Staphylococcus aureus: colonisation versus infection Staphylococcus aureus (s.aureus)
is a colonising bacteria: about one third of people are colonised with this bacteria persistently, a further third are colonised intermittently and the final third are rarely or never colonised. The organism is found most commonly in the nostrils but can also live on other parts of the skin as well as mucous membranes, including the throat and vagina. Although s.aureus
can cause infection and illness, the risk of an infection developing in any particular healthy carrier of the organism is low. However, if the protective layers of the body are broken by accidental or surgical wounds, ulcers or medical devices such as intravenous lines, the risk of infection is greatly increased. S. aureus
, therefore, assumes particular significance as a cause of healthcare or hospital associated infection (HCAI).
- Most people who have S. aureus are colonised with it and the bacteria is doing them no harm.
- In a minority of cases, usually when the skin has been breached, S. aureus can enter the body and cause infection.
Staphylococcus aureus and the rise of MRSA
Lots of different strains of S.aureus exist and each strain has different properties which influence its virulence, its ability to transmit from person to person and resistance to antibiotics. When bacteria are exposed to antibiotics, they will only survive if:
- they are naturally resistant to the antibiotic
- they pick up resistant genes from other bacteria
- they mutate to become resistant
When antibiotics were first developed in the 1940s, all strains of S. aureus were sensitive to penicillin, in other words penicillin could kill the bacteria and cure infection. Within 20 years of penicillin becoming available, 95% of S. aureus strains had become resistant to this antibiotic. Methicillin, which was an antibiotic designed to treat these resistant strains, became available in 1960 but, within 1 year, resistant strains were being seen. These strains were termed Methicillin Resistant Staphylococcus Aureus or MRSA for short. Worryingly, the mechanism of resistance involved renders MRSA resistant to all other penicillin-based and cephalosporin antibiotics as well. Moreover, the resistance gene is often carried alongside other resistance genes, meaning that MRSA is often resistant to other antibiotics such as erythromycin, ciprofloxacin, fucidin and tetracycline.
Numerous different MRSA strains have been identified since the 1960s. Some of them are capable of spreading widely and have caused outbreaks of infection; these are termed the epidemic MRSA strains. In the past these strains have almost always been associated with hospital and healthcare settings, although recently distinct strains have emerged causing outbreaks in the community.
The current ‘MRSA problem’ affecting UK hospitals is caused by the epidemic MRSA strains EMRSA-15 and EMRSA-16 and their derivatives which first appeared in south east England in the 1990s. The Royal Free Hospital was among the first to be affected by these strains because it accepted colonised patients from affected hospitals. EMRSA 15 and EMRSA 16 have since spread to all parts of the UK. It is unknown just how many healthy people in the community are colonised with MRSA but studies suggest that it is increasing, and community strains of MRSA are likely to play a larger role in the future.
- MRSA is a strain of S. aureus that has become resistant to some of our commoner antibiotics.
- Most MRSA is seen in hospitals because, traditionally, this is where the most transmissible strains have circulated.
- There are effective antibiotics available to treat MRSA infection.
Is MRSA more dangerous than sensitive Staphylococcus aureus?
There is no evidence that MRSA is more virulent or dangerous than sensitive strains of S. aureus. Because it is resistant to some antibiotics, there is a chance that starting appropriate antibiotic treatment will be delayed.
- MRSA is not more dangerous than normal S. aureus, but there may be a delay in starting an appropriate antibiotic if the patient is not known to have MRSA.
How did I get MRSA?
MRSA is usually spread by hand contact, either as direct contact with a colonised person or via the hands of someone who has recently touched a colonised person and has not washed their hands.
Because the more transmissible, epidemic strains of MRSA are more common in hospital patients than out in the community, you are still more likely to catch MRSA in hospital. This picture is changing and we are seeing more people who are already colonised when they are admitted to hospital; this suggests that MRSA is beginning to transmit more in the community.
- MRSA is usually spread by transmission from one patient to another via the hands of healthcare staff who have not washed their hands.
What happens now that I have MRSA?
Since MRSA is usually spread by hand contact, we will aim to prevent spread to other patients without compromising your care. You will be nursed in a single room; if none are available you will be nursed in a bay with other MRSA colonised patients. Staff will wear disposable aprons when caring for you and they will decontaminate their hands before and after touching you. If appropriate, we will try and eliminate the MRSA from your skin with a five-day decolonisation programme of topical solutions.
If you need to leave the ward for a test or procedure, the staff performing the test will be informed that you are a MRSA carrier so that they can clean the equipment thoroughly before another patient is seen.
If you need to be transferred to another hospital, we will inform the hospital in question so that they can arrange a single room for you. This may delay your transfer but we will do all we can to ensure your transfer is as soon as possible.
- Patients with MRSA are nursed in ‘isolation’ with infection control precautions.
- If appropriate, elimination of MRSA carriage is attempted using topical decolonisation.
Once I’ve got it, can I get rid of MRSA?
It is possible to eliminate surface MRSA carriage using a topical decolonisation programme. The programme involves application of antiseptic bodywash, shampoo, mouthwash and an antibiotic nasal ointment for five consecutive days. Once the programme is completed, surface screening swabs are taken from both the nose and the groin area at five to seven-day intervals. A patient is considered free of MRSA only if three sequential sets of swabs are negative.
The decolonisation programme is not 100% effective. It will eliminate MRSA in up to 75% of patients. It is less likely to work if there are skin areas where the MRSA can hide. For instance, a fresh surgical wound or chronic leg ulcer contains lots of crevices which the topical treatments cannot penetrate. The same goes for intravenous lines, stoma sites, PEG sites urinary catheters as these devices also provide the MRSA with somewhere to hide and it is very difficult to eradicate MRSA from plastic using the topical preparations which are safe to use on the skin.
If you are due to have an operation, the decolonisation programme will begin five days before surgery so that, even if complete eradication is not possible, the amount of MRSA on the skin will be at the lowest level possible when the operation is performed.
Occasionally, the decolonisation programme will reduce the MRSA to a low level that will not be detected from the screening swabs but it may still be present on the patient. So it is still important that, if you are admitted to hospital, you tell the hospital staff that you have previously been colonised with MRSA even if you have been successfully decolonised. You should then be nursed in a side room until swabs are taken to see if the MRSA has come back.
- A topical decolonisation programme may eliminate MRSA from the skin.
- Patients with open wounds or invasive devices are less likely to be cleared of MRSA.
- MRSA patients who are due to have surgery should start the decolonisation programme just before the operation so that the risk of MRSA wound infection is reduced.
Can MRSA be prevented?
Most MRSA is preventable. The 30% of the population who are prone to carrying S. aureus are more likely to pick up strains of the bacteria circulating in the environment so, now that we are seeing MRSA outside hospitals, it is unlikely that we will ever get rid of MRSA altogether.
The main route of spread of MRSA in hospitals is transmission from one patient to another via the hands of healthcare staff. This transmission can be virtually eliminated if staff clean their hands between patients. You should not catch MRSA in hospital because staff should be cleaning their hands between leaving one patient and touching another. Sometimes staff are very busy and may forget to clean their hands. Please ask a member of staff to clean their hands before touching you if they have not done so.
- Most MRSA carriage can be prevented if staff wash their hands before and after touching a patient.
Will MRSA affect my friends and family?
MRSA will not harm healthy people who come to visit you (including young children and pregnant women). Visitors should wear the disposable gloves and aprons provided. When leaving, they should dispose of the gloves and aprons in the nearest bin and wash their hands. They should not visit other people on the ward or use the communal facilities such as ward kitchen or day room. If your visitors have any concerns, they should speak to the nurse-in-charge or the infection control nurse.
- MRSA should not be a risk to your friends and family, and should not prevent them from visiting, as long as they follow infection control precautions.
Why are MRSA rates high at the Royal Free?
The Royal Free has a high number of MRSA-colonised patients because the hospital is home to a number of specialised services that deal with particularly complex medical problems. Patients have often been in hospital many times before and some have attended other hospitals before arriving at the Royal Free. These patients are also at high risk of MRSA infection because they often undergo multiple invasive procedures which breach the body’s protective barriers and others have impaired immune systems so their ability to fight off infection is poor.
- MRSA rates are high at the Royal Free because it is a large specialist centre which deals with long-term patients who have attended multiple hospitals and have complex medical problems putting them at risk of hospital-acquired infections.
What is the Royal Free doing to reduce the spread of MRSA?
As mentioned previously, the best way of preventing MRSA spreading from patient to patient is for healthcare staff to wash their hands after touching one patient and before touching another patient. All Royal Free staff now receive regular mandatory training in infection control to reinforce good hand hygiene and the hospital has also taken part in the National Patient Safety Agency’s ‘Clean your Hands’ campaign since 2005. This campaign encourages good hand hygiene by providing alcohol hand gel dispensers and promotional hand washing posters in every clinical area of the hospital.
Isolation of MRSA positive patients is also important in limiting spread of MRSA. A quarter of the hospital’s beds are in single rooms; this allows potentially infectious patients to be isolated from others and prompts healthcare staff to wash their hands before entering and leaving the room. Unfortunately, there are not enough single rooms to house all our infections and MRSA patients are often nursed in a ‘cohort’ MRSA bay – that means with other patients who are infected. The trust has a robust isolation policy and there are twice daily meetings between the infection control team and bed managers to discuss side room allocation and cohorting.
All patients at high-risk of carrying MRSA are screened for MRSA on admission to hospital. This includes anyone arriving from another hospital or nursing home, anyone admitted to ITU, anyone who has previously been colonised with MRSA and anyone who has been an in-patient in the past year. We regularly screen our ITU patients and renal patients whom we know are our highest-risk groups for hospital-acquired infection. We also screen pre-operative orthopaedic patients, where the risk of having MRSA may be low, but where the consequences of getting MRSA infection at the operative site could be devastating.
We have recently implemented a new rapid laboratory test for MRSA. Previously laboratory tests took about three days to confirm that a patient was colonised with MRSA. The new test is able to identify MRSA carriers in less than four hours. This allows us to identify carriers more quickly and isolate them appropriately, which reduces the risk of a carrier’s MRSA being transferred to other patients.
For those patients who are found to be carrying MRSA, we have a dedicated MRSA liaison nurse who ensures infection control precautions are in place, deals with any queries and fears that the patient may have and coordinates the topical decolonisation programme.
In January 2006 the trust signed up to the Department of Health ‘Saving Lives’ delivery programme which makes tackling MRSA and other healthcare-associated infections a high priority for everyone working within the hospital, including managerial staff, and highlights a number of high-impact interventions to be targeted for improvement.
The environment is also a potential reservoir for MRSA. Every month, the Patient and Public Involvement (PPI) Forum inspect the hospital. Members of the forum are not employed by the hospital and can inspect any clinical area without warning. Their inspections assess the cleanliness of the environment.
- Improving staff hand hygiene with mandatory training in infection control and the ‘Clean Your Hands’ campaign.
- A dedicated MRSA liaison nurse to ensure adherence to infection control precautions and coordinate decolonisation.
- Detection of MRSA carriers with admission screening of all high-risk patients, regular screening of ITU and renal patients, and the introduction of a rapid screening test allowing us to identify MRSA positive patients within 4 hours and act appropriately.
- The Royal Free is signed up the Department of Health’s ‘Saving Lives’ delivery programme to reduce healthcare-associated infections.
- Monthly ward inspections from the Patient and Public Involvement forum.
Are these measures working?
MRSA bacteraemia, where MRSA has entered through the protective layers of the body and into the bloodstream, is used as a marker of MRSA hospital acquired infection. Since April 2001, all hospitals have had to report their MRSA bacteraemia rates. As expected, these data have revealed higher numbers of bacteraemia in large, specialist centres such as the Royal Free. Nevertheless, it has also shown that the Royal Free has achieved a downward trend since reporting began.
The trust has also shown solid improvement in cleanliness and hygiene as demonstrated by monthly Patient and Public Involvement (PPI) forum inspections and recent Patient Environment Action Team (PEAT) audits. Further Information top