Diagnosis: Primary Varicella (Chickenpox)
This clinical presentation is classic for primary varicella infection and requires immediate initiation of oral acyclovir 800 mg five times daily for 7–10 days, along with strict isolation until all lesions have crusted. 1
Clinical Diagnosis
The constellation of vesicular lesions beginning on the trunk (abdomen) and spreading to the head, accompanied by fever and nocturnal pruritus, is pathognomonic for primary varicella infection. 1
No laboratory confirmation is needed for this typical presentation. 1 The American Academy of Pediatrics explicitly states that clinical diagnosis alone is sufficient for immunocompetent patients with characteristic varicella findings. 1
Key Diagnostic Features Present:
- Centripetal rash distribution (trunk to head) distinguishes primary varicella from herpes zoster, which follows a dermatomal pattern 1
- Fever of approximately 38.5°C is an expected feature of primary VZV infection 1
- Pruritus is characteristic, as varicella presents as pruritic macules, papules, vesicles, pustules, and crusts 2
- Lesions in varying stages of development (macules → papules → vesicles → pustules → scabs) occur simultaneously 3
- Prodrome of malaise lasting 1–2 days before rash onset is typical 1
Immediate Management
Antiviral Therapy
Start oral acyclovir 800 mg five times daily for 7–10 days immediately. 1 Adults have significantly higher risk of complications than children and benefit substantially from early antiviral therapy when initiated within 24 hours of rash onset. 1
Critical Pitfall to Avoid:
Do not delay treatment waiting for laboratory confirmation in typical cases. 1 Adults experience more severe disease with greater morbidity than children, making prompt antiviral therapy essential. 2, 4
Infection Control Measures
Implement both airborne and contact precautions immediately. 1 Transmission occurs through:
- Direct contact with vesicular fluid
- Aerosolized respiratory droplets
- Respiratory secretions 1
Isolate the patient from all susceptible individuals until all lesions have completely crusted (typically 4–7 days after rash onset). 1 Secondary attack rates reach approximately 90% among susceptible contacts, making varicella extraordinarily contagious. 1
Contact Management:
For exposed household members or close contacts:
- Assess vaccination status immediately 1
- Administer varicella vaccine within 3–5 days for post-exposure prophylaxis 1
- For high-risk susceptible individuals (immunocompromised, pregnant women), give varicella-zoster immune globulin (VZIG) within 96 hours 1
When to Consider Laboratory Testing
Laboratory confirmation is not indicated for this typical presentation. 1 Testing should be reserved only for:
- Atypical presentations
- Immunocompromised patients
- Absence of characteristic features
- Public health surveillance or outbreak investigation 1
If testing were needed, PCR of vesicular fluid provides the highest sensitivity and specificity for VZV detection. 1
Differential Diagnosis to Exclude
Herpes Zoster (Shingles):
- Unilateral dermatomal distribution (not generalized trunk-to-head spread) 1
- Typically occurs in older adults or immunocompromised patients due to VZV reactivation, not primary infection 1
- Painful rather than primarily pruritic 5
Disseminated Herpes Zoster:
- Rare in immunocompetent patients 6
- Would still show initial dermatomal clustering before dissemination 6
Smallpox Vaccination Reactions:
- Eczema vaccinatum presents with vesicular lesions but requires recent vaccination exposure 3
- Not relevant without vaccination history 3
Red Flags Requiring Escalation of Care
Watch for signs requiring IV acyclovir and hospitalization:
- Altered mental status, severe headache, or focal neurologic deficits suggesting VZV encephalitis 7
- Respiratory symptoms suggesting pneumonitis (more common in adults) 2, 6
- Hemorrhagic or bullous lesions indicating severe disease 3
- Immunocompromised state (requires IV acyclovir 10 mg/kg every 8 hours for minimum 21 days) 8