What are the diagnostic criteria and management options for varicella?

Varicella Diagnosis

Varicella is diagnosed clinically by the presence of acute onset diffuse papulovesicular rash without other apparent cause, and laboratory confirmation is only required when the clinical presentation is atypical or for public health surveillance purposes. 1

Clinical Diagnostic Criteria

The CDC defines a clinical case of varicella as: 1

• Acute onset of illness
• Diffuse (generalized) papulovesicular rash
• No other apparent cause for the rash

Key Clinical Features to Identify

The characteristic presentation includes: 1

• Crops of lesions in different stages of development (papules, vesicles, crusts appearing simultaneously)
• 250-500 lesions in unvaccinated persons 1
• Pruritic vesicular rash with lesions progressing from macules to papules to vesicles 1
• Low-grade fever and systemic symptoms typically present 1
• Lesions continue erupting for 4-6 days in immunocompetent hosts 2

Important caveat: In vaccinated children, the presentation is often modified and atypical with fewer lesions (often <50), predominantly maculopapular rather than vesicular, and milder systemic symptoms. 1, 3 This requires a high index of suspicion. 1

Laboratory Confirmation

Laboratory testing is indicated when: 1

• Clinical presentation is atypical
• Patient is immunocompromised
• Confirmation needed for public health purposes
• Outbreak investigation required

Diagnostic Testing Options

Preferred methods (in order of sensitivity/specificity): 1

1. PCR (nucleic acid amplification) - Most sensitive and specific (approaching 100% for both), can detect VZV DNA even in crusted lesions 1

   • Sample: Vesicular fluid or scab scraping from disrupted lesion 1

2. Direct fluorescent antibody (DFA) assay - Rapid detection of viral antigens 1

   • Sample: Vesicular fluid or lesion scraping

3. Viral culture - VZV-specific culture from vesicular fluid 1

   • Less sensitive than PCR, requires viable virus

4. Serology - Significant rise in varicella IgG antibody between acute and convalescent sera 1

   • Not useful for acute diagnosis of active infection 1
   • Useful for determining immunity status before exposure

Common pitfall: Serology is not helpful for diagnosing acute chickenpox or shingles. 1 Use direct viral detection methods instead.

Case Classification

According to CDC surveillance definitions: 1

• Probable case: Meets clinical definition, not laboratory confirmed, and not epidemiologically linked to another case
• Confirmed case: Either laboratory confirmed OR meets clinical definition AND epidemiologically linked to a confirmed/probable case

Key point: Two probable cases that are epidemiologically linked are considered confirmed even without laboratory testing. 1

Management Considerations After Diagnosis

Isolation Requirements

• Isolate immediately upon diagnosis 4
• Patient is infectious from 2 days before rash onset until all lesions are crusted 1
• Requires well-ventilated room with infection control precautions 4

Antiviral Treatment Indications

Acyclovir or valacyclovir should be started promptly (within 72 hours of rash onset) for: 1, 5, 4

• Adults
• Immunocompromised patients (use IV acyclovir 5-10 mg/kg every 8 hours) 2, 5
• Severe disease or complications
• Pregnant women
• Neonates

Immunosuppressive therapy should be discontinued in severe cases during active infection. 1, 5

High-Risk Complications to Monitor

Be vigilant for: 1, 4, 6

• Bacterial superinfection (especially invasive group A streptococcal infections) - increasing in frequency 6
• Pneumonia - more common in adults 1, 4
• Encephalitis 1
• Hepatitis 4
• Visceral dissemination in immunocompromised patients 2, 4

Critical warning: Adults have a 13 times higher hospitalization rate and 25 times higher mortality rate compared to children aged 5-9 years. 1 Infants <1 year have 6 times higher hospitalization rates. 1