How do you differentiate and treat bacterial vs fungal rashes?

Differentiating and Treating Bacterial vs Fungal Rashes

Bacterial rashes typically present with purulent exudate, pustules, honey-colored crusting, and rapid progression with surrounding erythema and warmth, while fungal rashes characteristically show peripheral scaling, satellite lesions (for Candida), and lack purulent drainage—making clinical appearance the primary differentiator before culture confirmation. 1, 2, 3

Clinical Differentiation Algorithm

Bacterial Infection Features

• Purulent exudate and pustules are the most reliable clinical indicators distinguishing bacterial infection from inflammatory dermatitis 1
• Honey-colored crusting suggests impetigo caused by Staphylococcus aureus or Streptococcus pyogenes 4
• Rapid progression with increasing pain, warmth, and surrounding inflammation indicates bacterial etiology 2
• Tender, erythematous nodules that may become necrotic suggest deeper bacterial involvement 1

Fungal Infection Features

• Peripheral scaling with central clearing is characteristic of dermatophyte infections 3
• Satellite lesions (small pustules surrounding a primary lesion) are pathognomonic for Candida 3
• Erythematous regions in skin folds without purulent drainage suggest candidal intertrigo 3
• Maculopapular lesions with mixture of hyphae and budding yeast on biopsy indicate fungal etiology 1

Critical Pitfall

Do not delay bacterial culture if any purulent component or honey-crusting is present, as S. aureus colonizes >90% of atopic dermatitis patients but only requires treatment when frank infection is evident 1, 4

Diagnostic Confirmation

When to Culture

• Obtain bacterial culture with antibiotic susceptibility for purulent, honey-crusted lesions or recurrent/non-responsive infections 1, 2, 4
• Perform potassium hydroxide (KOH) preparation for suspected fungal infections showing peripheral scaling or satellite lesions 3
• Consider punch biopsy when diagnosis remains uncertain or severe drug reaction is suspected 5

Wood Lamp Examination

• Use Wood lamp to identify Corynebacterium minutissimum (coral-red fluorescence) in bacterial intertrigo 3

Treatment Approach

Bacterial Infections

Localized/Uncomplicated:

• Apply topical mupirocin 2% ointment for localized impetigo or suspected bacterial infection, which is highly effective against S. aureus and beta-hemolytic streptococci 2, 3
• Use topical mupirocin for secondary streptococcal infections in intertrigo 3

Extensive/Complicated:

• Administer oral antibiotics (cephalexin or dicloxacillin) if extensive disease or systemic symptoms present 4
• For severe infections or immunocompromised patients, use vancomycin plus piperacillin-tazobactam or carbapenem with broad-spectrum coverage including Pseudomonas aeruginosa 1, 2
• Continue treatment for 2 weeks or until complete resolution of skin lesions 1

Critical Caveat: Systemic antibiotics are not recommended for non-infected atopic dermatitis or simple colonization, as bacterial counts return to baseline within days to weeks after discontinuation and may increase antibiotic resistance 1

Fungal Infections

Candidal Infections:

• Treat superficial candidal infections with topical nystatin, clotrimazole, ketoconazole, oxiconazole, or econazole 1, 3
• For resistant cases, use oral fluconazole 100-400 mg daily 1, 3
• For invasive candidiasis in neutropenic patients, use echinocandin (caspofungin, micafungin, or anidulafungin) as first-line therapy 1
• Alternative for Candida parapsilosis: lipid formulation amphotericin B 3-5 mg/kg daily 1
• Continue treatment for 2 weeks after clearance of bloodstream infection or resolution of skin lesions 1

Dermatophyte Infections:

• Apply topical antifungals (clotrimazole, ketoconazole) for localized tinea infections 6, 3
• Use systemic antifungals for extensive or nail involvement 6

Mold Infections (Aspergillus, Fusarium):

• Treat with voriconazole 6 mg/kg IV every 12 hours for 2 doses, then 4 mg/kg IV every 12 hours for Aspergillus or Fusarium species 1
• Alternative: posaconazole 400 mg twice daily with meals 1
• These infections carry high mortality and require aggressive treatment in neutropenic patients 1

Supportive Care Principles

Wound Management

• Cleanse gently with sterile normal saline; avoid iodine or antibiotic solutions unless specifically indicated 2
• Select nonadherent dressings to reduce bacterial superinfection and promote healing 2
• Change dressings when soiled using aseptic technique 2
• Elevate affected area if swollen 2

Prevention of Secondary Infection

• Keep affected area clean and dry between dressing changes 2
• For extensive erosive lesions, cover with appropriate bandages to reduce bacterial superinfection 2

When to Escalate Care

Immediate hospitalization required for:

• Skin sloughing >30% body surface area suggesting Stevens-Johnson syndrome/toxic epidermal necrolysis 5
• Systemic symptoms (fever, hypotension, altered mental status) with spreading infection 2, 7
• Suspected necrotizing fasciitis requiring surgical debridement 1, 7
• Immunocompromised patients with any significant skin infection 1, 2

Specialist consultation needed for:

• Recurrent infections suggesting underlying immunosuppression, diabetes, or vascular insufficiency 2
• Failure to respond to initial therapy within 48-72 hours 2
• Suspected invasive fungal infection in neutropenic patients 1