🦠 Meticillin-resistant Staphylococcus aureus (MRSA) is a strain of Staphylococcus aureus resistant to beta-lactam antibiotics because of altered penicillin-binding proteins. Many people carry S. aureus harmlessly on the skin or in the nose, but MRSA is important because it can spread in healthcare settings and cause severe infection in vulnerable patients. Always distinguish colonisation from active infection.
📖 About
- MRSA = S. aureus resistant to meticillin and effectively resistant to standard anti-staphylococcal beta-lactams such as flucloxacillin and co-amoxiclav.
- Colonisation is commoner than invasive disease and may involve the nose, groin, axillae, perineum, wounds, or skin.
- Colonisation alone usually causes no symptoms, but it can act as a reservoir for transmission and later infection.
- MRSA remains particularly important in hospitals, care homes, patients with wounds or devices, and immunocompromised people.
🧬 Aetiology & Resistance Mechanism
- The usual mechanism is acquisition of the mecA gene, producing PBP2a, which has low affinity for beta-lactam antibiotics.
- Many MRSA strains also carry resistance to other antibiotic classes, which narrows treatment choices.
- Therapy should therefore be guided by microbiology results, site of infection, severity, and local resistance patterns.
👥 Patients at Risk
- Frail older adults and people with multiple comorbidities
- Long-stay inpatients, ICU patients, and recent hospital exposure
- People with invasive devices such as urinary catheters, central lines, prosthetic joints, or vascular grafts
- Surgical patients and people with chronic wounds or ulcers
- Immunocompromised patients, including those on chemotherapy or long-term corticosteroids
🧪 Colonisation versus infection
- Colonisation: positive screening swab but no local or systemic signs of infection.
- Infection: positive cultures together with cellulitis, wound infection, pneumonia, bacteraemia, sepsis, bone/joint infection, or other clinical features.
- Do not treat a positive swab alone as invasive infection.
🧴 Decolonisation
- Do not routinely decolonise asymptomatic MRSA carriers in the community.
- Decolonisation may be considered in selected situations, for example recurrent infection, household transmission, or specialist advice.
- For surgery where S. aureus is a likely cause of surgical site infection, NICE recommends considering nasal mupirocin with a chlorhexidine body wash before the procedure, taking into account procedure type, patient risk factors, and local policy.
- Hospitals often use local decolonisation protocols for known carriers, commonly including nasal mupirocin and an antiseptic body wash.
💊 Common decolonisation approach in hospitals (local-policy based)
- Nasal mupirocin applied to both nostrils for a short course (often 5 days).
- Chlorhexidine or other antiseptic body wash daily for several days.
- Re-screening practices vary and should follow local infection-control policy.
- Do not overuse mupirocin because resistance can emerge.
💉 Management of active infection
- Management depends on the site and severity of infection.
- Source control is essential: drain abscesses, remove infected lines if appropriate, debride infected tissue, and assess prosthetic material.
- For serious MRSA infection, treatment is usually directed by microbiology / infectious diseases.
- NICE-linked guidance for severe skin infection lists vancomycin or teicoplanin for suspected or confirmed MRSA, and linezolid if glycopeptides cannot be used, with specialist input.
⚠️ Important clinical contexts
- MRSA bacteraemia: requires urgent IV antibiotics in secondary care and careful search for a source such as line infection, endocarditis, bone/joint infection, or deep abscess.
- MRSA pneumonia: may occur post-influenza or in hospitalised patients; treatment depends on severity and local specialist advice.
- Bone, joint, or prosthetic infection: prolonged antibiotics and often surgical input are needed because of biofilm formation.
- Skin and soft tissue infection: severity determines whether incision and drainage alone, oral treatment, or IV anti-MRSA therapy is required.
🫁 Notes on key MRSA-active agents
- Vancomycin: standard IV option for many serious MRSA infections; requires drug-level and renal monitoring.
- Teicoplanin: another glycopeptide used in many UK hospitals, often with easier dosing.
- Linezolid: active against MRSA and available orally and IV; useful in selected cases but requires caution because of haematological and interaction risks.
- Daptomycin: active against MRSA bacteraemia and some deep infections, but not for pneumonia because it is inactivated by lung surfactant.
🧼 Infection prevention and control
- Hand hygiene remains the single most important measure to reduce spread.
- Use appropriate barrier precautions and follow local isolation / cohorting policy.
- Screening practices vary by setting and local policy, especially for high-risk admissions and certain surgical pathways.
- Device care, wound care, and antimicrobial stewardship are central to reducing MRSA burden.
💡 Clinical Pearl:
A positive MRSA swab does not automatically mean infection.
Think: colonisation = infection-control issue; infection = clinical syndrome + source control + targeted antibiotics.
For surgery, NICE supports considering nasal mupirocin plus chlorhexidine wash where S. aureus surgical-site infection risk is relevant.
📚 References
