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Community Acquired Methicillin Resistant Staphylococcus Aureus CA-MRSA
Physician Guidelines for treatment of CA-MRSA

Epidemiology and Pathogen characteristics

Methicillin resistant Staphylococcus aureus MRSA has become an increasing challenge to Public Health as it continues to develop resistance to newer antibiotics. MRSA is currently thought of as a hospital acquired infection whereas community acquired methicillin resistant Staphylococcus aureus CAMRSA causes illness in persons with no known association with hospitals and healthcare facilities.

Table 1
Traditional MRSA versus Community-acquired MRSA
Traditional MRSA Community-acquired MRSA
Typical patients
Elderly, debilitated, and/or critically or chronically ill
Young, healthy people; high school, college, and professional athletes
Infection site
Bacteremia with no infection focus
Predilection for skin; cellulitis, abscesses; often mistaken for spider bites
Little spread among household contacts
May spread in families and on sports teams
Diagnosis is typically made
in an inpatient setting
in an outpatient setting
Medical History
History of MRSA infection; recent surgery, admission to a hospital or nursing facility, or antibiotic use; dialysis, permanent indwelling catheter
No significant medical history
Virulence factors
Community spread is limited
PVL genes absent
Community spread occurs easily
PVL genes present, predisposing to necrotizing soft tissue infection
Antibiotic susceptibility
Often resistant to fluoroquinolones, aminoglycosides, erythromycin, clindamycin
Resistance usually limited to methicillin and erythromycin
Key: MRSA, methicillin-resistant Staphylococcus aureus; PVL, Panton-Valentine leukocyte.

Community-acquired MRSA's surprising targets Source: Patient Care By: William Schaffner, MD, C. Buddy Creech, MD, Louis D. Saravolatz, MD

Risk Factors

  • Close contact with someone who is colonized or infected with CA-MRSA
  • Exposure to shared sports equipment, towels, clothing or common surfaces i.e. benches, shower floors
  • Participation in sports with the potential for personal contact such as wrestling, football, basketball, etc.
  • Incarceration
  • MSM
  • Crowding with poor hygiene

It is important to note that risk factors associated with CA-MRSA are not well defined and infections have occurred among previously healthy persons with no identifiable factors. Said-Salim B, Mathem B, Kreiswirth BM. Community-acquired methicillin Staphylococcus aureus: an emerging pathogen. Infection Control Hospital Epidemiology (6): 451-5.

Clinical characteristics

May present as any of the following skin infections:

  • Boils, abscesses, furuncles, folliculitus cellulitis.
  • May have the appearance of a spider bite.
  • Cutaneous lesions 5 cm or larger in diameter are not uncommon for this infection.
  • Pain and erythema that seem out of proportion to the severity of the cutaneous findings.
  • Necrosis is a strong indicator of infection with CA-MRSA

A more extensive archive of photos may be viewed at: This is MRSA (Methicillin-Resistant Staphylococcus aureus) (March 15, 2004)

Other presentations
  • With progression contiguous bone infection may occur
  • Necrotizing pneumonia both children and adults
  • Bacteremia
  • Although few cases are life threatening, death has been reported


  • Incision & drainage (I&D) of the abscess. Culture the contents of the abscess.
  • If I&D is not performed consider culture of draining wounds or aspirate or biopsy of central area of inflammation.
  • Culture exudates from infected site for positive identification of the organism and antibiotic susceptibilities.

Most CA-MRSA strains are resistant to erythromycin. In the laboratory, CA-MRSA erythromycin-sensitive strains sometimes exhibit inducible resistance to Clindamycin, but this agent continues to work well in most clinical situations. Most CA-MRSA isolates remain susceptible to ciprofloxacin, but data are limited for other fluoroquinolones. More than 95% of CA-MRSA isolates are sensitive to Trimethoprim-sulfamethoxazole (TMP-SMX)

Treatment for outpatient CA-MRSA

Expert consensus recommendations are not yet available; these are interim guidelines only

Definitive Therapy (culture results known, antibiotic susceptibilities known) Options may include

  • TMP-SMX (Septra)
  • Doxycycline
  • Clindamycin (isolates resistant to erythromycin and sensitive to clindamycin should be evaluated for inducible clindamycin resistant, use the "D" test)
  • Linezolid (outpatient use is generally not recommended due to high cost, inducing antimicrobial resistance and toxicity issues.)
  • Rifampin may be added to any of the above regimens but should never be used alone due to risk of developing resistance.

Note: Before treating, clinicians should consult complete drug information in the manufacturer's package insert or the PDR.

Link to Table.1 Interim Guidelines for Empiric Oral Antimicrobial treatment for outpatients with suspected MRSA Skin and Soft Tissue Infection

Drain abscesses

First-time solitary abscesses < 5 cm can initially be treated with I&D and good skin care only, pending culture results. If positive for CA-MRSA, treat with appropriate antibiotics.

Patients should be instructed as follows:

  • Wash whole body (scalp to toes) daily for 5 days with Chlorhexidine (Hibliclens) antiseptic soap
  • If artificial nails or fingernail polish in use advise pt that treatment success improves without these present
  • Scrub fingernails for one minute with nail brush twice daily
  • Keep wounds that are draining or have exudates covered with clean dry bandages. Bandages or tape can be discarded with the regular trash.
  • Patient family and others in close contact should wash their hands frequently with soap and warm water or use an alcohol-based hand sanitizer, especially after changing soiled bandages or touching the infected wound.
  • Avoid sharing personal items such as towels, washcloths, razors, clothing or uniforms that may have had contact with the infected wound or bandage. Wash sheets, towels and clothes that become soiled with hot water (>160 F for at least 25") and laundry detergent. Dry clothes in a hot dryer.
  • Disinfect all non-clothing (and non-disposable items that come in contact with the wound or wound drainage) with a solution of 1 tablespoon of household bleach mixed in one quart of water prepared fresh each day or a store bought household disinfectant
  • Avoid participating in contact sports or other skin-to-skin activities until the infection has healed.

The Los Angeles County Department of Health Services has developed strategies for reducing transmission of CAMRSA in Non-Healthcare Settings this guide may be accessed at

Eradication of MRSA colonization (decolonization)

There is no consensus regarding treatment to eradicate MRSA colonization. In general, decolonization is not routinely recommended*

Circumstances in which it may seem prudent to consider decolonization are:

  1. Patients with recurrent MRSA infections despite appropriate treatment
  2. Ongoing MRSA transmission in a well-defined cohort with ongoing contact

*Cochrane Database Syst Rev. 2003;(4)CD003340 Antimicrobial drugs for treating methicillin-resistant Staphylococcus aureus colonization. Loeb M, Main C, Walker-Dilks C, Eady A.

Additional Clinician information about MRSA is available at:


Special thanks to Los Angeles County Department of Health Services and Washington State Department of Health for much of the information contained in this website.

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