Methicillin-resistant Staphylococcus aureus (MRSA) infection
Written by , clinical scientist
What is MRSA?
MRSA stands for methicillin-resistant Staphylococcus aureus. It is a type of bacterium commonly found on the skin and/or in the noses of healthy people. Although it is usually harmless at these sites, it may occasionally get into the body (eg through breaks in the skin such as abrasions, cuts, wounds, surgical incisions or indwelling catheters) and cause infections. These infections may be mild (eg pimples or boils) or serious (eg infection of the bloodstream, bones or joints).
The treatment of infections due to Staphylococcus aureus was revolutionised in the 1940s by the introduction of the antibiotic penicillin.
Unfortunately, most strains of Staphylococcus aureus are now resistant to penicillin. This is because Staphylococcus aureus has 'learnt' to make a substance called ß-lactamase (pronounced beta-lactamase), that degrades penicillin, destroying its antibacterial activity.
Some related antibiotics, such as methicillin and flucloxacillin, are not affected by ß-lactamase and can still be used to treat many infections due to ß-lactamase-producing strains of Staphylococcus aureus. Unfortunately, however, certain strains of Staphylococcus aureus, known as MRSA, have now also become resistant to treatment with methicillin and flucloxacillin.
Although other types of antibiotics can still be used to treat infections caused by MRSA, these alternative drugs are usually not available in tablet form and must be administered through a drip inserted into a vein.
Who gets infection with MRSA?
MRSA infections most often occur in patients in hospitals and are rarely seen among the general public. As with ordinary strains of Staphylococcus aureus, some patients harbour MRSA on their skin or nose without harm (such patients are said to be 'colonised'), whereas other patients may develop infections.
Some patients are at increased risk of developing infection. They include those with breaks in their skin due to wounds (including those caused by surgery), indwelling catheters or burns, and those with certain types of deficiency in their immune system, such as low numbers of white cells in their blood.
When MRSA spread from an initial site of colonisation to a site where they cause infection in the same patient (eg spread from the colonised nose to a wound), the resulting infection is described as 'endogenous'.
In addition to causing endogenous infections, MRSA can spread between patients, usually by direct or indirect physical contact. For example, hospital staff attending to a colonised or infected patient may become contaminated or colonised with MRSA themselves (perhaps only briefly). They may then spread the bacteria to other patients with whom they subsequently have contact. These patients may in turn become colonised and/or infected. The spread of MRSA (or for that matter other bacteria) between patients is called cross-infection.
Some strains of MRSA that are particularly successful at spreading between patients may also spread between hospitals, presumably when colonised patients or staff move from one hospital to another. These strains are known as epidemic MRSA (or EMRSA for short).
Can the spread of MRSA be controlled?
There are several steps that may be undertaken to minimise the spread of MRSA between patients.
- Hospital staff should wash their hands scrupulously, preferably using antibacterial soap and disposable towels.
- Patients colonised or infected with MRSA may be kept away from other patients by being placed in separate rooms, either alone or with other patients who also have MRSA. Access to such rooms should be restricted to essential personnel.
- Hospital staff should wear gloves and disposable gowns prior to having physical contact with MRSA patients. Before leaving the room, they should discard these safely, and wash their hands.
- Visitors and carers likely to have a lot of physical contact with patients should also wear disposable gloves and gowns. All visitors should wash their hands before leaving the room.
- MRSA can survive on inanimate objects or surfaces such as linen, sinks, floors and even mops used for cleaning. For this reason, areas where MRSA patients are nursed should be thoroughly cleaned using disinfectants.
How is infection or colonisation with MRSA diagnosed?
To diagnose MRSA infection, 'specimens' are taken from the patient, such as a swab of an infected wound or a sample of blood or urine. These are sent to a microbiology laboratory, where bacteria present in the specimen are cultured and identified. This process may take several days. Colonisation with MRSA is detected similarly, using swabs of a person's skin or from the inside of the nose.
How is MRSA treated?
Patients colonised with MRSA
Patients or other individuals simply colonised with MRSA may have a special antibiotic called mupirocin applied onto their skin () or the inside of their nose (). This helps to eliminate the MRSA and reduces the risk of the bacteria spreading either to other sites on the patient's body, where they might cause infection, or to other patients. Some strains of MRSA are, however, resistant to mupirocin.
Individuals colonised with MRSA may also wash their skin and hair with suitable disinfectants, such as chlorhexidine.
Patients infected with MRSA
Patients with infections due to Staphylococcus aureus often need . Infections due to normal strains of Staphylococcus aureus are often treated with , but this is ineffective against MRSA. To make matters worse, MRSA are often also resistant to other types of antibiotics such as and .
Although MRSA are resistant to many drugs, most remain susceptible to the antibiotics and . Infections due to MRSA are therefore often treated with one or other of these drugs. Both must be administered by infusion or injection, and for this reason, they are used for treatment only in hospitalised patients. In addition, injection of vancomycin into muscle is painful and thus not used, while rapid administration into a vein may produce an allergic-type reaction (the so-called 'red man' syndrome). To overcome these problems, vancomycin must be given by slow infusion into a vein. In contrast, teicoplanin may be safely administered by injection into muscle or rapid infusion into a vein.
A very few MRSA resistant to vancomycin and/or teicoplanin have been found and there is concern that they may become more common in the future. Fortunately, new antibiotics that are active against MRSA are under investigation and should hopefully become available for clinical use in the near future.
Recently, one such new drug called has been introduced in the UK. This drug may be given either by intravenous infusion (in severely ill patients) or in tablet form. Clinical trials have so far shown it is useful (either alone or in combination with other antibiotics) for the treatment of pneumonia and skin and soft tissue infections.
MRSAMethicillin-Resistant Staphylococcus Aureus
What is Staphylococcus aureus?
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 (colonizing) their skin. These people are called S. aureus 'carriers'. In healthy people who are carriers, S. aureus is usually harmless.
However, S. aureus 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. S. aureus is the cause of skin infections such as boils, pimples, impetigo, skin abscesses, and is a common cause of wound infections.
In some people, S. aureus can sometimes get into the bloodstream and travel to internal parts of the body to cause more serious infections. For example, blood poisoning (septicaemia), lung infection (pneumonia), bone infection (osteomyelitis), heart valve infection (endocarditis), etc. These serious infections are more likely to occur in people who are already unwell or debilitated, or who have a poor immune system. These infections need to be treated with antibiotics.
What is MRSA?
MRSA stands for methicillin-resistant Staphylococcus aureus. There are various sub-types (strains) of S. aureus and some strains are classed as MRSA. 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.
How serious is an MRSA infection?
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.
Who gets MRSA?
MRSA occurs most commonly in people who are already in hospital. 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. Also, urinary catheters and tubes going into veins or parts of the body ('drips' etc) are sometimes contaminated by MRSA and can lead to urine or blood infection.
MRSA can also cause infections in people outside hospital, but much less commonly than in hospitalized people.
How common is MRSA?
As mentioned, being a carrier of S. aureus and infections with S. aureus are very common. The number of cases due to MRSA strains is not known, but it is becoming a more common problem.
How is MRSA diagnosed?
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.
How is S.aureus and MRSA spread?
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.
What is the treatment of MRSA infections?
MRSA infections are usually treated with antibiotics. (Boils or abscesses caused by MRSA may only need to be drained and may not need antibiotics.) However, the choice of antibiotic is limited as most 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 is often for several weeks. Also, the risk of side-effects with the limited choice of antibiotics is higher than the more 'usual' antibiotics which are used to treat non-MRSA infections.
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).
Can MRSA infections be prevented?
The number of MRSA infections in hospital can be kept down if all hospital staff adhere to good hygiene measures. 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.
Other measures are used in hospitals to reduce the spread of infection. For example, cleaning of bedding, regular cleaning of wards, etc. Patients with an MRSA infection may be kept away from other patients, perhaps in a single bed room or in an isolation unit until the infection has cleared.
Q&A: MRSA 'superbugs'
The number of MRSA deaths doubled in four years between 1999 and 2003, official statistics show.
Ministers have set ambitious targets to tackle the problem - and point to a significant drop in infections during 2004, but the Tories say not enough is being done.
MRSA is resistant to antibiotics
What is MRSA?
Staphylococcus is a family of common bacteria.
Many people naturally carry it in their throats, and it can cause a mild infection in a healthy patient.
MRSA stands for methicillin-resistant Staphylococcus aureus, but is shorthand for any strain of Staphylococcus bacteria which is resistant to one or more conventional antibiotics.
Experts have so far uncovered 17 strains of MRSA, with differing degrees of immunity to the effects of various antibiotics.
Two particular strains, clones 15 and 16, are thought to be more transmissible than the others, and account for 96% of MRSA bloodstream infections in the UK.
At present, these strains are thought to be rare in other countries, but are spreading.
Antibiotics are not completely powerless against MRSA, but patients may require a much higher dose over a much longer period, or the use of an alternative antibiotic to which the bug has less resistance.
What are the symptoms?
MRSA infections can cause a broad range of symptoms depending on the part of the body that is infected. These may include surgical wounds, burns, catheter sites, eye, skin and blood.
Infection often results in redness, swelling and tenderness at the site of infection. Sometimes, people may carry MRSA without having any symptoms.
Why does MRSA exist?
It's all about survival of the fittest - the basic principle of evolution, and bacteria have been around a lot longer than us, so they're pretty good at it.
There are countless different strains of a single type of bacteria, and each has subtle natural genetic mutations which make it different from the other.
In addition, bacterial genes are constantly mutating.
Some strains' genetic makeup will give them a slight advantage when it comes to fighting off antibiotic attack.
So when weaker strains encounter antibiotics, they die, while these naturally resistant strains may prove harder to kill.
This means that next time you encounter Staph, it is more likely to be one which has survived an antibiotic encounter, ie a resistant one.
The advice from doctors who give you antibiotics is always to finish the entire course - advice which many of us ignore.
When you don't finish the course, there's a chance that you'll kill most of the bugs, but not all of them - and the ones that survive are of course likely to be those that are most resistant to antibiotics.
Over time, the bulk of the Staph strains will carry resistance genes, and further mutations may only add to their survival ability.
Strains that manage to carry two or three resistance genes will have extraordinary powers of resistance to antibiotics.
The reason that hospitals seem to be hotbeds for resistant MRSA is because so many different strains are being thrown together with so many doses of antibiotics, vastly accelerating this natural selection process.
Why is it so dangerous?
It is a fact of life in the NHS that patients are at higher than normal risk of picking up a Staph infection on the wards.
This is for two reasons - firstly, that the population in hospitals tends to be older, sicker and weaker than the general population, making them more vulnerable to the infection.
Secondly, conditions in hospitals, which involve a great many people living cheek by jowl, examined by doctors and nurses who have just touched other patients, are the perfect environment for the transmission of all manner of infections.
Staph infections can be dangerous in weakened patients, particularly if they can't be cleared up quickly with antibiotic treatments.
MRSA infections can prove tough to treat because they are resistant to treatment, making them more dangerous than a simple case of Staph.
What is likely to happen in the future?
Doctors are very worried about what the future holds for MRSA.
The number of reports of MRSA infections rises year by year - and the latest evidence suggests that deaths due to MRSA are increasing at a similar rate.
Already, the spectre of a bug resistant to all antibiotics is approaching.
VRSA, or vancomycin resistant Staphylococcus Aureus, has acquired resistance to a drug considered the "last line of defence" when all other antibiotics have failed.
The UK has already seen several cases of GISA, or glycopeptide intermediate Staphylococcus aureus, a kind of "halfway house" between MRSA and VRSA, which has developed a resistance to antibiotics of the vancomycin family.
Although new antibiotics are being developed all the time, pessimistic experts believe it is only a matter of time at current rates until virtually every weapon in the pharmaceutical arsenal is nullified.
Nihilists suggest that there could come a point at which bacteria retake the upper hand, and doctors, as in previous centuries, have no answer to some bacterial infections.
It should be noted, they say, that humans have only had the upper hand over bacteria for a handful of decades - we have no right to expect that situation to last forever.
What can we do about it now?
The government is already trying to at least slow down the apparently relentless march of the bacteria.
One of the main reasons behind their swift evolution into "superbugs" is the overuse of antibiotics, both in human and veterinary medicine.
Until recently, patients visiting their doctor with a viral infection might demand, and be given an antibiotic prescription - despite the fact that antibiotics have no effect on this.
All those patients were doing was strengthening the communities of bacteria in their bodies.
Doctors have now been told to cut antibiotic prescribing.
Hygiene is another tried and tested way of at least protecting the most vulnerable patients from the most dangerous strains.
Handwashing between patients should be a must for doctors and nurses, or they are simply doing more harm than good in their trips around the wards.
Ministers are trying to improve overall standards of hygiene, perhaps by reintroducing the concept of the ward matron, with responsibility for cleanliness.
New patient bedside phones are being introduced that include speed dial buttons to alert staff to the need to deal with a hygiene problem.
Whether a dirty ward rather than a dirty hand is a reservoir for Staphylococcus is a matter of debate.
But MRSA patients are also increasingly being treated in isolation where possible.
In the long run, many experts suggest it may take a breakthrough akin to the discovery of penicillin before humans can regain a temporary upper hand over the bugs again.
What is MRSA?
The organism Staphylococcus aureus is found on many individuals skin and seems to cause no major problems. However if it gets inside the body, for instance under the skin or into the lungs, it can cause important infections such as boils or pneumonia. Individuals who carry this organism are usually totally healthy, have no problems whatever and are considered simply to be carriers of the organism.
The term MRSA or methicillin resistant Staphylococcus aureus is used to describe those examples of this organism that are resistant to commonly used antibiotics. Methicillin was an antibiotic used many years ago to treat patients with Staphylococcus aureus infections. It is now no longer used except as a means of identifying this particular type of antibiotic resistance.
Individuals can become carriers of MRSA in the same way that they can become a carrier of ordinary Staphylococcus aureus which is by physical contact with the organism. If the organism is on the skin then it can be passed around by physical contact. If the organism is in the nose or is associated with the lungs rather than the skin then it may be passed around by droplet spread from the mouth and nose. We can find out if and where Staphylococcus aureus is located on a patient by taking various samples, sending them to the laboratory and growing the organism. Tests done on any Staphylococcus aureus grown from such specimens can then decide how sensitive the organisms is to antibiotics and if it is a methicillin resistant (MRSA) organism. These test usually take 2-3 days.
Why bother with MRSA?
MRSA organisms are often associated with patients in hospitals but can also be found on patients not in a hospital. Usually it is not necessary to do anything about MRSA organisms. However if MRSA organisms are passed on to someone who is already ill, then a more serious infection may occur in that individual. When patients with MRSA are discovered in a hospital, the hospital will usually try to prevent it from passing around to other patients. This is known as infection control.
How do we prevent the spread of MRSA?
Measures to prevent the spread of organisms from one person to another are called isolation or infection control. The type of infection control or isolation required for any patient depends on the organism, where the organisms is found on an individual and the patient.
The most important type of isolation required for MRSA is what is called Contact Isolation. This type of isolation requires everyone in contact with the patient to be very careful about hand washing after touching either the patient or anything in contact with the patient. If the organism is in the nose or lungs it may also be necessary to have the patient in a room to prevent spread to others by droplet spread. Because dust and surfaces can become contaminated with the organism, cleaning of surfaces are also important. This usually occurs after the patient leaves the hospital.
If a number of patients are infected with the same organism it is possible to nurse them in the same area. On occasions for the sake of other patients it may be necessary to move carriers of MRSA to an isolation unit such as ours which specializes in isolating all types of infections to protect other persons. The medical care of such patients will continue in an isolation unit which are well used to caring for all types of medical and surgical problems associated with infections.
What do visitors need to do?
Provided relatives and friends of patients with MRSA are healthy there is no restriction on visiting and it carries no risk. Visitors are not required to wear special clothing BUT we would ask you to help us prevent this organism spreading around our hospital by keeping the patients' door closed at all times and always washing your hands whenever you leave the room.
What about MRSA at home?
In patients who are otherwise well the organisms often disappear once the patient leaves the hospital. Sometimes they do not however, and this may mean that when a patient has to go back into hospital the isolation precautions need to be used again. Provided everyone at home is healthy special precautions are not required at home.
What can be done about MRSA?
In certain situations it may be a good idea to try to get rid of the organism from a patient and this can be done with various creams and shampoos or on occasions combinations of antibiotics taken by mouth or by injection depending on the health of the patient.
