MRSA (Methicillin-resistant Staphylococcus aureus) Infection

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management | References

Definition

MRSA (Methicillin-resistant Staphylococcus aureus) is a type of staphylococcal bacteria that is resistant to several widely used antibiotics, making infections difficult to treat. It is known for causing infections in different parts of the body, including the skin, bloodstream, lungs, and surgical sites.

Aetiology

MRSA is caused by Staphylococcus aureus bacteria that have acquired resistance to methicillin and other beta-lactam antibiotics. Transmission occurs through:

• Direct skin-to-skin contact
• Contact with contaminated surfaces or objects
• Healthcare-associated transmission in hospitals and other healthcare settings

Pathophysiology

The pathophysiology of MRSA infection involves:

• Colonisation of the skin or mucous membranes without causing symptoms (asymptomatic carriers)
• Invasion through breaks in the skin or mucous membranes, leading to localised or systemic infections
• Production of toxins and enzymes that facilitate tissue invasion and damage
• Development of biofilms that protect the bacteria from the immune response and antibiotic treatment

Risk Factors

• Hospitalisation or residence in long-term care facilities
• Invasive devices such as catheters or surgical implants
• Recent antibiotic use
• Chronic illness or immunosuppression
• Close contact with someone infected or colonised with MRSA
• Poor hygiene practices

Signs and Symptoms

The signs and symptoms of MRSA infection can vary depending on the site of infection and may include:

• Skin infections: Red, swollen, and painful areas on the skin, often with pus or other drainage. Commonly presents as abscesses, boils, or cellulitis.
• Respiratory infections: Cough, fever, chills, and difficulty breathing if the lungs are involved (pneumonia).
• Bloodstream infections: Fever, chills, low blood pressure, and signs of sepsis.
• Surgical site infections: Redness, pain, swelling, and drainage at the surgical site.

Investigations

Specific investigations to diagnose MRSA infection include:

• Microbiological culture: Culturing samples from the infected site (e.g., wound swab, blood, sputum) to identify MRSA.
• Antibiotic susceptibility testing: To determine which antibiotics the MRSA strain is sensitive to.
• Full blood count (FBC): To check for elevated white blood cell count and other markers of infection.
• Imaging: X-rays, ultrasound, or CT scans may be used to assess the extent of infection and detect complications.

Management

Primary Care Management

• Antibiotics: Oral antibiotics that are effective against MRSA, such as doxycycline, clindamycin, or trimethoprim-sulfamethoxazole (TMP-SMX).
• Incision and drainage: For abscesses, incision and drainage may be necessary to remove pus and reduce the bacterial load.
• Hygiene measures: Emphasising proper hand hygiene, wound care, and cleaning of contaminated surfaces to prevent spread.

Specialist Management

• Intravenous antibiotics: For severe or systemic infections, intravenous antibiotics such as vancomycin, linezolid, or daptomycin may be required.
• Hospitalisation: For severe cases, particularly those with complications such as sepsis or endocarditis.
• Infection control measures: Isolation precautions and strict adherence to infection control practices in healthcare settings to prevent transmission.
• Monitoring and follow-up: Regular monitoring for response to treatment and early detection of any complications.

References

1. NHS (2024) MRSA infection. Available at: https://www.nhs.uk/conditions/mrsa/ (Accessed: 24 June 2024).
2. Centers for Disease Control and Prevention (2024) Methicillin-resistant Staphylococcus aureus (MRSA). Available at: https://www.cdc.gov/mrsa/index.html (Accessed: 24 June 2024).
3. World Health Organization (2024) Antimicrobial resistance. Available at: https://www.who.int/news-room/fact-sheets/detail/antimicrobial-resistance (Accessed: 24 June 2024).
4. British Medical Journal (2024) MRSA: clinical features, diagnosis, and management. Available at: https://www.bmj.com/content/350/bmj.h1834 (Accessed: 24 June 2024).

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