A 6-year-old child presents with fever, malaise, and a diffuse maculopapular rash that progresses to vesicles in crops over 3 days. The rash is most concentrated on the trunk and face. Which is the most common complication of varicella-zoster virus (VZV) infection in immunocompetent children?

Explanation

## VZV Complications in Immunocompetent Children **Key Point:** Bacterial superinfection of varicella lesions is the most common complication in immunocompetent children, occurring in 2–10% of cases. *Staphylococcus aureus* and *Streptococcus pyogenes* are the usual pathogens. **High-Yield:** VZV complications vary by immune status: | Complication | Incidence in Immunocompetent | Incidence in Immunocompromised | Pathophysiology | |--------------|------------------------------|--------------------------------|------------------| | Bacterial superinfection | 2–10% (most common) | Higher | Direct invasion of open lesions | | Encephalitis | 0.1–0.2% | 10–20% | Direct CNS invasion | | Pneumonitis | 0.4–0.5% (rare) | 15–30% | Viral dissemination to lungs | | Post-herpetic neuralgia | Common in elderly | Variable | Nerve damage; rare in children | | DIC | < 0.01% (very rare) | Possible | Severe disseminated disease | **Clinical Pearl:** Bacterial superinfection typically occurs 3–7 days after the appearance of vesicles, when lesions rupture and become colonized. Impetigo-like lesions with purulent drainage are hallmark signs. Prevention includes nail trimming and avoiding scratching. **Mnemonic:** **SEPIA** — Superinfection, Encephalitis, Pneumonitis, Immunocompromise, Age (elderly at risk for PHN). ## Why Bacterial Superinfection Is Most Common 1. **High frequency:** Occurs in 2–10% of immunocompetent children—far more common than encephalitis (0.1–0.2%) or pneumonitis (0.4–0.5%). 2. **Mechanism:** Varicella lesions are open wounds; scratching introduces skin flora (*S. aureus*, *S. pyogenes*) into the dermis. 3. **Clinical significance:** Can lead to cellulitis, abscess formation, or rarely, invasive disease (toxic shock syndrome). ## Why Other Options Are Less Common - **Encephalitis:** Occurs in only 0.1–0.2% of immunocompetent children; much more common in immunocompromised hosts. - **Pneumonitis:** Rare (0.4–0.5%) in children; more common in adults and immunocompromised patients. - **DIC:** Extremely rare (< 0.01%) in immunocompetent children; seen only in severe disseminated disease.