Community Acquired Methicillin-Resistant Staphylococcus Aureus (CA-MRSA) Skin Infections
- 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:
- 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
- Predominant age: all ages, generally younger
- Predominant sex: female > male
- 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 care for substance misuse and linked with syringe exchange programs.
- 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)
~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
- 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.
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