What are the clinical features of chicken pox?

Clinical Features of Chickenpox

Chickenpox presents as a highly contagious illness with a characteristic pruritic vesicular rash that progresses through distinct stages (macules → papules → vesicles → pustules → crusts), with lesions appearing in successive crops over 4-5 days, resulting in lesions at various stages of development simultaneously—a hallmark feature that distinguishes it from other viral exanthems. 1, 2

Incubation Period and Prodrome

• The incubation period averages 14-16 days (range: 10-21 days) after exposure 1, 3
• A brief prodromal phase may occur with low-grade fever, malaise, and headache, though this is typically shorter and less prominent than in measles 2, 3
• In children, the prodrome is often minimal or absent, with rash appearing as the first noticeable symptom 3

Characteristic Rash Features

Distribution Pattern

• The rash demonstrates centripetal distribution, being most concentrated on the trunk, head, and face rather than the extremities 1, 2
• This trunk-centered pattern is a critical distinguishing feature from smallpox or measles, which show centrifugal distribution (face and extremities predominant) 2
• Lesions frequently develop in the mouth, conjunctivae, and other mucosal sites 1
• Lesions can appear on palms and soles but are less common in these locations 1

Lesion Evolution and Morphology

• Most children develop 250-500 skin lesions in unvaccinated cases 1, 3
• Cutaneous lesions begin as macules and rapidly progress through stages: papules → vesicles → pustules → scabs 1, 2
• The vesicles are described as "dewdrops on a rose petal" appearance—superficial vesicles on an erythematous base 4
• New lesions continue to erupt in successive crops for at least 4-6 days in healthy hosts, resulting in the pathognomonic finding of lesions in various stages of development and resolution simultaneously 2, 3
• This asynchronous development contrasts sharply with smallpox, where all lesions appear at the same time and evolve at the same rate 2

Duration and Resolution

• Fever and rash typically last approximately 5 days 1
• Lesions progress to crusting, with all lesions typically crusted by 4-7 days after rash onset 3
• Bullous or hemorrhagic lesions may occasionally occur 1

Modified Presentation in Vaccinated Individuals (Breakthrough Varicella)

• Fewer than 50 lesions (compared to 250-500 in unvaccinated individuals) 3
• Lesions are more maculopapular than vesicular in nature 3
• Fever is less common and the overall illness is milder 3
• This modified presentation can make clinical diagnosis more challenging 3

Systemic Symptoms

• Pruritus is a prominent and characteristic feature 3, 4
• Low-grade fever is typical 3
• General malaise and discomfort 3
• In immunocompetent children, chickenpox is generally mild with little morbidity 4

Severe Disease in High-Risk Populations

Adults and Adolescents

• More severe disease course with higher rates of complications, particularly pneumonia 3, 5
• Increased morbidity and mortality compared to children 4, 5

Infants

• At higher risk for complications 3
• Infants who acquire chickenpox during the first year of life have an increased risk of developing herpes zoster later 1

Immunocompromised Patients

• Lesions may continue developing over 7-14 days (versus 4-6 days in healthy hosts) 2
• Risk of visceral involvement (lungs, liver, brain) with high morbidity and mortality 4

Pregnant Women

• Can develop severe disease with risk to both mother and fetus 3
• Congenital VZV infection is uncommon but can result in severe congenital malformations 4

Contagiousness

• Highly contagious with secondary attack rates reaching 90% among susceptible contacts 3
• Transmission occurs through direct contact, inhalation of aerosols from vesicular fluid, or infected respiratory tract secretions 3
• Contagious period begins 1-2 days before rash onset and continues until all lesions are crusted 3
• Patients are no longer infectious after all lesions have crusted, typically 4-7 days after rash onset 3

Common Pitfalls in Diagnosis

• Do not confuse with smallpox: Chickenpox has centripetal (trunk-centered) distribution and asynchronous lesion development, while smallpox has centrifugal distribution and synchronous lesion development 2
• Do not confuse with measles: Measles presents with maculopapular (not vesicular) rash, the classic "3 Cs" prodrome (cough, coryza, conjunctivitis), and synchronous lesion development 2
• Breakthrough varicella may be missed: In vaccinated individuals, the atypical presentation with fewer, more maculopapular lesions can lead to misdiagnosis 3
• History of varicella is becoming less reliable: Only 75% of unimmunized children aged 1-4 years who report a positive history of chickenpox are actually seropositive 1