What is the workup and treatment for a patient with suspected varicella-zoster virus (VZV) infection?

Workup and Treatment for Varicella-Zoster Virus (VZV) Infection

For patients with suspected varicella-zoster virus infection, diagnosis should be made through direct testing of vesicular fluid using PCR or direct fluorescent antibody assay, followed by prompt antiviral therapy with acyclovir, valacyclovir, or famciclovir, with treatment regimens based on clinical presentation and immune status.

Diagnostic Approach

Clinical Presentation

• Primary varicella (chickenpox):

  • Generalized, pruritic, vesicular rash (250-500 lesions)
  • Lesions in different stages of development and crusting
  • Low-grade fever and systemic symptoms
  • In vaccinated individuals: milder, atypical presentation

• Herpes zoster (shingles):

  • Unilateral, vesicular eruption with dermatomal distribution
  • Prodromal pain 24-72 hours before rash appearance
  • Evolution from erythematous macules to papules to vesicles
  • Lesions coalesce, form bullae, and scab before healing

Laboratory Diagnosis

• Recommended tests 1:

  • PCR of vesicular fluid (highest sensitivity and specificity, approaching 100%)
  • Direct fluorescent antibody assay of lesion material
  • Viral culture (less sensitive than PCR)

• Not recommended for acute diagnosis:

  • Serology (not useful for diagnosing active chickenpox or shingles)
  • Tzanck smear (cannot differentiate between VZV and HSV)

• Timing of specimen collection:

  • Collect vesicular fluid from unruptured vesicles when possible
  • PCR can detect VZV DNA even in crusted lesions 1

Treatment Algorithm

1. Uncomplicated Herpes Zoster in Immunocompetent Adults

• Recommended therapy 1, 2, 3:
  • Oral acyclovir: 800 mg 5 times daily for 7-10 days, OR
  • Oral valacyclovir: 1 gram 3 times daily for 7 days (preferred due to better bioavailability)
  • Famciclovir is also an acceptable alternative
  • Continue treatment until all lesions have scabbed 1

2. Primary Varicella (Chickenpox)

• Immunocompetent children 2:

  • Children (2 years and older): Acyclovir 20 mg/kg (maximum 800 mg) 4 times daily for 5 days
  • Adults and children >40 kg: Acyclovir 800 mg 4 times daily for 5 days
  • Initiate therapy at earliest sign of infection (within 24 hours of rash onset)

• Immunocompromised patients 1, 4:

  • Intravenous acyclovir: 10 mg/kg (or 500 mg/m²) every 8 hours
  • Continue until all lesions have scabbed

3. Complicated or Disseminated VZV Infection

• Disseminated zoster or severe infection 1, 4:

  • Intravenous acyclovir: 10 mg/kg every 8 hours
  • Temporary reduction in immunosuppressive medications if applicable
  • Consider transition to oral therapy after clinical improvement
  • Continue until all lesions have scabbed

• VZV with CNS involvement 5:

  • Intravenous acyclovir: 10 mg/kg every 8 hours for adults (500 mg/m² for children)
  • Minimum 7 days of treatment
  • Consider steroid therapy (prednisone 60-80 mg/day for 3-5 days) for VZV vasculopathy

4. Dose Adjustments for Renal Impairment

• Acyclovir dose modification 2:
  • CrCl >25 mL/min: No adjustment
  • CrCl 10-25 mL/min: 800 mg every 8 hours
  • CrCl <10 mL/min: 800 mg every 12 hours
  • Hemodialysis: Additional dose after each dialysis session

Post-Exposure Prophylaxis

For Susceptible High-Risk Individuals

• Recommended approach 1:
  • Administer varicella zoster immune globulin (VZIG) within 96 hours of exposure
  • Target populations: immunocompromised patients, pregnant women, neonates
  • If VZIG unavailable or >96 hours have passed: oral acyclovir for 7 days, started 7-10 days after exposure

For Healthcare Settings

• Infection control measures 6:
  • Implement airborne and contact precautions until all lesions are dry and crusted
  • Only healthcare personnel with evidence of immunity should care for patients with VZV
  • Exposed susceptible healthcare workers should be excluded from duty from day 8 after first exposure through day 21 after last exposure

Special Considerations

Immunocompromised Patients

• Treatment modifications 1:
  • Higher doses and longer duration of antiviral therapy may be required
  • Consider IV therapy even for localized disease
  • Monitor for potential antiviral resistance in patients on prophylactic antivirals
  • Reduce immunosuppressive medications temporarily if possible

Prevention Strategies

• For high-risk patients 1:
  • Screen for VZV IgG in patients with uncertain history or who grew up in tropical/subtropical climates
  • Vaccinate seronegative patients before initiating immunosuppressive therapy
  • Complete vaccination at least 3 weeks before starting immunosuppressants

Common Pitfalls to Avoid

1. Delayed treatment: Initiate antiviral therapy immediately upon clinical suspicion, don't wait for test results 1
2. Inadequate dosing: VZV requires higher antiviral doses than HSV infections 1
3. Inappropriate diagnostic testing: Don't rely on serology for acute diagnosis 1
4. Overlooking complications: Monitor for secondary bacterial infections, particularly in immunocompromised patients 1
5. Insufficient isolation: Maintain appropriate isolation precautions until all lesions are crusted 6