What is the diagnosis of a skin infection involving fat folds with diffuse erythema and multiple pustules?

Diagnosis: Intertrigo with Secondary Bacterial Infection

The diagnosis is intertrigo (intertriginous dermatitis) with secondary bacterial infection, most likely caused by Staphylococcus aureus or Streptococcus pyogenes, given the presentation of diffuse erythema and multiple pustules in fat folds.

Clinical Presentation and Pathophysiology

Intertrigo is a superficial inflammatory dermatitis occurring on two closely opposed skin surfaces resulting from moisture, friction, and lack of ventilation 1. The condition manifests as:

• Regions of erythema with peripheral scaling in skin folds 1
• Pustules indicating secondary bacterial superinfection 2
• Common locations include axillae, inframammary areas, groin, intergluteal folds, and abdominal pannus 3, 4

The presence of purulent exudate and pustules strongly suggests secondary bacterial infection rather than simple inflammation 2. Excessive friction and inflammation create skin breakdown, providing an entry point for bacterial pathogens 1.

Key Diagnostic Differentiators

Bacterial Intertrigo vs. Candidal Intertrigo

• Candidal intertrigo presents with characteristic satellite lesions (small pustules surrounding the main erythematous area) 1, 5
• Bacterial intertrigo typically shows diffuse pustules without the classic satellite pattern 1
• Candidal infections demonstrate more maceration and less prominent scaling compared to bacterial infections 6

Most Likely Pathogens

• Staphylococcus aureus and Group A beta-hemolytic streptococcus are the primary bacterial causes 1
• Corynebacterium minutissimum (erythrasma) can occur but typically lacks pustules 4
• Pseudomonas aeruginosa should be considered if greenish-blue staining of underclothing is present 7

Diagnostic Confirmation

Clinical diagnosis is typically sufficient, but confirmatory testing may include:

• Bacterial culture from pustule contents to identify the pathogen and guide antibiotic selection 1, 3
• KOH preparation to rule out concurrent fungal infection 1
• Wood lamp examination (coral-red fluorescence suggests Corynebacterium minutissimum) 1, 4

Treatment Approach

For Bacterial Superinfection with Pustules:

Systemic antibiotics are warranted when multiple pustules are present 2:

• First-line oral antibiotics: dicloxacillin, cephalexin, or amoxicillin-clavulanate 8
• If MRSA is suspected (community-acquired, treatment failure, or known colonization): clindamycin or trimethoprim-sulfamethoxazole 8
• Topical mupirocin for localized bacterial infection 1

Adjunctive Measures:

• Minimize moisture and friction with absorptive powders (cornstarch) or barrier creams 3
• Thorough drying of intertriginous areas after bathing 3
• Light, nonconstricting, absorbent clothing; avoid wool and synthetic fibers 3
• Daily changes of undergarments 6

Critical Clinical Pitfalls

Do not confuse this with simple cellulitis 2. The term "cellulitis" is inappropriate for cutaneous inflammation associated with collections of pus such as pustules 2. The distinction is crucial because:

• Primary cellulitis requires antimicrobial therapy alone 2
• Purulent collections (abscesses) require drainage as the primary treatment 2
• Intertrigo with bacterial superinfection requires both antimicrobials AND moisture/friction management 1, 3

Avoid misdiagnosing as atopic dermatitis with secondary infection 2. While both can present with pustules, atopic dermatitis typically has a chronic history with pruritus and eczematous changes, whereas intertrigo is specifically localized to skin folds 2.

When to Escalate Care

Red flags requiring urgent evaluation include 8:

• Worsening fever or systemic toxicity
• Increasing pain or woody-hard feel to subcutaneous tissues (suggesting necrotizing infection)
• Development of bullae or skin necrosis
• Rapid spread beyond the initial skin fold area