Description

• 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 generally 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 from 2000 until 2010 to 2013 when it plateaued for adults and decreased for children.
• CA-MRSA typically causes mild to moderate SSTIs (abscesses, furuncles, and carbuncles).
• Severe or invasive CA-MRSA disease is less frequent but can include:
  • Osteomyelitis
  • Sepsis
  • Septic thrombophlebitis
  • Necrotizing fasciitis
  • Necrotizing pneumonia with abscesses
• Although less frequent, HA-MRSA can still cause SSTIs in the community.
• System(s) affected: skin, soft tissue

Epidemiology

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

Incidence

• SSTI incidence for adult ambulatory care peaked in 2010 at 35 per 1,000 population and has since plateaued.
• SSTI incidence for pediatric ambulatory care visits peaked in 2011 at 26 per 1,000 population, decreasing to 13 per 1,000 in 2015.
• The incidence of MRSA-related hospitalizations decreased from 2010 to 2014.
• Among people who inject drugs, the incidence of MRSA-related skin abscesses is increasing. Patients should receive substance misuse disorder care and be linked with syringe exchange programs.

Prevalence

• 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 staphylococcal cassette cartridge (contains the methicillin-resistant gene mecA)

Risk Factors

~50% of patients have no obvious risk factor. Recognized risk factors include:

• Antibiotic use in the past month, particularly cephalosporins and fluoroquinolones
• Abscess; reported “spider bite”
• Intravenous (IV) or intradermal drug use, HIV infection
• Hemodialysis catheter presence, history of MRSA infection
• Close contact with a similar infection; children, particularly in daycare centers
• Resident in long-term care facility, competitive athletes, incarceration

General Prevention

• Colonization (particularly of the anterior nares) is a risk factor for subsequent S. aureus infection. It is unclear whether this is similar for CA-MRSA. Oropharyngeal and inguinal colonization are equally prevalent.
• CA-MRSA is transmitted easily through environmental and household contact.
• CDC guidance for prevention of MRSA in athletes: http://www.cdc.gov/mrsa/community/team-hc-providers/advice-for-athletes.ht...

Commonly Associated Conditions

Many patients are otherwise healthy.