Clinical Overview

Varicella (chickenpox) is a common, highly contagious viral infection caused by varicella-zoster virus (VZV), affecting approximately 90% of unvaccinated children. The disease is characterized by a distinctive centripetal vesicular rash preceded by prodromal symptoms. While generally self-limited in immunocompetent children, varicella carries significant complications including secondary bacterial skin infections (5-10%), pneumonia (0.1-2%), and encephalitis (0.1%). Varicella vaccine (VAR) has reduced incidence by >90% in vaccinated populations. Early antiviral therapy with acyclovir can reduce disease duration and severity if started within 24 hours of rash onset.

Epidemiology

Varicella affects 90% of unvaccinated populations, with peak incidence between ages 3-10 years before vaccine introduction. With routine VAR vaccination, incidence has declined >90% in vaccinated populations. Secondary attack rate in unvaccinated household contacts exceeds 90%. Varicella shows marked seasonality with peak incidence in late winter/early spring in temperate climates. The disease can affect any age, though severity increases significantly in adolescents and adults. Immunocompromised children and pregnant women have much higher complication rates.

Pathophysiology

VZV, a human herpesvirus, enters via respiratory epithelium and replicates in regional lymph nodes. Initial viremia at 4-6 days post-exposure disseminates virus to skin and mucous membranes. Secondary viremia (10-14 days) causes the characteristic rash as immune response controls viral replication. Lesions begin in the dermis and epidermis, progressing from erythematous macules to vesicles to pustules to crusts over 3-5 days. The centripetal distribution (more on trunk and face than extremities) is characteristic. Virus remains latent in sensory nerve ganglia lifelong, capable of reactivation as herpes zoster.

Clinical Presentation

Varicella presents with 1-2 days of prodromal symptoms: fever (often 38-39°C), malaise, headache, and anorexia. Rash appears first on face and trunk, then spreads to extremities. Individual lesions begin as erythematous macules (within hours becoming tiny papules), progress to clear vesicles on red bases ("dewdrop on rose petal"), then become pustular, and finally crust over within 3-5 days. Pruritus is intense, often leading to complications from scratching. Oral lesions (enanthem) may be present on palate, typically less numerous than skin lesions. Fever typically resolves as rash peaks (around day 3-4), then gradually improves. Most children are completely well by day 7-10.

Diagnosis

Clinical diagnosis is reliable based on characteristic centripetal vesicular rash in stages of development. Tzanck smear (multinucleated giant cells) may support diagnosis but is not specific. PCR from vesicular fluid provides definitive diagnosis. Viral culture from vesicular fluid is less sensitive but confirms diagnosis. IgM serology or IgG-ELISA confirms infection if diagnosis is clinically uncertain. Electron microscopy showing herpesvirus particles supports diagnosis.

Treatment (Age-Specific)

Infants (6-12 months): Supportive care is mainstay. Acetaminophen 15 mg/kg/dose every 4-6 hours for fever (maximum 5 doses/24 hours). AVOID IBUPROFEN (associated with invasive Group A Streptococcus). Maintain hydration with breast milk, formula, or oral rehydration solution. Keep skin clean with frequent baths to prevent secondary bacterial infection. Oatmeal baths may soothe pruritus. Trim fingernails short to prevent scratching damage.

Antiviral therapy (if started <24 hours after rash onset): Acyclovir 10-20 mg/kg/dose intravenously every 8 hours for 7-10 days for hospitalized patients. Oral acyclovir is less effective in infants due to absorption variability.

Children 1-12 years: Supportive care with acetaminophen 15 mg/kg/dose every 4-6 hours (maximum 40 mg/kg/day). Antiviral therapy recommended for children >12 months if started within 24 hours: acyclovir 20 mg/kg/dose orally four times daily for 5 days (maximum 800 mg/dose). Valacyclovir 20 mg/kg/dose orally three times daily for 5 days (maximum 1000 mg/dose) is alternative with better bioavailability. Famciclovir 250-500 mg three times daily for children >12 years.

Secondary bacterial infection: Amoxicillin-clavulanate 45 mg/kg/day (amoxicillin component) divided twice daily for 10 days. For penicillin allergy: cephalexin 25-50 mg/kg/day divided four times daily, or azithromycin 10 mg/kg/day once daily for 5 days.

Adolescents (12+ years): Varicella is more severe in this age group. Antiviral therapy is strongly recommended: acyclovir 800 mg orally five times daily for 5-7 days, or valacyclovir 1000 mg three times daily for 5 days, or famciclovir 500 mg three times daily for 5-7 days. Acetaminophen 325-650 mg every 4-6 hours for fever.

Prognosis

Most immunocompetent children recover completely within 7-10 days without sequelae. Complications occur in 1-2% of otherwise healthy children but increase significantly in immunocompromised patients. Secondary bacterial infections (impetigo, cellulitis) occur in 5-10% and are most common complication. Pneumonia (0.1-2%), encephalitis (0.1%), and toxic shock syndrome are serious but rare. Post-herpetic neuralgia is rare in children but increases significantly with age. Varicella vaccination significantly reduces disease incidence and severity.

When to See a Pediatric Dermatologist

Dermatologic evaluation confirms diagnosis if uncertain. Specialist assessment is needed for extensive secondary bacterial infection, unusual presentations, or complications. Immunocompromised children require close monitoring and specialist involvement.

FAQ

Q: Should I give my child ibuprofen for chickenpox fever?
A: No, AVOID ibuprofen in chickenpox as it's associated with invasive Group A Streptococcus infections and severe complications. Use acetaminophen (15 mg/kg/dose) for fever management instead. This is an important safety concern specific to chickenpox.

Q: When can my child return to school or daycare?
A: Children should remain home until all lesions are crusted over (typically 5-7 days after rash onset). Most schools require documentation that all lesions are crusted. Once crusted, the infection is no longer contagious through respiratory secretions.

Q: Should I treat chickenpox with antiviral medication?
A: Antiviral therapy (acyclovir, valacyclovir, or famciclovir) can reduce disease duration by 1-2 days if started within 24 hours of rash onset. For most healthy children, this modest benefit doesn't require treatment. However, it's recommended for adolescents (who have more severe disease) and should be considered for any child at higher risk for complications.

Q: How do I prevent my child from scratching and getting infected lesions?
A: Keep fingernails short and clean. Use mittens or soft cotton gloves if necessary. Oatmeal baths can help soothe itching. Keep the skin clean with frequent gentle washing. Applying calamine lotion (non-drying formulations) may help. If secondary infection develops, seek prompt medical evaluation.

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