Can you identify the skin infection from a photograph?

Can Photographs Alone Diagnose Skin Infections?

No, you cannot reliably identify or diagnose a skin infection from a photograph alone—clinical examination, patient history, and often laboratory confirmation are essential for accurate diagnosis and appropriate treatment. 1

Why Photographic Diagnosis is Inadequate

Limited Diagnostic Accuracy

• Even expert clinicians cannot reliably differentiate infection types visually. A study of 15 cornea specialists showed they correctly distinguished bacterial from fungal keratitis by chance in fewer than 70% of cases when viewing photographs of culture-proven infections. 1

• Photographic imaging does not provide substantial diagnostic help for determining infection presence or predicting clinical outcomes in hospital settings, particularly for diabetes-related foot infections. 1

• Infrared or digital thermography similarly fails to offer meaningful diagnostic value for infection assessment based on imaging alone. 1

Critical Information Missing from Photographs

Physical examination findings that photographs cannot capture include: 2

• Pain severity and character—particularly pain disproportionate to visible findings, which is the hallmark of necrotizing soft tissue infection (NSTI) versus simple cellulitis
• Tissue consistency—the hard, wooden feel of subcutaneous tissue extending beyond visible skin involvement
• Crepitus—gas in tissues detectable only by palpation
• Depth of involvement—extent of edema or tenderness beyond cutaneous erythema
• Systemic signs—fever, tachycardia, hypotension, altered mental status

Laboratory data essential for diagnosis: 2

• White blood cell count, C-reactive protein (CRP), erythrocyte sedimentation rate (ESR)
• LRINEC score (requires 6 laboratory values) for NSTI risk stratification
• Blood cultures and tissue cultures for pathogen identification

What Actually Constitutes Proper Diagnosis

The Diagnostic Hierarchy

For definitive infection diagnosis, you need: 1

1. Histological and/or cultural evidence from tissue biopsies or sterile body fluid cultures (gold standard)
2. Microscopic examination of tissue samples with appropriate stains (Gram, Grocott's methenamine silver, periodic acid-Schiff)
3. Clinical examination combined with laboratory biomarkers when tissue sampling is not feasible

When Clinical Examination is Equivocal

If physical findings are diagnostically uncertain: 1

• Assess inflammatory serum biomarkers (CRP, ESR, or procalcitonin)
• Obtain appropriate imaging (CT with IV contrast for suspected deep infections, MRI for CNS/sinus involvement)
• Perform tissue sampling for culture and sensitivity testing

Specific Infection Scenarios

For suspected necrotizing soft tissue infection: 2, 3

• Surgical exploration remains the gold standard—key findings include swollen gray fascia, brownish exudate, extensive tissue undermining, and planes easily dissected with blunt instruments
• CT with IV contrast shows fascial thickening, lack of fascial enhancement, fat stranding, and gas collections (100% sensitivity, 81% specificity in some studies)
• Never delay surgical consultation for imaging when clinical suspicion is high

For diabetes-related foot infections: 1

• Clinical examination focusing on purulence, erythema >2 cm, warmth, tenderness, induration
• Tissue cultures (not swabs) when infection is severe, chronic, or unresponsive to therapy
• Avoid relying on quantitative bacterial counts (≥10⁵ CFU/gram) as this lacks supporting evidence

For suspected fungal versus bacterial keratitis: 1

• Corneal scraping for Gram stain and culture before initiating therapy
• Look for distinguishing features: fungal ulcers have dry appearance, feathered edges, satellite lesions; bacterial ulcers are typically suppurative
• Confocal microscopy may help but requires technical expertise

Common Pitfalls

Critical errors to avoid: 2

• Most NSTI cases are initially misdiagnosed as cellulitis—maintain high suspicion for rapidly progressive infections
• Interpreting rising leukocytosis (e.g., 12 to 35 × 10³/µL over days) as normal postoperative change rather than progressive infection 4
• Using clinical scoring systems to confirm rather than exclude serious infection—they are better at ruling out than ruling in 2

For wound infections post-cesarean: 4

• Do not use prophylactic antibiotics for sterile seromas—this promotes resistance without benefit
• Subfascial collections >4 cm with infection signs warrant immediate drainage, not observation
• Presence of gas within collections suggests uterine rupture, not isolated abscess