Methicillin-Resistant Staphylococcus Aureus (MRSA) Skin Infections

Methicillin-Resistant Staphylococcus Aureus (MRSA) Skin Infections is a topic covered in the 5-Minute Clinical Consult.

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  • Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) has unique properties that allow the organism to cause skin and soft tissue infections (SSTIs) in healthy hosts:
    • CA-MRSA has a different virulence and disease pattern than hospital-acquired MRSA (HA-MRSA).
  • CA-MRSA infections impact patients who have not been recently (<1 year) hospitalized or had a medical procedure (e.g., dialysis, surgery, catheters).
  • Incidence of CA-MRSA increased in the United States before plateauing between 2005 and 2010.
  • CA-MRSA typically causes mild to moderate SSTIs (abscesses, furuncles, and carbuncles):
    • Severe or invasive CA-MRSA disease is less frequent but can include:
      • Necrotizing pneumonia with abscesses
      • Necrotizing fasciitis
      • Septic thrombophlebitis
      • Sepsis
      • Osteomyelitis
  • Although less frequent, HA-MRSA can still cause SSTIs in the community.
  • System(s) affected: skin, soft tissue


  • Predominant age: all ages, generally younger
  • Predominant sex: female > male

  • 316/100,000/year (2004 to 2005)
  • 46/100,000 per year pediatric MRSA SSTI hospitalizations
  • The incidence of MRSA-related hospitalizations decreased from 2010 to 2014.
  • The incidence of MRSA-related skin abscesses among people who inject drugs is increasing.
  • Local epidemiology patterns vary.
  • 25–30% of U.S. population colonized with S. aureus; up to 7% are colonized with MRSA.
  • CA-MRSA isolated in ~60% of SSTIs presenting to emergency departments (range 15–74%)
  • CA-MRSA accounts for up to 75% of all community staphylococcal infections in children.

Etiology and Pathophysiology

  • First noted in 1980. Current epidemic began in 1999. The USA300 clone is predominant.
  • CA-MRSA is distinguished from HA-MRSA by
    • Lack of a multidrug-resistant phenotype
    • Presence of exotoxin virulence factors
    • Type IV Staphylococcus cassette cartridge (contains the methicillin-resistant gene mecA)

Risk Factors

  • ~50% of patients have no obvious risk factor.
  • Antibiotic use in the past month
  • Abscess
  • Reported “spider bite”
  • Intravenous (IV) drug use
  • History of MRSA infection
  • Close contact with a similar infection
  • Children, particularly in daycare centers
  • Competitive athlete
  • Incarceration
  • Hospitalization in the past 12 months

General Prevention

  • Colonization (particularly of the anterior nares) is a risk factor for subsequent S. aureus infection. Not certain if similar for CA-MRSA. Oropharyngeal and inguinal colonization are equally prevalent.
  • CA-MRSA transmitted easily through environmental and household contact
  • Health care workers are a primary MRSA vector for hospitalized patients, reinforcing the need for meticulous cleaning of hands and medical equipment.
  • Vaccine under development
  • CDC guidance for prevention of MRSA in athletes:

Commonly Associated Conditions

Many patients are otherwise healthy.

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