Distinguishing Chickenpox from Hand, Foot, and Mouth Disease
Chickenpox and hand, foot, and mouth disease are fundamentally different viral illnesses that can be reliably distinguished by their causative agents, incubation periods, rash distribution patterns, and typical age groups affected.
Causative Agents
- Chickenpox: Caused by varicella-zoster virus (VZV), a herpes virus 1
- HFMD: Caused by enteroviruses, most commonly coxsackievirus A16 and enterovirus 71, though coxsackievirus A6 has emerged as a major pathogen in recent years 2, 3
Incubation Period
- Chickenpox: 14-16 days (range: 10-21 days) 1
- HFMD: 3-7 days (typical for enteroviruses, based on general medical knowledge)
Clinical Presentation & Rash Distribution
Chickenpox 1
- Rash characteristics: Lesions progress through distinct stages (macules → papules → vesicles → pustules → scabs), with all stages present simultaneously ("crops" of lesions)
- Distribution: Concentrated on trunk and head more than extremities (centripetal distribution)
- Number of lesions: 250-500 lesions typically
- Mucosal involvement: Frequently affects mouth, conjunctivae, and other mucosal sites
- Duration: Fever and rash last approximately 5 days
- Contagious period: 1-2 days before rash onset until all lesions are crusted
Hand, Foot, and Mouth Disease 3, 4, 5
- Rash characteristics: Painful papules and vesicles
- Classic distribution: Oral mucosa (enanthem with ulceration), palms, soles, and buttocks
- Atypical presentations (especially with CVA6): Extensive involvement including perioral area, trunk, knees, dorsal hands, and areas of atopic dermatitis ("eczema coxsackium") 3, 6
- Additional features:
- High fever (more prominent with CVA6)
- Onychomadesis (nail shedding) occurring weeks later 4
- Palmoplantar desquamation
- Duration typically 7-10 days
Age Groups Affected
- Chickenpox: Historically affected 5-9 year-olds most commonly, though shifted to 1-4 year-olds in the 1990s; 90% of cases occurred in children <15 years in the prevaccine era 1
- HFMD: Primarily affects children <5 years, with highest attack rates in 1-2 year-olds (33.14%) 6. However, CVA6 increasingly affects adults 3, 5, 7
Complications
Chickenpox 1
- Secondary bacterial infections
- Pneumonia
- Encephalitis
- Reye syndrome (if aspirin used)
- Can reactivate later as herpes zoster (shingles)
HFMD 2, 4
- Severe complications (especially with EV-A71):
- Brainstem encephalitis
- Meningoencephalitis
- Acute flaccid paralysis/myelitis
- Pulmonary edema
- Increased mortality in children <3 years and teenagers with brainstem encephalitis
Management
Chickenpox
- Supportive care for uncomplicated cases
- Antiviral therapy (acyclovir) for high-risk patients, adolescents, adults, or severe disease
- Prevention: Varicella vaccine (Varivax) is highly effective 1
- Isolation until all lesions crusted
HFMD 8, 2
- Supportive care only - no effective antiviral therapies currently available
- Symptomatic treatment for fever and pain
- Prevention: EV-A71 vaccines approved and used in mainland China 2
- Diagnosis confirmed by RT-PCR from vesicle fluid, respiratory samples, or stool 8
Key Diagnostic Pitfalls
Do not confuse atypical HFMD (especially CVA6) with chickenpox - the atypical form can present with widespread vesicular lesions that mimic varicella 3, 9. Critical distinguishing features:
- Chickenpox: Multiple stages of lesions simultaneously, centripetal distribution, longer incubation
- Atypical HFMD: Perioral concentration, palmoplantar involvement, shorter incubation, often occurs in winter (unusual for chickenpox)
When uncertain, viral PCR testing can definitively distinguish between VZV and enterovirus infections 8.