What is the most common cause and typical presentation of necrotising fasciitis in children?

Most Common Cause and Presentation of Necrotizing Fasciitis in Children

Streptococcus pyogenes (Group A Streptococcus) is the most common causative organism in pediatric necrotizing fasciitis, particularly following varicella infection or trivial injuries, and children typically present with fever, marked tissue edema with a characteristic peau d'orange appearance, systemic toxicity with altered mental status, and erythema—often without the classic "pain out of proportion" seen in adults. 1, 2, 3, 4

Causative Organisms in Children

Monomicrobial Infections (Type II) - Most Common in Pediatrics

• S. pyogenes dominates as the primary pathogen in monomicrobial pediatric necrotizing fasciitis, especially after varicella lesions or minor trauma like scratches and insect bites 1, 2, 3
• Staphylococcus aureus (including MRSA) and Staphylococcus epidermidis occur less frequently but can coexist with streptococci 1, 2
• Pseudomonas aeruginosa is notably more common in pediatric cases compared to adults and represents an important pathogen unique to this population 3, 5

Polymicrobial Infections (Type I) - Less Common in Children

• Polymicrobial infections involve an average of 5 pathogens per wound, predominantly bowel flora including coliforms and anaerobes 1
• These occur in specific settings: omphalitis, perianal abscesses, penetrating trauma, or injection sites 1, 2

Critical distinction: Monomicrobial (Type 2) fasciitis is much more common in children than polymicrobial (Type 1) fasciitis, which differs from the adult pattern 3

Typical Clinical Presentation in Children

Age Distribution and Anatomic Patterns

• Two distinct frequency peaks: neonates and children aged 1-2 years (predominantly torso involvement), and children around 10 years (predominantly extremities and face) 3
• Mean age across studies is approximately 35-53 months 2, 3
• The abdominal wall is the most common initial site, followed by gluteal region/thigh, head and neck, then extremities 2

Early Clinical Features

• Fever is present in only 40-70% of cases—its absence does not exclude necrotizing fasciitis 4, 3
• Marked tissue edema occurs in 100% of cases with a characteristic peau d'orange appearance in 90% of pediatric patients 4
• Erythema is present in 90% of cases but is nonspecific 6, 2
• Localized swelling and tenderness are early presenting symptoms 3
• Tachycardia occurs in 70% of cases 4

Distinguishing Features from Simple Cellulitis

• Altered sensorium and systemic toxicity are present in 100% of pediatric cases at presentation—this is a critical distinguishing feature 4
• Wooden-hard feel of subcutaneous tissue extending beyond apparent skin involvement distinguishes fasciitis from cellulitis where tissues remain palpable and yielding 7, 6
• Skin discoloration progressing to bullae formation occurs as the infection advances 2
• Skin necrosis or ecchymoses develop in 70% of cases 7, 6

Critical Pediatric-Specific Pitfall

"Pain out of proportion" is NOT a typical symptom in children, unlike adults—do not rely on this classic adult finding 3. Instead, focus on altered mental status, marked edema with peau d'orange appearance, and systemic toxicity.

Predisposing Factors in Children

Most Important Risk Factors

• Varicella lesions are the most frequent initiating factor, accounting for 25-33% of pediatric cases 2, 4, 5
• Previously healthy children comprise the majority—19 of 20 patients in one large series had no chronic disease or immunosuppression 4
• Other triggers include: intramuscular injections, omphalitis, minor trauma, dental abscess, and topical irritants 2

Comorbidities (Less Common in Children than Adults)

• Malnutrition is present in 36% of pediatric cases 5
• Diabetes mellitus, while the most common comorbidity in adults (70.8%), is far less prevalent in children 8, 9
• Immunosuppression is the main risk factor for mortality when present 5

Diagnostic Approach

Clinical Judgment Remains Paramount

• Only 13-28% of pediatric patients receive the correct diagnosis at admission due to nonspecific early findings 3, 9
• Do not wait for imaging—clinical judgment is the most important diagnostic element, and requesting CT/MRI may delay life-saving intervention 7, 6

Laboratory Findings Have Limited Utility

• Abnormal white blood cell count is present in only 50% of cases 4
• Gram stain is unreliable—negative or shows only one organism in 14 of 19 cases despite polymicrobial infection 4
• Surface cultures are not valuable; only deep tissue specimens obtained during operation provide definitive diagnosis 1, 8

When to Suspect Necrotizing Fasciitis

Systematically assess for these features in any child with soft tissue infection: 6

• Altered mental status with systemic toxicity
• Marked edema with peau d'orange appearance extending beyond erythema
• Wooden-hard subcutaneous tissue on palpation
• Failure to respond to initial antibiotics within hours
• Skin discoloration, bullae, or necrosis

If two or more features are present, proceed immediately to surgical exploration rather than continuing observation—each hour of delay increases mortality 6, 9

Mortality and Prognostic Factors

• Overall mortality ranges from 15-18% in recent pediatric series 3, 5
• Mortality rises to 50-70% when hypotension and organ failure develop 7, 1
• Delay in surgery beyond 24 hours is the single most important modifiable risk factor (relative risk = 9.4) 9
• All survivors in one series underwent aggressive surgical debridement within 3 hours of admission, while all deaths occurred in patients with delayed management 4
• Mean number of operations required is 3.8, with fascial excision of up to 35% of total body surface area sometimes necessary 4