MRSA Skin Infections- Causes, Symptoms, Diagnosis, Treatment and Ongoing care

Basics

Description

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has properties that allow it to create skin and soft tissue infections (SSTIs) in otherwise healthy hosts: CA-MRSA has a different virulence and disease pattern than hospital-acquired MRSA (HA-MRSA).MRSA infections acquired by persons who have not been recently (<1 year) hospitalized or had a medical procedure (e.g., dialysis, surgery, catheters) are known as CA-MRSA infections: This definition is evolving, given the increasing intersection of HA- and CA-MRSA.The prevalence of CA-MRSA is rapidly increasing in the US.CA-MRSA typically causes mild-to-moderate SSTIs, particularly abscesses, furuncles, and carbuncles: Severe disease from CA-MRSA is less frequent, but can include: In 1 review, 77% of CA-MRSA infections were SSTIs; only 6% of infections were invasive (e.g., bacteremia, osteomyelitis).Although less frequent, HA-MRSA can still cause SSTIs in the community, and clinicians should be alert to this possibility. 1 study showed no significant difference in hospitalization rates among CA-MRSA, HA-MRSA, and methicillin-sensitive Staphylococcus aureus (MSSA).System(s) affected: Skin; Soft tissue

Epidemiology

Predominant age: All ages, generally youngerPredominant sex: Female > Male

Incidence

18.0–26/100,000/year (2001–02)155/100,000/year (2004) in higher risk setting

Prevalence

Still significantly affected by local epidemiology25–30% of US population is colonized with S. aureus; up to 7% is colonized with MRSA.CA-MRSA was isolated in 59% of skin and soft tissue infections presenting to 11 emergency departments (range 15–74%). In 1993, 1.5 million SSTIs were seen in US emergency rooms (ERs). In 2005, this had increased to 3.4 million. Hospital admission data indicate a 29% increase in SSTIs from 2000–2004.CA-MRSA accounts for up to 75% of all community staphylococcal infections in children.

Risk Factors

Although several factors are associated with CA-MRSA, their presence or absence cannot reliably predict CA-MRSA itself; in 1 study, almost 1/2 the patients with CA-MRSA had no established risk factor.Any antibiotic use in past monthPresence of an abscessReported “spider bite”History of MRSA infectionClose contact with a similar infectionChildren, particularly in day care centersCompetitive athletesIncarcerationHigh prevalence in the communityHospitalization in the past 12 months (although S. aureus can remain colonized for years)

General Prevention

Prior research has established colonization (particularly of the anterior nares) as a risk factor for subsequent S. aureus infection. It is not yet clear whether this is also the case for CA-MRSA. Recent work has indicated that rectal colonization may be more significant.CA-MRSA may be transmitted much more through the environment, including households, than via nares colonization.Health care workers have been found to be a major vector of MRSA for hospitalized patients, reinforcing the need for aggressive cleaning of hands and common equipment.Research for a vaccine is underway.

Etiology

First noted in 1980, CA-MRSA’s current US epidemic began in 1999. The USA 300 clone is predominant.CA-MRSA is currently distinguished from HA-MRSA by: Lack of a multidrug-resistant phenotypePresence of exotoxin virulence factorsType IV staphylococcus cassette cartridge (contains the methicillin-resistance gene mecA)

Commonly Associated Conditions

Many patients are otherwise healthy.

Diagnosis

History

Potential risk factorsComplaint of “spider bite”Prior MRSA skin infectionRisk factors alone cannot rule in or rule out a CA-MRSA infection (1)[B].

Physical Exam

Exam consistent with a furuncle/carbuncle (boils) or abscess, sometimes with a surrounding cellulitis. An isolated cellulitis is also possible, although it is a less common presentation of CA-MRSA. A recent study, however, shows S. aureus to be a causal agent in half of cellulitis cases.ErythemaIncreased warmthTendernessSwellingFluctuanceInfected woundFolliculitis, pustular lesionsAppearance like an insect or spider biteTissue necrosis

Diagnostic Tests & Interpretation

Lab

Initial lab tests

Wound cultures are essential for diagnosis.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 (2)[C].

Imaging

Initial approach

In unclear cases, ultrasound may help delineate an abscess.Although computed tomography or magnetic resonance imaging may show fascial plane edema in necrotizing fasciitis, they should not delay intervention.

Diagnostic Procedures/Surgery

Purulent lesions should be incised and drained (I & D), cultured, and tested for susceptibilities.

Differential Diagnosis

Skin and soft tissue infections due to another cause

Treatment

Evidence for the treatment of CA-MRSA SSTIs, including oral antibiotics, has not been systematically evaluated in randomized controlled trials. Although investigations are increasing, current recommendations are generally based on results of small case series, anecdotal reports, and anticipated susceptibility profiles.Systematic review does not recommend agents to eliminate MRSA colonization for patients with infection or their close contacts (3)[C].Most CA-MRSA infections are localized SSTIs and do not require hospitalization or vancomycin therapy (3)[C].Initial empirical antibiotic coverage should be based on local CA-MRSA prevalence and individual patient risk factors. In one pediatric model, cephalexin was the optimal antibiotic for an SSTI only when CA-MRSA prevalence was <10%.

Medication

Alert

For purulent infections, basic principles include surgical drainage and debulking, wound culture, and narrow-spectrum antimicrobials: Successful I & D may have more of an effect than antibiotics in mild cases for both adults and children, and is important in general.Moist heat may work for small furuncles.Patients with an abscess are frequently cured by drainage alone.CA-MRSA is resistant to ß-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 for rapid emergence of resistance. The role of combination therapy with rifampin in CA-MRSA SSTIs is still 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 gastrointestinal absorption.

First Line

CA-MRSA SSTIs: Treat with a 7–14-day course of 1 of the following agents (duration of therapy depends on severity and clinical response):

Trimethoprim/sulfamethoxazole: DS (160 mg TMP and 800 mg of SMX) 1–2 tablet(s) p.o. b.i.d. daily (8–12 mg/kg/d of trimethoprim component in 2 divided doses for children)Doxycycline or minocycline: 100 mg p.o. b.i.d. (children >8 years and <45 kg; 2–5 mg/kg/d p.o. in 1–2 divided doses, not to exceed 200 mg/d; children >8 years and >45 kg: use adult dosing), taken with a full glass of waterClindamycin: 300–600 mg p.o. t.i.d. (10–20 mg/kg/d p.o. in 3 divided doses for children), taken with full glass of water. Check D-zone test in erythromycin-resistant, clindamycin-susceptible S. aureus isolates (test is positive with induced resistance).

Second Line

The above medication options are not sufficient for treatment of severe CA-MRSA SSTIs requiring hospitalization or for HA-MRSA SSTIs. For such infections, consider 1 of the following (4)[A]:

Vancomycin: Generally 1 g IV q12h (30 mg/kg/d IV in 2 divided doses; in children: 40 mg/kg/d IV in 4 divided doses)Linezolid: 600 mg IV/p.o. b.i.d. (Uncomplicated: children <5 years of age, 30 mg/kg/d in 3 divided doses; 20 mg/kg/d IV/p.o. in 2 divided doses for children 5–11 years of age; children >11 years, use adult dosing. Complicated: birth–11 years, 30 mg/kg/d IV/p.o. in 3 divided doses; older, use adult dosing)Daptomycin: 4 mg/kg/d IV (safety/efficacy not established in patients <18 years of age) if no pulmonary involvementTigecycline: 100 mg IV once, then 50 mg IV every 12 hours (for adults)

Pediatric Considerations

Tetracyclines not recommended <8 yearsTMP-SMX not recommended <2 months

Pregnancy Considerations

Tetracyclines are contraindicated.TMP-SMX not recommended in 3rd trimester

Additional Treatment

General Measures

Modify therapy as necessary based on culture and susceptibility testing.Determine if household or other close contacts have SSTI or other infections, and facilitate evaluation.Treat underlying condition (e.g., tinea pedis).Restrict contact if wound cannot be covered.Elevate affected area.

Issues for Referral

In addition to inpatient concerns, consider consultation with an infectious disease specialist in cases of:

Refractory CA-MRSA infectionPlan to attempt decolonization

Surgery/Other Procedures

Progression to serious SSTIs, including necrotizing fasciitis, is possible and mandates prompt surgical evaluation.

In-Patient Considerations

Initial Stabilization

Depends on severity of SSTI, presence of SSTI complications (sepsis, necrotizing fasciitis), and comorbidities

Admission Criteria

Consider admission in patients either:

Systemically ill (e.g., febrile) with stable comorbidities, orSystemically well with comorbidities that may delay or complicate resolution of their SSTI

Nursing

Contact precautions

Discharge Criteria

If admitted for IV therapy:

Afebrile for 24 hoursClinically improvedAble to take oral medicationHas adequate social support and available for outpatient follow-up

Ongoing Care

Follow-Up Recommendations

Patient Monitoring

For outpatients:

Return promptly if patient develops systemic symptoms, worsening local symptoms, or does not 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 shower daily with soap.Do not share items that may be contaminated (including razors or towels).Clean clothes, towels, and bed linens.

Prognosis

In outpatients, improvement should occur within 48 hours.Data are limited as to risk of recurrence.

Complications

Necrotizing pneumonia or empyema (after an influenzalike illness)Necrotizing fasciitisSepsis syndromePyomyositis and osteomyelitisPurpura fulminansDisseminated septic emboliEndocarditis

References

1. Daum RS. Clinical practice. Skin and soft-tissue infections caused by methicillin-resistant Staphylococcus aureus. N Engl J Med. 2007;357:380–90.

2. Moellering RC. A 39-year-old man with a skin infection. JAMA. 2008;299:79–87.

3. Stryjewski ME, Chambers HF. Skin and soft-tissue infections caused by community-acquired methicillin-resistant Staphylococcus aureus. Clin Infect Dis. 2008;46(Suppl 5):S368–77.

4. Stevens DL, Bisno AL, Chambers HF, et al. Practice guidelines for the diagnosis and management of skin and soft-tissue infections. Clin Infect Dis. 2005;41:1373–406.

5. Chuck EA, Frazee BW, Lambert L, et al. The benefit of empiric treatment for methicillin-resistant Staphylococcus aureus. J Emerg Med. 2010;38:567–71.

Additional Reading

Breen JO et al. Skin and soft tissue infections in immunocompetent patients. Am Fam Physician. 2010;81:893–9.

Gorwitz RJ, et al. Strategies for clinical management of MRSA in the community: Summary of an experts’ meeting convened by the Centers for Disease Control and Prevention. 2006. Accessed 7/9/2010 at: http://www.cdc.gov/ncidod/dhqp/pdf/ar/CAMRSA_ExpMtgStrategies.pdf.

The CDC has gathered information for health care professionals, including clinical guides, via the National MRSA Education Initiative (accessed 7/9/2010) at http://www.cdc.gov/mrsa/. These include a treatment algorithim: http://www.cdc.gov/mrsa/mrsa_initiative/skin_infection/mrsa_algorithm.html. Updated Infectious Disease Society of America guidelines on MRSA are expected in the Fall of 2010 and on skin and sof tissue infections in the Winter of 2011.

Codes

ICD9

041.12 Methicillin resistant Staphylococcus aureusV02.54 Carrier or suspected carrier of Methicillin resistant Staphylococcus aureusV09.0 Infection with microorganisms resistant to penicillins686.8 Other specified local infections of skin and subcutaneous tissue

Snomed

266096002 Methicillin resistant Staphylococcus aureus infection (disorder)19824006 infection of skin AND/OR subcutaneous tissue (disorder)432415000 methicillin resistant staphylococcus aureus carrier (finding)

Clinical Pearls

Incise and drain purulent lesions and send for wound culture.Know the prevalence and susceptibilities of CA-MRSA in your location. Consider use of an algorithm to help guide clinical decisions (5)[B].Use 1/4 cup household bleach diluted in 1 gallon of water to clean surfaces; no evidence that widespread cleaning (with sprays/foggers) works any better than focused cleaning of frequently touched areas.