Residency · Residency · Medicine Pediatrics
Skin and Soft Tissue Infections: MRSA and Beyond
Overview
Skin and soft tissue infections (SSTIs) are among the most common infections managed in both pediatric and adult emergency departments and outpatient settings. Community-acquired MRSA (CA-MRSA) has dramatically changed the epidemiology and management of SSTIs over the past two decades. SSTIs range from simple impetigo to life-threatening necrotizing fasciitis. Management approach: distinguish purulent from non-purulent infections, assess severity, and determine the need for incision and drainage versus antibiotics alone.
Classification
Non-Purulent SSTIs
Impetigo: superficial, honey-crusted lesions (non-bullous) or bullous vesicles; S. aureus predominant; Group A Streptococcus (GAS) also common. Erysipelas: well-demarcated, raised, bright red plaque with sharp borders; involves upper dermis and lymphatics; predominantly GAS. Cellulitis: poorly demarcated erythema with warmth, swelling, tenderness; involves deeper dermis and subcutaneous tissue; GAS and S. aureus most common. Necrotizing fasciitis: rapidly progressive, deep infection along fascial planes; surgical emergency.
Purulent SSTIs
Folliculitis: superficial infection of hair follicles; S. aureus; "hot tub folliculitis" is Pseudomonas. Furuncle (boil): deeper infection of hair follicle extending into dermis; S. aureus. Carbuncle: coalescence of multiple furuncles; larger and deeper. Abscess: walled-off collection of pus in dermis/subcutaneous tissue; S. aureus (CA-MRSA is predominant in many communities)
<image>Clinical photographs showing the spectrum of SSTIs from superficial impetigo through cellulitis, abscess, and necrotizing fasciitis with key distinguishing features labeled</image>
Community-Acquired MRSA (CA-MRSA)
Epidemiology
USA300 strain predominates in North America. Now the most common cause of purulent SSTIs in many communities (>50% of skin abscesses in EDs) Risk factors: close contact (household members, athletes, military, daycare), incarceration, IV drug use; however, many cases occur without identifiable risk factors. Children and young adults are disproportionately affected.
Microbiology
CA-MRSA differs from healthcare-associated MRSA (HA-MRSA): CA-MRSA: typically susceptible to TMP-SMX, clindamycin, doxycycline; resistant to beta-lactams; carries PVL (Panton-Valentine leukocidin) toxin. HA-MRSA: often multiply resistant; less likely PVL-positive. PVL is a pore-forming toxin associated with skin abscesses and necrotizing pneumonia.
Decolonization
Consider for patients with recurrent MRSA SSTIs and their household contacts. Protocol: mupirocin 2% nasal ointment BID x 5 days + chlorhexidine body wash daily x 5 days. Launder towels, linens; do not share personal hygiene items. Evidence supports reduced recurrence in individuals but mixed results for household decolonization.
Management of SSTIs
Impetigo
Limited disease: topical mupirocin or retapamulin. Extensive disease: oral antibiotics (cephalexin for MSSA; TMP-SMX or clindamycin if MRSA suspected) Hygiene measures: handwashing, avoid sharing towels, keep lesions covered.
Cellulitis (Non-Purulent)
Mild (no systemic symptoms): oral antibiotics targeting streptococci and MSSA. Cephalexin 500 mg QID (adults) or 25-50 mg/kg/day divided QID (children) If penicillin-allergic: clindamycin. Moderate (systemic symptoms, immunocompromised): IV cefazolin, clindamycin, or vancomycin (if MRSA suspected) Severe (sepsis, failed outpatient therapy, rapid progression): IV vancomycin + piperacillin-tazobactam; evaluate for necrotizing infection. MRSA coverage for cellulitis WITHOUT purulence is not routinely recommended unless risk factors present. Mark borders with skin marker to track progression. Duration: 5-7 days, extending if not improving.
Abscess Management
Incision and drainage (I&D): the PRIMARY treatment for cutaneous abscesses; antibiotics are adjunctive. Technique: local anesthesia, incision over point of maximal fluctuance, probe to break loculations, irrigate, pack loosely (debated — some evidence suggests packing is not beneficial for small abscesses) Antibiotics after I&D — the IDSA 2014 guidelines state: Small abscess in immunocompetent patient: I&D alone may be sufficient. However, subsequent RCTs (Talan 2016) showed TMP-SMX after I&D significantly improved cure rates (~83% vs 69%) and reduced recurrence. Current consensus trending toward adding antibiotics for most abscesses, especially >2 cm.
Antibiotic Selection for MRSA SSTIs
| Agent | Adult Dose | Pediatric Dose | Route | Notes |
|---|---|---|---|---|
| TMP-SMX | 1-2 DS tabs BID | 8-12 mg/kg/day TMP divided BID | Oral | First-line oral for MRSA; poor strep coverage |
| Clindamycin | 300-450 mg TID | 30-40 mg/kg/day divided TID | Oral | Check D-test; anti-toxin properties |
| Doxycycline | 100 mg BID | Avoid in <8 years | Oral | Good MRSA coverage; photosensitivity |
| Vancomycin | AUC/MIC-guided dosing | 15 mg/kg IV q6h | IV | First-line IV for MRSA |
| Daptomycin | 4-6 mg/kg IV daily | Limited pediatric data | IV | Not for pneumonia (inactivated by surfactant) |
| Linezolid | 600 mg BID | 10 mg/kg TID (<12 years) | IV/PO | Monitor for myelosuppression if >14 days |
Oral options: TMP-SMX DS (1-2 tabs BID adults; 8-12 mg/kg/day TMP divided BID children); Clindamycin 300-450 mg TID (adults); 30-40 mg/kg/day divided TID (children) — check D-test for inducible resistance. Doxycycline 100 mg BID (adults; avoid in children <8 years); IV options (severe SSTIs):; Vancomycin (first-line IV for MRSA; monitor trough or AUC/MIC); Daptomycin 4-6 mg/kg IV daily; Linezolid 600 mg BID (adult) / 10 mg/kg TID (children <12); Clindamycin IV.
<image>Treatment algorithm for SSTIs based on IDSA 2014 guidelines showing the purulent versus non-purulent distinction with severity-stratified management including antibiotic selection</image>
Necrotizing Soft Tissue Infections (NSTIs)
Classification
Type I (polymicrobial): mixed aerobic and anaerobic organisms; typically in immunocompromised, diabetics, post-surgical; Fournier gangrene is perineal Type I NSTI. Type II (monomicrobial): GAS most common; can occur in healthy individuals; associated with toxic shock syndrome. Type III: Vibrio vulnificus (saltwater/raw oyster exposure); Aeromonas (freshwater)
Clinical Features
Pain out of proportion to examination findings (classic early finding) Rapid progression of erythema, edema, bullae, crepitus (gas in tissues) Systemic toxicity: fever, tachycardia, hypotension. Skin changes: dusky/violaceous discoloration, hemorrhagic bullae, skin necrosis. May progress to frank gangrene and septic shock within hours.
Diagnosis
Clinical diagnosis — do NOT delay surgery for imaging. LRINEC score (Laboratory Risk Indicator for Necrotizing Fasciitis): CRP, WBC, hemoglobin, sodium, creatinine, glucose; score >= 6 suggests NSTI; sensitivity is imperfect — clinical suspicion overrides. CT: fascial thickening, gas tracking along fascial planes, fluid collections; useful when diagnosis uncertain but should not delay surgical consultation. MRI: most sensitive imaging but too slow for acute management.
Management
SURGICAL EMERGENCY: early aggressive surgical debridement is the most important intervention. Return to OR every 24-48 hours for re-exploration and debridement until no further necrotic tissue. Broad-spectrum antibiotics: vancomycin + piperacillin-tazobactam + clindamycin (clindamycin for anti-toxin effect against GAS exotoxins) ICU management: aggressive fluid resuscitation, vasopressors, transfusion. IVIG: controversial adjunct in GAS-associated NSTI with toxic shock syndrome. Mortality remains 20-40% despite aggressive treatment.
Pediatric-Specific Considerations
Periorbital vs. Orbital Cellulitis
Periorbital (preseptal): infection anterior to orbital septum; eyelid edema, erythema; usually from local skin infection or sinusitis; treat with oral antibiotics (amoxicillin-clavulanate); close follow-up. Orbital (postseptal): infection posterior to septum; proptosis, ophthalmoplegia, pain with eye movement, decreased visual acuity; EMERGENCY — CT orbits with contrast; IV antibiotics (ampicillin-sulbactam or ceftriaxone + metronidazole); ophthalmology and ENT consultation; surgical drainage if subperiosteal abscess.
Neonatal Skin Infections
Omphalitis: periumbilical erythema/drainage; risk of rapid systemic spread; IV antibiotics. Staphylococcal scalded skin syndrome (SSSS): S. aureus exfoliative toxin; diffuse tender erythema with skin peeling; differentiate from TEN (skin biopsy shows superficial cleavage in SSSS vs. full-thickness in TEN); treat with IV nafcillin/oxacillin; NO steroids.
Perianal Abscess/Cellulitis
Perianal streptococcal dermatitis: well-demarcated perianal erythema, pain with defecation; GAS; treat with oral penicillin/amoxicillin x 10 days + topical mupirocin. Perianal abscess in infants: may be associated with fistula-in-ano; surgical consultation.
<image>Comparison of periorbital versus orbital cellulitis showing clinical features, CT imaging findings, and management approach for each</image>
Recurrent SSTIs
Evaluation
Culture drainage for susceptibilities; Assess for predisposing factors: obesity, diabetes, eczema, immunodeficiency, injection drug use. MRSA decolonization (described above); Evaluate household contacts for carriage.
Prevention Strategies
Personal hygiene: daily bathing, handwashing, no sharing personal items. Wound care: keep cuts/abrasions clean and covered. Environmental cleaning: disinfect high-touch surfaces. Athletic setting: shower after practice, avoid sharing equipment, cover wounds. Dilute bleach baths (1/4-1/2 cup per full bathtub, 2-3 times/week): helpful for patients with concurrent eczema and recurrent MRSA.
Clinical Pearls
I&D is the most important intervention for an abscess — antibiotics alone are insufficient for collections that need drainage. Bedside ultrasound is valuable for distinguishing cellulitis from abscess when clinical exam is equivocal — saves children from unnecessary I&D or missed drainage. Pain out of proportion in a rapidly progressive SSTI = necrotizing fasciitis until proven otherwise; this is a surgical emergency, not an antibiotic problem. Clindamycin has excellent tissue penetration and anti-toxin properties (inhibits protein synthesis including toxin production by GAS and S. aureus); preferred adjunct in severe SSTIs. TMP-SMX has poor streptococcal coverage — it should not be used as monotherapy for non-purulent cellulitis (which is predominantly streptococcal) Always perform a D-test when clindamycin susceptibility is reported and erythromycin resistance is present — inducible clindamycin resistance is common in MRSA. In recurrent SSTIs, think beyond the skin: evaluate for hidradenitis suppurativa, immunodeficiency (including HIV), and chronic granulomatous disease in children.
References
- Stevens DL, Bisno AL, Chambers HF, et al. Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections: 2014 Update by IDSA. Clin Infect Dis. 2014;59(2):e10-e52.
- Talan DA, Mower WR, Krishnadasan A, et al. Trimethoprim-Sulfamethoxazole versus Placebo for Uncomplicated Skin Abscess. N Engl J Med. 2016;374(9):823-832.
- Liu C, Bayer A, Cosgrove SE, et al. Clinical Practice Guidelines by IDSA for the Treatment of MRSA Infections in Adults and Children. Clin Infect Dis. 2011;52(3):e18-e55.
- Fritz SA, Hogan PG, Hayek G, et al. Household versus Individual Approaches to Eradication of Community-Associated Staphylococcus aureus in Children. Clin Infect Dis. 2012;54(6):743-751.
