Staphylococcus aureus is a Gram-positive bacterium that colonises the skin, and nasal carriage occurs in about 25-30% of healthy people. Meticillin-resistant S. aureus (MRSA) is usually acquired during exposure to hospitals and other healthcare facilities, and causes a variety of serious healthcare-associated infections.¹ However, 1-3% of the total population are colonised with MRSA and in most cases no treatment is necessary as colonisation does not lead to any harmful infection.²

Meticillin resistance is clinically very important because a single genetic element confers resistance to the the beta-lactam antibiotics, which include penicillins, cephalosporins and carbapenems.³ In the past 20 to 30 years, MRSA strains have been present in hospitals - hospital-acquired MRSA (HA-MRSA); they have become a major cause of hospital-acquired infection. Community-acquired MRSA (CA-MRSA) emerged worldwide in the late 1990s.⁴

Most MRSA infections in the UK that appear to have a community onset occur in patients who are found to have had direct or indirect contact with hospitals, care homes or other healthcare facilities. These MRSA strains are typical of the local HA-MRSA and may be carried asymptomatically by patients for months after discharge. However, new strains of MRSA have recently emerged that cause infections in community patients who have no previous history of direct or indirect healthcare contact.

CA-MRSA strains are genetically and phenotypically distinct from HA-MRSA. They often produce Panton-Valentine leukocidin (PVL) and PVL-producing strains of CA-MRSA appear to be associated with increased risk of transmission, complications and hospitalisation.¹ See also separate article PVL-positive Staphylococcus Aureus.

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

Epidemiology

The surveillance of MRSA in the UK is a mandatory scheme run by the Department of Health.⁶

• About 30% of the UK population are colonised with S. aureus, and 1-3% of the total population are colonised with MRSA.²
• Meticillin resistance rates of S. aureus vary considerably between countries, with a high prevalence in the USA and southern Europe (over 20%) and a low prevalence in northern Europe (below 5%).
• Data from the S. aureus bacteraemia laboratory reports and meticillin susceptibility in England, Wales and Northern Ireland (voluntary reporting scheme) indicate an increase in meticillin resistance from 4% in 1993 to 30% in 2007 (but resistance was 36-39% between 2001 and 2006).⁷ The percentage meticillin resistance has further reduced to 24.3% in 2008 and 19.3% in 2009.⁸
• Data for each local Hospital Trust is also available from the Department of Health.⁹

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 to family members of an affected patient or to their close social or work contacts.⁶
• Healthcare-associated MRSA infections arise in individuals with predisposing risk factors, e.g. surgery or presence of an indwelling medical device, but many community-associated MRSA infections arise in otherwise healthy individuals who do not have such risk factors.¹⁰ Specific risk factors for MRSA include:²
  • Critical or chronic illness, if also elderly or debilitated.
  • Presence of surgical wounds, open ulcers, intravenous lines, and catheter lines.
  • Presence of an infected pressure sore.
  • History of MRSA colonisation or infection, or recent surgery.
  • Recent discharge from hospital.
  • Regular nursing home contact or a nursing home resident.
  • Recent antibiotic use (especially cephalosporins, fluoroquinolones, and macrolides).
  • Dialysis.
  • Presence of a permanent indwelling urinary catheter.
• Hospital-acquired MRSA (HA-MRSA) carriage has been found to be common at the time of discharge and one study found that transmission occurred in nearly 20% of household contacts (particularly associated with older age).¹¹
• Although HA-MRSA is more common in elderly, debilitated and/or critically or chronically ill patients, community-acquired MRSA (CA-MRSA) is more often seen in young, healthy people; students, professional athletes and military service personnel.¹
• Risk factors for CA-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, intravenous drug abuse, recurrent skin infections and living in a crowded environment.

Investigations

• 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 (polymerase chain reaction (PCR) tests) are now available to identify MRSA within several hours.¹² PCR from culture samples may be used to detect the mecA gene, confirming the presence of MRSA.
• MRSA DNA has now been decoded and a rapid (2-hour) genetic fingerprint identification test is currently being piloted.

Management

There is evidence that concerted efforts that include surveillance cultures, contact precautions¹³ and isolation¹⁴ 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, which have included screening cultures to detect patients (and in many instances staff) colonised with MRSA, use of contact precautions, appropriate hand hygiene, and 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.

• Healthcare 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 healthcare workers who are persistently colonised or infected can lead to continuing transmission despite implementation of barrier precautions and hand hygiene measures.³
• 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.³
• Patients colonised or infected with MRSA should, whenever possible, be placed in a separate room, or kept with other patients who have MRSA.³
• Transient contamination of healthcare workers' hands is widely believed to be the predominant method by which MRSA is transmitted to patients. Because healthcare workers' hands can become contaminated even when gloves are worn, hand hygiene is recommended after glove removal.³
• 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.³

Drugs^1,15

• Before treating, clinicians should seek advice from a local microbiologist. If MRSA is suspected because of previous colonisation/isolation, or is surgical/healthcare-related, it is very important to collect a microbiology sample.
• Rifampicin or sodium fusidate should not be used alone because resistance may develop rapidly.
• Skin and soft-tissue infections:
  • Incision and drainage without the use of antibiotics may be sufficient treatment for small abscesses.
  • A tetracycline alone or a combination of rifampicin and sodium fusidate can be used for skin and soft-tissue infections caused by MRSA; clindamycin alone is an alternative.
  • A glycopeptide (vancomycin or teicoplanin) can be used for severe skin and soft-tissue infections associated with MRSA; linezolid can be used on expert advice if a glycopeptides is not suitable.
  • A combination of a glycopeptide and sodium fusidate or a glycopeptide and rifampicin can be considered for skin and soft-tissue infections that have failed to respond to a single antibacterial.
  • Tigecycline and daptomycin are licensed for the treatment of complicated skin and soft-tissue infections involving MRSA.
• Respiratory tract infections:
  • A tetracycline or clindamycin can be used for bronchiectasis caused by MRSA.
  • A glycopeptide can be used for pneumonia associated with MRSA; if a glycopeptide is unsuitable, linezolid can be used on expert advice.
• Urinary tract infections
  • A tetracycline can be used for urinary-tract infections caused by MRSA; trimethoprim or nitrofurantoin are alternatives.
  • A glycopeptide can be used for urinary tract infections that are severe or resistant to other antibacterials.
• Other infections:
  • A glycopeptide can be used for septicaemia associated with MRSA.
  • Endocarditis: vancomycin and rifampicin.
  • Osteomyelitis: vancomycin.
  • Septic arthritis: vancomycin.
• 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.
• Mupirocin nasal ointment should be reserved for the eradication (in both patients and staff) of nasal carriage of MRSA.

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 healthcare 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.

Prognosis

• 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.

Prevention

All NHS patients going into hospital for a relevant planned procedure are now screened for MRSA beforehand.

• Hand washing reduces hospital-acquired infection.¹⁹
• Applying topical treatments reduces skin carriage.
• Keep the environment as clean and dry as possible.²⁰
• 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 examination 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.

Document references

1. Guidelines for UK practice for the diagnosis and management of methicillin-resistant staphylococcus aureus MRSA infections presenting in the community, Journal of Antimicrobial Chemotherapy (2008)
2. MRSA in primary care, Clinical Knowledge Summaries (January 2009)
3. Grundmann H, Aires-de-Sousa M, Boyce J, et al; Emergence and resurgence of meticillin-resistant Staphylococcus aureus as a public-health threat. Lancet. 2006 Sep 2;368(9538):874-85. [abstract]
4. Vandenesch F, Etienne J; How to prevent transmission of MRSA in the open community? Euro Surveill. 2004 Nov;9(11):5.
5. A matron's charter: An action plan for cleaner hospitals, Dept of Health, October, 2004
6. Staphylococcus aureus and MRSA (various), Health Protection Agency (various dates)
7. Voluntary reporting of Staphylococcus aureus bacteraemia in England, Wales, and Northern Ireland, January-December 2007, Health Protection Agency
8. Voluntary reporting of Staphylococcus aureus bacteraemia in England, Wales and Northern Ireland, 2009, Health Protection Agency
9. Mandatory Bacteraemia Surveillance Scheme - MRSA bacteraemia by NHS Trust: April 2001-March 2005, Dept of Health
10. Deleo FR, Otto M, Kreiswirth BN, et al; Community-associated meticillin-resistant Staphylococcus aureus. Lancet. 2010 May 1;375(9725):1557-68. Epub 2010 Mar 5. [abstract]
11. Lucet JC, Paoletti X, Demontpion C, et al; Carriage of methicillin-resistant Staphylococcus aureus in home care settings: Arch Intern Med. 2009 Aug 10;169(15):1372-8. [abstract]
12. Huletsky A, Giroux R, Rossbach V, et al; New real-time PCR assay for rapid detection of methicillin-resistant Staphylococcus aureus directly from specimens containing a mixture of staphylococci. J Clin Microbiol. 2004 May;42(5):1875-84. [abstract]
13. Muto CA, Jernigan JA, Ostrowsky BE, et al; SHEA guideline for preventing nosocomial transmission of multidrug-resistant strains of Staphylococcus aureus and enterococcus. Infect Control Hosp Epidemiol. 2003 May;24(5):362-86. [abstract]
14. Cooper BS, Stone SP, Kibbler CC, et al; Isolation measures in the hospital management of methicillin resistant Staphylococcus aureus (MRSA): systematic review of the literature. BMJ. 2004 Sep 4;329(7465):533. [abstract]
15. British National Formulary
16. Brady RR, McDermott C, Graham C, et al; A prevalence screen of MRSA nasal colonisation amongst UK doctors in a Eur J Clin Microbiol Infect Dis. 2009 Aug;28(8):991-5. Epub 2009 Feb 24. [abstract]
17. Ludlam HA, Swayne RL, Kearns AM, et al; Evidence from a UK teaching hospital that MRSA is primarily transmitted by the J Hosp Infect. 2010 Mar;74(3):296-9. Epub 2010 Feb 11.
18. Creamer E, Dorrian S, Dolan A, et al; When are the hands of healthcare workers positive for methicillin-resistant J Hosp Infect. 2010 Jun;75(2):107-11. Epub 2010 Mar 17. [abstract]
19. Washing hands reduces hospital-acquired infection, Bandolier, December 2000
20. Guidance for Nursing Staff; Methicillin Resistant Staphylococcus Aureus (MRSA), Royal College of Nursing, 2005

Internet and further reading

• Infection control, prevention of healthcare-associated infection in primary and community care, NICE (2003)

Acknowledgements