What is the treatment for cellulitis (bacterial skin infection) resulting from a bug bite?

Treatment of Cellulitis from Bug Bites

For cellulitis resulting from a bug bite, the recommended first-line treatment is an antibiotic active against streptococci, such as penicillin, amoxicillin, amoxicillin-clavulanate, dicloxacillin, cephalexin, or clindamycin. 1

Antibiotic Selection

• For typical non-purulent cellulitis without systemic signs of infection, use an antibiotic active against streptococci (the most common causative organism) 1

• Suitable oral antibiotics for most patients include:

  • Penicillin
  • Amoxicillin
  • Amoxicillin-clavulanate
  • Dicloxacillin
  • Cephalexin
  • Clindamycin 1

• Consider MRSA coverage if the cellulitis is associated with:

  • Penetrating trauma (including bug bites)
  • Evidence of MRSA infection elsewhere
  • Nasal colonization with MRSA
  • Injection drug use
  • Purulent drainage
  • Systemic inflammatory response syndrome (SIRS) 1, 2

• For MRSA coverage, options include:

  • Oral therapy: doxycycline, clindamycin, or trimethoprim-sulfamethoxazole
  • Intravenous therapy: vancomycin, daptomycin, linezolid, or telavancin 1

Duration of Treatment

• A 5-day course of antimicrobial therapy is as effective as a 10-day course if clinical improvement has occurred by day 5 1
• Treatment should be extended if the infection has not improved within 5 days 1

Adjunctive Measures

• Elevation of the affected area to hasten improvement by promoting gravity drainage of edema and inflammatory substances 1
• Treatment of predisposing conditions, such as tinea pedis, trauma, or venous eczema 1
• In lower extremity cellulitis, careful examination of interdigital toe spaces to treat fissuring, scaling, or maceration that may harbor pathogens 1

Special Considerations

• Blood cultures are not routinely recommended for typical cases of cellulitis 1

• Blood cultures should be obtained for patients with:

  • Malignancy
  • Severe systemic features (high fever, hypotension)
  • Unusual predisposing factors (immersion injury, animal bites, neutropenia, severe cell-mediated immunodeficiency) 1

• Systemic corticosteroids (e.g., prednisone 40 mg daily for 7 days) could be considered in non-diabetic adult patients with cellulitis to reduce inflammation 1

Treatment Algorithm

1. For mild cellulitis without systemic signs:

   • First-line: Cephalexin 500 mg orally four times daily for 5 days 1
   • If penicillin-allergic: Clindamycin 300-450 mg orally four times daily for 5 days 1

2. For cellulitis with systemic signs or from bug bites (increased risk of MRSA):

   • Consider combination therapy with a beta-lactam (cephalexin) plus either trimethoprim-sulfamethoxazole or doxycycline 2
   • Note: A randomized controlled trial showed that adding trimethoprim-sulfamethoxazole to cephalexin did not improve outcomes in uncomplicated cellulitis 3

3. For severe cellulitis requiring hospitalization:

   • Vancomycin plus either piperacillin-tazobactam or imipenem/meropenem 1

Monitoring and Follow-up

• Patients should show clinical improvement within 24-48 hours of starting appropriate antibiotics 4
• Consider outpatient treatment for patients without SIRS, altered mental status, or hemodynamic instability 1
• Hospitalization is recommended if there is concern for deeper or necrotizing infection, poor adherence to therapy, severe immunocompromise, or if outpatient treatment is failing 1

Pitfalls and Caveats

• MRSA is an unusual cause of typical cellulitis, with one study showing that treatment with beta-lactams was successful in 96% of patients 1
• However, bug bites represent a form of penetrating trauma, which increases the risk of S. aureus infection, including MRSA 2
• The term "cellulitis" is not appropriate for cutaneous inflammation associated with collections of pus, such as septic bursitis, furuncles, or skin abscesses 1
• In areas with high prevalence of community-associated MRSA, antibiotics with activity against MRSA (trimethoprim-sulfamethoxazole, clindamycin) may be preferred as empiric therapy 5