What are the clinical features of varicella infection?

Clinical Features of Varicella Infection

Classic Presentation in Immunocompetent Patients

Varicella typically presents as a self-limited illness lasting 4-5 days, characterized by fever, malaise, and a generalized pruritic vesicular rash consisting of 250-500 lesions in different stages (crops) of development and crusting. 1

Rash Characteristics

• The rash appears as pruritic macules, papules, vesicles, pustules, and crusts occurring simultaneously in different stages of evolution 2
• Lesions most commonly appear on the back, chest, face, and abdomen, though they can occur on any epithelial surface 2
• The hallmark feature is the presence of lesions in multiple stages of development (polymorphic rash), distinguishing it from smallpox where lesions develop synchronously 1
• Vesicles progress through stages: macule → papule → vesicle → pustule → crust over approximately 4-7 days 1

Systemic Symptoms

• Low-grade fever is typically present, along with malaise 1
• Other systemic symptoms may include headache and general discomfort 1
• The average incubation period is 14-16 days after exposure (range: 10-21 days) 1

Modified Presentation in Vaccinated Individuals (Breakthrough Varicella)

Breakthrough varicella in vaccinated children usually presents with a modified or atypical presentation, with the rash typically being mild and consisting of fewer than 50 lesions that are more likely to be predominantly maculopapular than vesicular. 1

Key Differences from Classic Varicella

• Fewer lesions (typically <50) compared to 250-500 in unvaccinated individuals 1
• Lesions are more maculopapular than vesicular in nature 1
• Fever is less common and when present, is typically lower grade 1
• Shorter duration of illness overall 1
• Despite milder presentation, breakthrough varicella remains infectious, though vaccinated children with <50 lesions are approximately one-third as infectious as unvaccinated children 1

Severe Disease in High-Risk Populations

Immunocompromised Patients

Varicella in immunocompromised patients can present atypically with hemorrhagic, necrotizing, or bullous forms, and may involve internal organs (lungs, liver, brain) resulting in high morbidity and mortality. 3, 2

• Progressive varicella (development of new lesions for >7 days) indicates depressed immune response allowing continued viral replication 4, 5
• Atypical presentations including bullous, hemorrhagic, or necrotizing lesions can complicate diagnosis 3, 6
• Disseminated disease with visceral involvement (pneumonia, hepatitis, encephalitis) is more common 2, 7
• Prolonged viral shedding and slower healing of lesions (7-14 days or longer) 4
• Extended period of contagiousness beyond the typical 4-7 days 4, 5

Adults and Adolescents

• Increased risk for complications compared to children 1
• More severe disease course with higher rates of pneumonia and other complications 6
• Greater likelihood of hospitalization and mortality 1

Other High-Risk Groups

• Infants are at higher risk for complications 1
• Pregnant women can develop severe disease with risk to both mother and fetus 1
• Neonates and premature infants are at increased risk for severe disease 4

Contagiousness and Transmission

• Highly contagious with secondary attack rates reaching 90% among susceptible contacts 1
• Transmission occurs through direct contact, inhalation of aerosols from vesicular fluid, or infected respiratory tract secretions 1
• Contagious period begins 1-2 days before rash onset and continues until all lesions are crusted, typically 4-7 days after rash onset 1, 4
• For non-crusting lesions (macules and papules), contagiousness ends when no new lesions appear within 24 hours 4, 5
• Airborne transmission is possible, particularly documented in healthcare settings 4

Critical Diagnostic Pitfalls to Avoid

• Do not assume mild presentation excludes varicella in vaccinated individuals—breakthrough varicella requires high index of suspicion due to atypical presentation 1
• Do not delay antiviral treatment in immunocompromised patients or those with progressive disease (new lesions >7 days), regardless of timing from initial rash onset 5
• Do not miss atypical presentations in immunocompromised patients, including bullous or hemorrhagic forms that may mimic other conditions like bullous pemphigoid 3
• Do not underestimate contagiousness of breakthrough varicella—even mild cases remain infectious 1