What is Methicillin-resistant Staphylococcus aureus (MRSA)?

Methicillin-Resistant Staphylococcus aureus (MRSA)

MRSA is a type of Staphylococcus aureus bacteria that has developed resistance to methicillin and other beta-lactam antibiotics, causing infections ranging from skin and soft tissue infections to life-threatening invasive disease. 1

Definition and Characteristics

MRSA is characterized by:

• A strain of Staphylococcus aureus that has acquired resistance to methicillin and other beta-lactam antibiotics
• Resistance mediated by the mecA gene
• Often associated with the Panton-Valentine leukocidin (PVL) toxin in community-acquired strains 1

Types of MRSA

There are two main types of MRSA:

1. Healthcare-Associated MRSA (HA-MRSA):

   • Typically multi-drug resistant
   • Found in healthcare settings such as hospitals and long-term care facilities
   • Requires more complex treatment approaches 1

2. Community-Acquired MRSA (CA-MRSA):

   • Generally susceptible to multiple antibiotics
   • Increasingly common in community settings
   • Often causes skin and soft tissue infections 1

Clinical Presentation

MRSA can cause a wide spectrum of infections:

• Skin and soft tissue infections (most common)
• Bacteremia (75% of invasive cases)
• Pneumonia
• Bone and joint infections
• Endocarditis
• CNS infections
• Toxic shock syndrome 1

Severe complications can include:

• Sepsis with purpura fulminans
• Waterhouse-Friderichsen syndrome
• Necrotizing fasciitis
• Pyomyositis 1

Epidemiology

• MRSA prevalence varies significantly by region
• In the United States, an estimated 94,360 cases of invasive MRSA disease occurred in 2005 1
• Higher colonization rates in certain populations:
  • Children under 2 years old
  • Athletes (especially in contact sports)
  • Injection drug users
  • Individuals with recent antibiotic use 1

Prevention and Control

Key prevention strategies include:

1. Personal Hygiene:

   • Regular handwashing
   • Immediate showering after sports/activities 1

2. Environmental Measures:

   • Regular cleaning of high-touch surfaces
   • Disinfection of shared equipment 1

3. Decolonization Strategies (for recurrent infections):

   • Nasal decolonization with mupirocin
   • Topical body decolonization with chlorhexidine or dilute bleach baths 1

4. Early Detection and Isolation:

   • Recommended by all guidelines as a general principle 2

Treatment Approaches

Treatment depends on the type and severity of infection:

1. For Skin and Soft Tissue Infections:

   • Incision and drainage for abscesses
   • Antibiotic therapy based on local MRSA prevalence
   • Treatment duration typically 7-14 days 1

2. For MSSA (Methicillin-Susceptible S. aureus):

   • Penicillinase-resistant penicillins (flucloxacillin, dicloxacillin) remain first choice
   • First-generation cephalosporins, clindamycin, or erythromycin for less serious infections 3

3. For MRSA Infections:

   • Serious infections: Vancomycin or teicoplanin (if vancomycin allergic)
   • Less serious infections: Lincosamides (clindamycin, lincomycin) or cotrimoxazole
   • Alternative agents for resistant strains: Linezolid, daptomycin, quinupristin-dalfopristin, and telavancin 1, 3

Special Considerations

• Doxycycline should not be used in children under 8 years of age
• Athletes can return to play after completing at least 72 hours of antibiotic therapy and meeting specific criteria
• Symptomatic contacts should be evaluated and treated
• Asymptomatic household contacts should be considered for screening 1

Emerging Resistance Concerns

Some strains have developed reduced susceptibility or resistance to glycopeptides:

• VISA (Vancomycin-Intermediate S. aureus)
• VRSA (Vancomycin-Resistant S. aureus)

These highly resistant infections may require combination therapy or newer antimicrobial agents 4