with severe infections caused by MRSA tend to remain ill for longer. For very severe, life-threatening, infections the risk of death is about two times higher with MRSA than with MSSA.

Who is most at risk of getting an MRSA infection?
In general MRSA infections tend to occur in older hospital patients and those with the most severe underlying illnesses. The following are considered to be important risk factors for invasive MRSA infection:

• Age (older age groups are more prone)
• Gender (males are twice-more at risk than females)
• Prolonged hospital stay
• Patients in intensive care, surgical and burns units
• Patients with diabetes and other chronic conditions
• Patients treated with broad-spectrum antibiotics  

How do I know I have MRSA?
The MRSA bacteria will have been identified from a swab or other specimen taken from you, typically from the nose, groin or any surgical wound site. If you were MRSA-positive on a previous stay in hospital, it is also possible that you are still MRSA-positive. 

What happens if a patient has MRSA?
Most patients who have MRSA are colonised and only about one in five will develop an infection. Once MRSA has been detected, it is important that certain measures are taken to de-colonise (remove the MRSA bacteria from the skin or other sites) the patient and to limit any further spread of bacteria.

Patients with MRSA 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 should be changed for each patient encounter.

Good hygiene is essential for the control of MRSA 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 MRSA or not). Soap and warm water or alcohol rubs are provided for this purpose. MRSA is NOT a problem for people visiting sick relatives or friends.

In order to remove the MRSA bacteria from the skin or nose of affected patients, an antibiotic cream may be applied topically.

If a patient has an infection due to MRSA, 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 MRSA. Usually three consecutively clear sets of swabs are required before a patient is considered to be free from MRSA. 

What is the best way to control the spread of MRSA?
The most important infection control measure and the easiest way to help prevent MRSA from spreading within the hospital (and by extension in the community) is to foster strict adherence to hand-washing policies and other hygienic practices for all staff and visitors. 

How common is Staph aureus/MRSA infection in Ireland?
Staph aureus is one of the commonest causes of bloodstream infection (or bacteraemia). At its peak, there were 1,424 reports of Staph aureus bloodstream infection from all acute hospitals (covering 100% of the Irish population) in 2005. Of these, 592 (or 41.6%) were MRSA. Since then, the numbers of Staph aureus and MRSA bloodstream infections have fallen considerably. In 2012, there were 1,060 reports of Staph aureus bloodstream infection, representing a decrease of approximately 26% compared to the data for 2005. Of these, 242 (22.8%) were MRSA, a decrease of approximately 59%.

Latest Irish data on Staph aureus/MRSA bloodstream infections

What is the situation in other European countries?
MRSA is a global concern and not just an Irish problem. In Europe, the highest rates (proportions) of MRSA bacteraemia are observed in Southern Europe (with >40% MRSA in Romania, Portugal, Malta and Greece in 2012). The lowest rates are observed in the Netherlands and Nordic countries (consistently <5%). Between 2009 and 2012, significant decreasing trends in MRSA were observed in seven EARS-Net countries, including Ireland.

For the latest European data and further information, visit the website (with annual reports and interactive database) of the European Antimicrobial Resistance Surveillance Network (EARS-Net) at: http://www.ecdc.europa.eu/en/activities/surveillance/EARS-Net/Pages/index.aspx

What are Irish hospitals doing to address the problem with MRSA?
All Irish hospitals have infection control committees and local guidelines in place for dealing with MRSA and other similar bacteria. National guidelines on hand hygiene in healthcare settings have been produced and the current national guidelines on controlling MRSA are also being updated, to reflect best international practice.

A Strategy for the control of Antimicrobial Resistance in Ireland (SARI) was launched in 2001 and many local, regional and national initiatives are being developed to help tackle this important problem in Ireland.

Last updated: 29 January 2014