> Table of Contents > Methicillin-Resistant Staphylococcus Aureus (MRSA) Skin Infections
Methicillin-Resistant Staphylococcus Aureus (MRSA) Skin Infections
Stephen A. Martin, MD, EdM
Paul P. Belliveau, PharmD, RPh
image BASICS
DESCRIPTION
  • Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) has unique properties allowing 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).
  • The prevalence of CA-MRSA is rapidly increasing in the United States.
  • CA-MRSA typically causes mild to moderate SSTIs, particularly abscesses, furuncles, and carbuncles:
    • Severe or invasive disease from CA-MRSA is less frequent but can include the following:
      • Necrotizing pneumonia with abscesses
      • Necrotizing fasciitis
      • Septic thrombophlebitis
      • Sepsis
      • Osteomyelitis
  • Although less frequent, HA-MRSA can still cause SSTIs in the community. One study showed no significant difference in hospitalization rates among CA-MRSA, HA-MRSA, and methicillin-sensitive S. aureus (MSSA) infections.
  • System(s) affected: skin, soft tissue
EPIDEMIOLOGY
  • Predominant age: all ages, generally younger
  • Predominant sex: female > male
Incidence
  • 316/100,000/year (2004 to 2005)
  • 46/100,000/year pediatric MRSA SSTI hospitalizations (2009)
Prevalence
  • Significantly affected by local epidemiology
  • 25-30% of U.S. population are 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%). In 1993, 1.5 million SSTIs were seen in U.S. emergency rooms. In 2005, this had increased to 3.4 million. Hospital admissions for SSTIs increased 29% between 2000 and 2004.
  • CA-MRSA accounts for up to 75% of all community staphylococcal infections in children.
ETIOLOGY AND PATHOPHYSIOLOGY
  • First noted in 1980. Current U.S. CA-MRSA epidemic began in 1999. The United States 300 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-resistance gene mecA)
RISK FACTORS
  • ˜50% of patients with CA-MRSA do not have an obvious risk factor
  • Use of any antibiotic in the past month.
  • Presence of an abscess
  • Reported “spider bite”
  • History of MRSA infection
  • Close contact with a similar infection
  • Children, particularly in daycare centers
  • Competitive athletes
  • Incarceration
  • Hospitalization in the past 12 months (although S. aureus can colonize for years)
GENERAL PREVENTION
  • Colonization (particularly of the anterior nares) is a risk factor for subsequent S. aureus infection. It is not clear whether this is the case for CA-MRSA. Oropharyngeal and inguinal colonization are equally prevalent.
  • CA-MRSA may be transmitted more easily through environmental and household contact (1)[B].
  • Health care workers are a primary MRSA vector for hospitalized patients, reinforcing the need for meticulous cleaning of hands and equipment.
  • Research for a vaccine is underway.
  • CDC guidance for prevention of MRSA in athletes: http://www.cdc.gov/mrsa/community/team-hc-providers/advice-for-athletes.html
COMMONLY ASSOCIATED CONDITIONS
Many patients are otherwise healthy.
image DIAGNOSIS
PHYSICAL EXAM
  • Furuncles and/or carbuncles, sometimes with surrounding cellulitis. A nonsuppurative cellulitis is also possible, although it is a less common presentation of CA-MRSA.
  • Erythema, warmth, tenderness, swelling
  • Fluctuance
  • Folliculitis, pustular lesions
  • Appearance like an insect or spider bite
  • Tissue necrosis
DIFFERENTIAL DIAGNOSIS
SSTIs due to another cause
DIAGNOSTIC TESTS & INTERPRETATION
Initial Tests (lab, imaging)
  • Wound cultures establish definitive diagnosis. Recent guidelines recommend cultures only when a purulent lesion is accompanied by systemic signs of illness or immunocompromise (2)[B].
  • Susceptibility testing; many labs use oxacillin instead of methicillin.
  • A “D-zone disk-diffusion test” evaluates for inducible clindamycin resistance in CA-MRSA resistant to erythromycin.
  • In unclear cases, ultrasound may help identify abscesses (3,4)[A].
  • Although CT or MRI may show fascial plane edema in necrotizing fasciitis, do not delay surgical intervention waiting for imaging, particularly in ill patients.
Diagnostic Procedures/Other
Purulent lesions should be incised and drained (I&D); needle aspiration is not recommended (2).
image TREATMENT
  • Recent guidelines recommends treating with antibiotics active against MRSA for patients with carbuncles or abscesses who failed initial antibiotic treatment, have markedly impaired host defenses, or present with systemic inflammatory response (SIRS) and hypotension (2).
  • Routine use of agents to eliminate MRSA colonization for patients with active infection or their close contacts is not currently recommended.
  • Most CA-MRSA infections are localized SSTIs and not requiring hospitalization or vancomycin.
  • Initial empirical antibiotic coverage should be based on local CA-MRSA prevalence and individual patient risk factors.
  • http://www.cdc.gov/mrsa/pdf/Flowchart_pstr.pdf
GENERAL MEASURES
  • Modify therapy based on culture and susceptibility.
  • Determine if household or other close contacts have SSTI or other infections and evaluate accordingly.
  • Treat underlying condition (e.g., tinea pedis).
  • Restrict contact if wound cannot be covered.
  • Elevate affected area.
MEDICATION
  • Successful I&D may have more impact than antibiotics in mild cases for both adults and children.
  • Moist heat may work for small furuncles.
  • Patients with an abscess are frequently cured by incision and drainage alone.
  • Packing does not appear to improve outcomes (3)[A].
First Line
CA-MRSA SSTIs: 7- to 14-day course (depends on severity and clinical response):
  • Trimethoprim/sulfamethoxazole (TMP-SMX): DS (160 mg TMP and 800 mg of SMX) 1 to 2 tablet(s) PO BID daily (8 to 12 mg/kg/day of trimethoprim component in 2 divided doses for children)
  • Doxycycline or minocycline: 100 mg PO BID (children >8 years and <45 kg; 2 to 5 mg/kg/day PO in 1 to 2 divided doses, not to exceed 200 mg/day; children >8 years and >45 kg, use adult dosing), taken with a full glass of water
  • P.673

  • Clindamycin: 300 to 450 mg PO QID (30 to 40 mg/kg/day PO in 3 divided doses for children), taken with full glass of water. Check D-zone test in erythromycin-resistant, clindamycin-susceptible S. aureus isolates (a positive test indicates induced resistance—choose a differnt antibiotic).
  • CA-MRSA is resistant to &bgr;-lactams (including oral cephalosporins and antistaphylococcal penicillins) and often macrolides, azalides, and quinolones.
  • Although most CA-MRSA isolates are susceptible to rifampin, this drug should never be used as a single agent because of concerns regarding resistance. The role of combination therapy with rifampin in CA-MRSA SSTIs is not clearly defined.
  • There has been increasing resistance to clindamycin, both initial (˜33%) and induced.
  • Although CA-MRSA isolates are susceptible to vancomycin, oral vancomycin cannot be used for CA-MRSA SSTIs due to limited absorption.
Second Line
Treat severe CA-MRSA SSTIs requiring hospitalization and HA-MRSA SSTIs using:
  • Vancomycin: Generally, 1 g IV q12h (30 mg/kg/day IV in 2 divided doses; in children: 40 mg/kg/day IV in 4 divided doses) vancomycin-like antibiotics that require only 1 or 2 doses may soon be more broadly available (5)[A].
  • Linezolid: 600 mg IV/PO BID uncomplicated: children <5 years of age, 30 mg/kg/day in 3 divided doses; 20 mg/kg/day IV/PO in 2 divided doses for children 5 to 11 years of age; children >11 years, use adult dosing. Complicated: birth to 11 years, 30 mg/kg/day IV/PO in 3 divided doses; older, use adult dosing)
    • Linezolid seems to be more effective than vancomycin for treating people with SSTIs, but current studies have high risk of bias.
  • Clindamycin: 600 mg IV TID; in children, 10 to 13 mg/kg/dose q6-8h up to 40 mg/kg/day
  • Daptomycin: 4 mg/kg/day IV (safety/efficacy not established in patients <18 years of age) if no pulmonary involvement
  • Ceftaroline 600 mg BID IV (for adults)
Pediatric Considerations
  • Tetracyclines not recommended <8 years of age
  • TMP-SMX not recommended <2 months
Pregnancy Considerations
  • Tetracyclines are contraindicated.
  • TMP-SMX not recommended in 1st or 3rd trimester
Geriatric Considerations
A recent review notes no prospective trials in this age group and recommends use of general adult guidelines.
ISSUES FOR REFERRAL
Consider consultation with infectious disease in cases of
  • Refractory CA-MRSA infection
  • Plan to attempt decolonization
SURGERY/OTHER PROCEDURES
Progression to serious SSTIs, including necrotizing fasciitis, is possible and mandates prompt surgical evaluation.
INPATIENT CONSIDERATIONS
Admission Criteria/Initial Stabilization
Consider admission if:
  • Systemically ill (e.g., febrile) with stable comorbidities
  • Systemically well with comorbidities that may delay or complicate resolution of SSTI
  • Presence of SSTI complications (sepsis, necrotizing fasciitis) and comorbidities
  • If indicated, alternatives to inpatient admission include observation units and outpatient parenteral antimicrobial therapy (OPAT) programs
Nursing
Contact precautions
Discharge Criteria
If admitted for IV therapy, assess the following before discharge:
  • Afebrile for 24 hours
  • Clinically improved
  • Able to take oral medication
  • Has adequate social support and is available for outpatient follow-up
image ONGOING CARE
FOLLOW-UP RECOMMENDATIONS
Patient Monitoring
For outpatients:
  • Return promptly with systemic symptoms, worsening local symptoms, or failure to improve within 48 hours. Consider a follow-up within 48 hours of initial visit to assess response and review culture.
PATIENT EDUCATION
  • Keep wounds that are draining covered with clean, dry bandages.
  • Clean hands regularly with soap and water or alcohol-based gel. Hot soapy shower daily.
  • Do not share items that may be contaminated (including razors or towels).
  • Clean clothes, towels, and bed linens
  • National MRSA Education Initiative: www.cdc.gov/mrsa/
  • A mixture of 1/4-cup household bleach diluted in 1 gallon of water can be used to clean surfaces.
PROGNOSIS
In outpatients, improvement should occur within 48 hours.
REFERENCES
1. Uhlemann AC, Dordel J, Knox JR, et al. Molecular tracing of the emergence, diversification, and transmission of S. aureus sequence type 8 in a New York community. Proc Natl Acad Sci U S A. 2014;111(18):6738-6743.
2. Stevens DL, Bisno AL, Chambers HF, et al. Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update by the Infectious Diseases Society of America. Clin Infect Dis. 2014;59(2):e10-e52.
3. Mistry RD. Skin and soft tissue infections. Pediatr Clin North Am. 2013;60(5):1063-1082.
4. Singer AJ, Talan DA. Management of skin abscesses in the era of methicillin-resistant Staphylococcus aureus. N Engl J Med. 2014;370(11):1039-1047.
5. Chambers HF. Pharmacology and the treatment of complicated skin and skin-structure infections. N Engl J Med. 2014;370(23):2238-2239.
Additional Reading
&NA;
  • Amin AN, Cerceo EA, Deitelzweig SB, et al. Hospitalist perspective on the treatment of skin and soft tissue infections. Mayo Clin Proc. 2014;89(10):1436-1451.
  • Chen LF, Chastain C, Anderson DJ. Communityacquired methicillin-resistant Staphylococcus aureus skin and soft tissue infections: management and prevention. Curr Infect Dis Rep. 2011;13(5):442-450.
  • Fenster DB, Renny MH, Ng C, et al. Scratching the surface: a review of skin and soft tissue infections in children. Curr Opin Pediatr. 2015;27(3):303-307.
  • Fitch MT, Manthey DE, McGinnis HD, et al. Videos in clinical medicine. Abscess incision and drainage. N Engl J Med. 2007;357(19):e20.
  • Gurusamy KS, Koti R, Toon CD, et al. Antibiotic therapy for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections in surgical wounds. Cochrane Database Syst Rev. 2013;(8):CD009726.
  • Holmes NE, Howden BP. What's new in the treatment of serious MRSA infection? Curr Opin Infect Dis. 2014;27(6):471-478.
  • Ramakrishnan K, Salinas RC, Agudelo Higuita NI. Skin and soft tissue infections. Am Fam Physician. 2015;92(6):474-483.
Codes
&NA;
ICD10
  • A49.02 Methicillin resis staph infection, unsp site
  • A41.02 Sepsis due to Methicillin resistant Staphylococcus aureus
  • J15.212 Pneumonia due to Methicillin resistant Staphylococcus aureus
Clinical Pearls
&NA;
  • Incise and drain purulent lesions and send for wound culture if abscess is present.
  • Local susceptibility patterns of CA-MRSA dictate antibiotic treatment. The CDC has a helpful algorithm for outpatient treatment of CA-MRSA: http://www.cdc.gov/mrsa/pdf/Flowchart_pstr.pdf
  • CA-MRSA skin lesions are commonly misidentified as “spider bites”.