Management of Skin and Soft Tissue Infections
Classification Framework
SSTIs must be classified by three key characteristics: necrotizing versus non-necrotizing, anatomical depth, and presence of purulence. 1
Severity Stratification
Severity assessment determines treatment intensity and should be based on systemic inflammatory response criteria:
- Mild (Class 1): No systemic signs, no significant comorbidities 2
- Moderate (Class 2): Presence of SIRS criteria (temperature >38°C or <36°C, heart rate >90 bpm, respiratory rate >24/min, WBC >12,000 or <4,000 cells/μL) OR systemically well with complicating comorbidities 1, 2, 3
- Severe (Class 3-4): Toxic appearance, treatment failure, immunocompromised status, hypotension, or signs of deeper infection (bullae, skin sloughing, disproportionate pain, rapid progression) 1, 2, 3
Infection-Specific Management
1. Impetigo
Pathogen: Staphylococcus aureus and/or β-hemolytic Streptococcus (including increasing CA-MRSA) 1, 4
Treatment:
- Limited lesions: Topical mupirocin or retapamulin ointment twice daily 1
- Extensive lesions: Oral antibiotics
2. Erysipelas
Pathogen: Primarily Streptococcus pyogenes (Group A Streptococcus) 4
Treatment:
- Mild cases: Oral β-lactams (cephalexin 500 mg QID or dicloxacillin 500 mg QID) 1
- Severe cases: IV penicillin or cefazolin 1
3. Cellulitis
Pathogen: Streptococci (diffuse infection) or staphylococci (more localized) 4, 5
Treatment approach by severity:
Mild cellulitis (no systemic signs):
- Oral β-lactams: Cephalexin 500 mg QID or dicloxacillin 500 mg QID 1
- Penicillin-allergic: Clindamycin 300-450 mg QID 1
Moderate cellulitis (SIRS present):
- If MRSA not suspected: Cefazolin 1 g IV every 8 hours 1
- If MRSA suspected: Add vancomycin 30 mg/kg/day divided every 12 hours IV 1
Severe cellulitis (toxic appearance, hypotension, organ dysfunction):
- Vancomycin 30 mg/kg/day IV PLUS piperacillin-tazobactam or carbapenem for polymicrobial coverage 2, 4
4. Abscesses and Furuncles
Pathogen: Staphylococcus aureus (including MRSA) 1, 5
Treatment:
Simple abscesses:
- Incision and drainage is the primary treatment; antibiotics are NOT routinely needed 1, 4
- Add antibiotics ONLY if: systemic signs present, immunocompromised, incomplete source control, or significant surrounding cellulitis (>2 cm) 4
Complex abscesses (perianal, perirectal, injection drug use sites):
- Incision and drainage PLUS broad-spectrum antibiotics covering Gram-positives, Gram-negatives, and anaerobes 4
- Empiric regimen: Vancomycin PLUS piperacillin-tazobactam or carbapenem 2, 4
Carbuncles with treatment failure or SIRS:
- MRSA-active antibiotic required: vancomycin, linezolid, or daptomycin 1
5. Bite Wounds (Animal and Human)
Infection risk: Cat bites 30-50%, dog bites 5-25%, human bites 20-25% 4
Pathogens: Polymicrobial (oral flora, Pasteurella in animals, Eikenella in humans, anaerobes) 4
Treatment:
- Early aggressive surgical debridement PLUS antibiotics 4
- Amoxicillin-clavulanate 875/125 mg BID (first-line oral) 1
- Severe infections: Ampicillin-sulbactam 1.5-3 g IV every 6 hours or piperacillin-tazobactam 4
- Avoid high-pressure irrigation—this drives bacteria deeper into tissue 4
6. Traumatic Wounds
Treatment:
- Irrigation and debridement of necrotic tissue are the most critical interventions 4
- Prophylactic antibiotics NOT routinely recommended 4
- Antibiotics required if: systemic signs, immunocompromised, severe comorbidities, severe/deep wounds, or significant cellulitis 4
- Empiric regimen: Broad-spectrum covering aerobes and anaerobes (amoxicillin-clavulanate or piperacillin-tazobactam) 4
7. Necrotizing Soft Tissue Infections
Clinical red flags requiring immediate surgical consultation:
- Pain disproportionate to physical findings 2
- Violaceous bullae or skin sloughing 2
- Skin anesthesia 2
- Rapid progression 2, 3
- Gas in tissue on imaging 2
Classification:
- Type I: Polymicrobial (mixed aerobes and anaerobes) 4
- Type II: Monomicrobial (Streptococcus pyogenes or MRSA) 4
- Type III: Gas gangrene (Clostridium species) 4
Treatment:
Immediate aggressive surgical debridement is ESSENTIAL—survival depends on it 1, 2, 4
Empiric antibiotic regimen (broad-spectrum polymicrobial coverage):
Gram-positive coverage (including MRSA):
- Vancomycin 30 mg/kg/day IV 2, 4
- OR Linezolid 600 mg IV/PO every 12 hours 2, 4, 6
- OR Daptomycin 4-6 mg/kg IV daily 2, 4
PLUS Gram-negative and anaerobic coverage:
- Piperacillin-tazobactam 3.375-4.5 g IV every 6 hours 2, 4
- OR Carbapenem (imipenem, meropenem, or ertapenem) 2, 4
- OR Ceftriaxone 1-2 g IV daily PLUS metronidazole 500 mg IV every 8 hours 2, 4
- OR Fluoroquinolone PLUS metronidazole 2, 4
For confirmed Group A Streptococcus necrotizing fasciitis:
- Clindamycin 600-900 mg IV every 8 hours PLUS penicillin G 4 million units IV every 4 hours (clindamycin suppresses toxin production) 4
Duration: Continue antibiotics until no further debridement needed, clinical improvement achieved, and afebrile for 48-72 hours 4
8. Diabetic Foot Infections
Pathogen: Often polymicrobial; evaluate for underlying osteomyelitis 2
Treatment:
- Always assess for osteomyelitis with imaging (plain radiographs initially) 2
- Mild infections: Amoxicillin-clavulanate 875/125 mg BID 1
- Moderate-severe infections: Linezolid 600 mg BID OR vancomycin PLUS piperacillin-tazobactam or carbapenem 2, 6
- More aggressive management required than non-diabetic SSTIs 2
Antibiotic Selection by Pathogen
MSSA (Methicillin-Susceptible S. aureus)
Parenteral:
- Nafcillin or oxacillin 1-2 g IV every 4 hours (drug of choice) 1
- Cefazolin 1 g IV every 8 hours (for penicillin allergy, except immediate hypersensitivity) 1
Oral:
MRSA (Methicillin-Resistant S. aureus)
Parenteral:
- Vancomycin 30 mg/kg/day IV divided every 12 hours (drug of choice) 1, 4
- Daptomycin 4-6 mg/kg IV daily 1, 2
- Linezolid 600 mg IV every 12 hours 1, 2
- Ceftaroline 600 mg IV every 12 hours 1
Oral:
- Linezolid 600 mg PO every 12 hours 1, 6
- Clindamycin 300-450 mg QID (if susceptible; check for inducible resistance) 1, 7
- Doxycycline or minocycline 100 mg BID 1
- Trimethoprim-sulfamethoxazole 1-2 double-strength tablets BID 1
Diagnostic Workup
Obtain cultures when:
- Moderate or severe infection 1, 2
- Treatment failure 1
- Immunocompromised host 1
- Systemic signs present 1
Culture methods:
- Needle aspiration, tissue biopsy, or swab of purulent drainage 2
- Blood cultures if bacteremia suspected 2
Imaging:
- Plain radiographs to evaluate for gas, foreign bodies, or osteomyelitis 2
- Consider CT or MRI for deep infections or necrotizing fasciitis 2
Treatment Duration
- Simple SSTIs: 5-7 days (if clinical improvement) 2
- Complicated SSTIs: 7-14 days 2
- Necrotizing infections: Until no further debridement needed and afebrile 48-72 hours 4
- Osteomyelitis: 4-6 weeks minimum 2
Monitoring and Reassessment
Reassess within 24-48 hours to evaluate treatment response 2
Signs of treatment failure requiring escalation:
Consider repeat surgical debridement if no clinical improvement in necrotizing infections 2
Adjust antibiotics based on culture results and clinical response 2
Monitor for complications: bacteremia, osteomyelitis, sepsis 2
Critical Pitfalls to Avoid
- Never delay surgical consultation for suspected necrotizing infections—mortality increases with each hour of delay 1, 2
- Do not use antibiotics alone for abscesses—incision and drainage is mandatory 1, 4
- Avoid high-pressure wound irrigation—it spreads bacteria into deeper tissue planes 4
- Do not assume all cellulitis is streptococcal—MRSA coverage needed if purulence, abscess, or treatment failure 1, 3
- Immunocompromised patients require immediate treatment and broader coverage for atypical organisms 2, 3, 5
- Leukopenia (<4,000 cells/μL) is as concerning as leukocytosis and indicates severe infection 1, 3
- Clindamycin resistance can be inducible in MRSA—perform D-test if using for MRSA 1
- Consider recurrent MRSA decolonization protocols for patients with multiple episodes 2