Methicillin-resistant Staphylococcus 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. Methicillin-resistant Staphylococcus aureus (MRSA) is usually acquired during exposure to hospitals and other healthcare facilities, and causes a variety of serious healthcare-associated infections.¹

• Methicillin resistance is clinically very important because a single genetic element confers resistance to the the beta-lactam antibiotics, which include penicillins, cephalosporins and carbapenems.²
• In the past 20 to 30 years, 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 1990s.³
• 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-16.⁴

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 2004.⁵

• Methicillin 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 S. aureus bacteraemia laboratory reports and methicillin susceptibility in England and Wales (voluntary reporting scheme) indicates an increase in methicillin resistance from 25% in 1990 to 38% in 2006 (but has remained at approximately 40% since 1999).⁶
• Data for each local Hospital Trust is also available from the Department of Health.⁷

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 contacts.⁸
• 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 hours.⁹
• 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 precautions¹⁰ and isolation¹¹ 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 hygiene.²
• 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 endemic.²
• Patients colonised or infected with MRSA should, whenever possible be placed in a separate room, or kept with other patients who have MRSA.²
• 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 removal.²
• 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 MRSA.²

Drugs¹

• Before treating, clinicians should seek advice from a local microbiologist.
• Skin and soft tissue infections:
  • If MRSA is suspected because of previous colonisation/isolation, or surgical/healthcare-related, it is very important to collect a microbiology sample.
  • If MRSA is isolated or strongly suspected, treat with rifampicin with either sodium fusidate, doxycycline or trimethoprim. Linezolid can be used following discussion with Consultant Microbiologist or Infectious Disease physician.
• Serious and deep-seated MRSA infections:
  • Suspected serious and deep-seated MRSA infections should be assessed and treated in hospital.
  • MRSA pneumonia: linezolid plus clindamycin, with or without rifampicin.
  • For other deep-seated MRSA infections, treat with:
    • First-line: Either teicoplanin or vancomycin plus one of the following: gentamicin, rifampicin or sodium fusidate.
    • Second-line: Linezolid.
    • Alternatives: Daptomycin is licensed for SSTIs, and for bacteraemia and right-sided endocarditis due to S. aureus. Tigecycline is licensed for complicated SSTIs.
  • Although most supporting evidence is anecdotal, the use of immunoglobulin (IVIG) should be considered in severe sepsis and necrotizing pneumonia known or suspected to be due to S. aureus.
• MRSA in urine:
  • Antibiotics are unlikely to clear MRSA in the presence of a urinary catheter. There is no good evidence that catheter changes need to be covered with appropriate antibiotic prophylaxis to prevent catheter-related urinary tract infections.
  • A significant MRSA urinary tract infection with systemic symptoms and the presence of white cells in the urine is likely to require systemic antibiotic treatment. In patients with normal renal function (but not children), doxycycline or tetracycline, or trimethoprim or nitrofurantoin.
• Pre-surgical prophylaxis:¹² Prophylaxis with vancomycin or teicoplanin (alone or in combination with another antibacterial active against other pathogens) is appropriate for patients undergoing surgery if:
  • There is a history of MRSA colonisation or infection without documented eradication.
  • There is a risk that the patient’s MRSA carriage has recurred.
  • The patient comes from an area with a high prevalence of MRSA.

Nasal carriage of MRSA¹²

• Elimination of nasal staphylococci can be achieved by nasal chlorhexidine and neomycin creams but re-colonisation often occurs.
• A nasal ointment containing mupirocin can be used for eradication of nasal carriage of MRSA. If the MRSA strain is mupirocin-resistant or does not respond after 2 courses of treatment, alternative products such as chlorhexidine and neomycin cream should be considered.
• Aquasept skin cleanser is recommended for eradication of skin carriage of MRSA.¹²

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 S. 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 infection.¹³
• Applying topical treatments to reduce skin carriage.
• Keeping the environment as clean and dry as possible.¹⁴
• Wear gloves when managing wounds. After removing gloves, wash hands with soap and warm water, or use alcohol-based hand sanitiser.
• 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.