What are the characteristics and management of varicella rash, especially in high-risk populations such as immunocompromised patients, pregnant women, and neonates?

Varicella Rash Characteristics and Management

Rash Distribution and Appearance

Varicella presents with a characteristic centrifugal distribution pattern, beginning on the face and trunk and spreading to the extremities, with lesions appearing simultaneously in different stages of development (macules, papules, vesicles, and crusts) creating a distinctive "starry sky" appearance. 1

Classic Distribution Pattern

• Lesions typically begin on the face and trunk as the initial sites of presentation 1
• Progression is centrifugal: from the center (face/trunk) to the periphery (extremities) 1
• The scalp is frequently involved as part of the facial/cephalic distribution 1
• Unlike smallpox, varicella shows lesions simultaneously in different stages of progression in all affected areas 1

Lesion Evolution

• Lesions appear as erythematous macules that rapidly evolve to papules, then vesicles 1
• The typical rash consists of 250-500 lesions in immunocompetent patients 2
• The disease is usually self-limited, lasting 4-5 days and is characterized by fever, malaise, and the generalized vesicular rash 2

Atypical Presentations

• Varicella may have a modified presentation in areas of skin irritation such as sun exposure, pre-existing inflammation, diaper irritation, operative sites, burns, insect bites, or pre-existing skin disease 3
• In these cases, the rash may be monomorphic and without the typical "starry sky" appearance 3

High-Risk Populations and Complications

Immunocompromised Patients

• Infants, adolescents, adults, and immunocompromised persons are at higher risk for complications 2
• In immunosuppressed hosts, lesions can continue to develop for longer periods (7-14 days or more) 1
• These patients may develop more severe disease with cutaneous dissemination and visceral involvement including viral pneumonia, encephalitis, and hepatitis 4

Pregnant Women and Neonates

• Primary VZV infection in the final 3 weeks of pregnancy may cause transplacental infection and neonatal varicella 5
• Infants are most at risk of severe disease if born from 5 days before to 2 days after onset of the maternal varicella rash 5
• Strict isolation of pregnant women, neonates, and other immunocompromised individuals is mandatory 1

Treatment Approach

Immunocompromised Patients

High-dose intravenous acyclovir is the treatment of choice for VZV infections in immunocompromised hosts. 1, 6

• Dosing for varicella-zoster in immunocompromised patients:
  • Adults and adolescents (≥12 years): 10 mg/kg IV every 8 hours for 7 days 6
  • Pediatrics (<12 years): 20 mg/kg IV every 8 hours for 7 days 6
• Treatment should be continued until clinical response is achieved, then switched to oral acyclovir or valacyclovir to complete 14-21 days of total treatment 1
• Each dose must be infused at a constant rate over 1 hour; rapid or bolus injection must be avoided 6

Neonatal Varicella

• Neonates (birth to 3 months): 10 mg/kg IV every 8 hours for 10 days 6
• Doses of 15-20 mg/kg have been used in neonatal herpes simplex infections, though safety and efficacy for these higher doses are not fully established 6
• Administration of varicella zoster immunoglobulin for post-exposure prophylaxis is advised for neonates at highest risk 5

Immunocompetent Patients

• Severe initial episodes in immunocompetent adults and adolescents: 5 mg/kg IV every 8 hours for 5 days 6
• The vast majority of immunocompetent persons require only symptomatic therapy directed toward reduction of fever and avoiding secondary bacterial skin infection 4

Infection Control

Contagious Period

• The patient remains contagious until all lesions are completely crusted over or no new lesions appear in 24 hours 1
• Peak viral titers occur in the first 24 hours after lesion onset, with progressive decline as lesions convert to crusts 7
• The typical duration of disease is approximately 2 weeks in immunocompetent hosts 1

Prevention

• Postexposure vaccination is effective in preventing illness or modifying varicella severity if used within 3 days, and possibly up to 5 days, of exposure 2
• If exposure does not cause infection, postexposure vaccination should induce protection against subsequent exposure 2

Critical Pitfalls to Avoid

• Do not delay treatment in immunocompromised patients or neonates—initiate IV acyclovir immediately upon clinical suspicion 1
• Do not use rapid or bolus IV injection of acyclovir; this can cause renal toxicity 6
• Do not discontinue isolation precautions until all lesions are fully crusted 1
• Do not miss atypical presentations in areas of pre-existing skin inflammation, which may lack the classic "starry sky" appearance 3
• Adjust acyclovir dosing for renal impairment: patients with creatinine clearance <50 mL/min require dosing interval adjustments 6