Methicillin Resistant Staph. Aureus (MRSA)

Staphylococcus aureus is a gram-positive bacterium that colonises the skin and is present in the anterior nares in about 25-30% of healthy people. Meticillin resistance is clinically very important because a single genetic element confers resistance to the the beta-lactam antibiotics, which include penicillins, cephalosporins and carbapenems¹.

In the past 20 to 30 years, meticillin-resistant Staphylococcus aureus (MRSA) strains have been present in hospitals and have become a major cause of hospital-acquired infection. Community-acquired MRSA emerged worldwide in the late 1990s².

Some strains of MRSA, known as epidemic strains or EMRSA, are more likely to spread. To date, 16 epidemic strains have been identified in the UK and the most common strains to affect hospitals have been EMRSA-15 and EMRSA-16³.

Spread from person to person is by direct contact with the skin or via a contaminated environment or equipment. Staphylococci that are shed into the environment may survive for long periods in dust. Skin scales may contaminate if they become airborne, e.g. during activities such as bed making, or if the affected person is heavily colonised or has a condition such as eczema which causes shedding of high numbers of organisms.
The Department of Health issued The Matron's Charter; An Action Plan for Cleaner Hospitals in October 2004⁴.

• Meticillin resistance rates of S. aureus vary considerably between countries, with a high prevalence in the United States and southern Europe (over 20%) and a low prevalence in northern Europe (below 5%)
• Data from the Staphylococcus aureus bacteraemia laboratory reports and meticillin susceptibility in England and Wales (voluntary reporting scheme) indicates an increase in meticillin resistance from 25% in 1990 to 41% in 2003⁵
• Data for each local Hospital Trust is also available from the Department of Health⁶.

Risk Factors

• MRSA is one of the most prevalent micro-organisms involved with healthcare-associated infections. It is usually confined to hospitals and in particular to vulnerable or debilitated patients.
• Some nursing homes have experienced problems with MRSA
• MRSA does not pose a risk to hospital staff (unless they are suffering from a debilitating disease) or family members of an affected patient or their close social or work contacts⁷
• Risk factors for community acquired MRSA skin infection include exposure to prisons, occupations or recreational activities with regular skin-to-skin contact (e.g. wrestling), exposure to someone with MRSA or prior incarceration; exposure to antibiotics, recurrent skin infections and living in a crowded environment.

• Rapid diagnosis in hospital is essential in order to start appropriate treatment early and also initiate procedures to prevent the spread of MRSA
• Molecular testing methods are now available to identify MRSA within several hours⁸
• MRSA DNA has now been decoded and a rapid (2 hour) genetic fingerprint identification test is currently being piloted in 2 UK hospitals.

There is evidence that concerted efforts that include surveillance cultures, contact precautions⁹ and isolation¹⁰ in hospitals can reduce MRSA even in endemic settings. No one measure to control the spread of MRSA has proved to be effective. However comprehensive MRSA-control programmes that have included screening cultures to detect patients (and in many instances staff ) colonised with MRSA, use of contact precautions, appropriate hand hygiene, automatic alerts of readmission of colonised patients have reported success in controlling or reducing transmission of MRSA and also reduced acquisition of MRSA in high-risk units in hospitals.

• Health-care workers who are nasal carriers can serve as sources of MRSA transmission, although they are not nearly as important a reservoir as are colonised or infected patients. Failure to identify health-care workers who are persistently colonised or infected can lead to continuing transmission despite implementation of barrier precautions and hand hygiene¹.
• Screening of patients by culture of samples from body sites such as the anterior nares alone will identify 80%, and screening from additional body sites will increase the sensitivity to over 92%. There is evidence that screening of high-risk patients, combined with other measures such as contact precautions, appropriate hand hygiene, and education of personnel, can reduce transmission of MRSA, even in facilities where it is highly endemic¹.
• Patients colonised or infected with MRSA should, whenever possible be placed in a separate room, or kept with other patients who have MRSA¹
• Transient contamination of health-care workers' hands is widely believed to be the predominant method by which MRSA is transmitted to patients. Because health-care workers' hands can become contaminated even when gloves are worn, hand hygiene is recommended after glove removal¹.
• There is no consensus about the indications for topical intranasal therapy, or systemic antibiotics to
  patients and staff who are colonised. Mupirocin often fails to eradicate carriage. Widespread or long-term use of mupirocin should be avoided because it may lead to the emergence of mupirocin-resistant strains of MRSA¹.

Drugs

BNF recommendations¹¹:

• Some of these organisms may be sensitive to vancomycin or teicoplanin
• Strains may be susceptible to rifampicin, sodium fusidate, tetracyclines, aminoglycosides, macrolides, and clindamycin
• Rifampicin or sodium fusidate should not be used alone because resistance may develop rapidly
• Trimethoprim alone may be used for urinary-tract infections caused by some MRSA strains
• Linezolid and the combination of the streptogramin antibiotics quinupristin and dalfopristin are active against MRSA but these antibacterial drugs should be reserved for organisms resistant to treatment with other antibacterials or for patients who cannot tolerate other antibacterial drugs
• Treatment should be guided by the sensitivity of the infecting strain
• Nasal carriage of MRSA:
  • In hospital or in care establishments, mupirocin nasal ointment should be reserved for the eradication of nasal carriage of MRSA. To avoid the development of resistance, the treatment course should not exceed 7 days and the course should not be repeated on more than one occasion.
  • If the MRSA strain is mupirocin-resistant or does not respond after 2 courses, chlorhexidine and neomycin cream may be used.
• Aquasept skin cleanser is recommended for eradication of skin carriage of MRSA¹¹.

Care in the community

• While the risk of serious infection with MRSA is low in the community, it still exists. In 1996, the Department of Health issued guidelines for managing MRSA in nursing and residential homes. This stresses the importance of standard infection control procedures. It also advises against isolating MRSA positive patients in community homes, instead recommending that patients socialise as normal. However, they should not share a room if they have a chronic open wound or invasive device, such as a urinary catheter.
• In the patient's own home there should be no restrictions to a normal life and people with MRSA can work and socialise as usual. They do not need to restrict contact with friends, children or the elderly. If they are admitted to hospital, where the risk of infection is increased, the ward should be informed so the patient is screened on admission and nursed appropriately.
• Community health care workers should practise standard infection control precautions, such as aseptic technique for wound care. They must decontaminate their hands before and after giving care, either by using soap and water or an alcohol hand rub.

MRSA is no more dangerous or virulent than other varieties of Staphylococcus aureus, but it is much more difficult to treat because the range of antibiotics which are effective against it is reduced.

To help prevent the spread of MRSA in a health care setting:

• Hand washing reduces hospital-acquired infection¹²
• Applying topical treatments to reduce skin carriage
• Keeping the environment as clean and dry as possible¹³
• Wear gloves when managing wounds. After removing gloves, wash hands with soap and warm water, or use alcohol-based hand sanitizer.
• Carefully dispose of dressings and other materials that come into contact with blood, nasal discharge, urine, or pus from patients infected with MRSA.
• Clean surfaces in exam rooms with commercial disinfectant or a 1:100 solution of diluted bleach
• Nasal carriage is usually transient, in some cases lasting only a matter of hours. Therefore routine screening of staff for MRSA carriage is not recommended. Pre-employment screening of staff for MRSA carriage is also considered unnecessary but local guidelines may vary.