What age groups are commonly affected by hand‑foot‑and‑mouth disease, and can an individual experience multiple episodes due to different viral strains?

Hand-Foot-and-Mouth Disease: Age Distribution and Reinfection Risk

Hand-foot-and-mouth disease primarily affects children under 5 years of age, with the highest incidence in those aged 1-3 years, and yes, individuals can absolutely experience multiple episodes because different enterovirus serotypes do not provide cross-protection against each other 1, 2, 3.

Age Groups Most Commonly Affected

The disease shows a clear age predilection:

• Children under 5 years account for the vast majority of cases, with approximately 88% of hospitalized patients being under 4 years old 4
• The 1-3 year age group represents the largest proportion at 62.76% of cases 4
• Infants between 1 month and 1 year also represent a significant vulnerable population 4
• While traditionally considered a childhood illness, adults are increasingly recognized as susceptible, particularly with atypical and sometimes more severe presentations 5, 6

Age-Specific Clinical Patterns

The clinical presentation varies significantly by age:

• Neonates (≤1 month) present with lower rates of typical rash and herpangina but have significantly higher cerebrospinal fluid protein levels and higher rates of aseptic meningitis (73.33%) 4
• Children aged 1-3 years have the highest rate of convulsions (21.48%) 4
• Children over 3 years show higher rates of intracranial hypertension (24%) 4

Multiple Infections Are Common

Yes, individuals can and do experience HFMD multiple times due to the lack of cross-protection between different enterovirus serotypes:

Reinfection Epidemiology

• The reinfection rate is approximately 2.60% among documented cases 7
• The median time interval between primary and secondary infection is 12.75 months 7
• Reinfection peaks seasonally from June to August 7

Risk Factors for Reinfection

Boys aged 5 years and below are at highest risk for reinfection, particularly those with these characteristics 7:

• Male gender (independent risk factor)
• Younger age (under 5 years)
• Severe cases during primary infection
• Primary infection with EV-A71 (OR=1.83,95% CI=1.29-2.60) - these patients are nearly twice as likely to experience reinfection 7
• Hospitalization during first episode

Why Multiple Infections Occur

The causative agents include multiple enterovirus serotypes:

• Enterovirus A71 (EV-A71) and Coxsackievirus A16 are the traditional main culprits 1, 8, 2
• Coxsackievirus A6 and A10 are causing increasing numbers of infections in recent years 8
• Other Coxsackievirus B strains (B1-B6) can also cause disease 5

Because immunity is serotype-specific and does not cross-protect against other enterovirus strains, a child who recovers from infection with one serotype remains susceptible to all other circulating serotypes 1, 7. This explains why reinfection is not only possible but relatively common in endemic areas.

Important Clinical Caveats

• The current EV-A71 vaccine approved in China only protects against EV-A71-related HFMD, not against other causative enteroviruses, which limits its overall protective effect given the circulation of multiple pathogens 1, 2
• Extensive recombination events among enterovirus strains contribute to faster evolution and extinction of dominant serotypes, making the epidemiological landscape constantly shifting 8
• Severe complications including brain stem encephalitis occur more frequently in children under 3 years and can be fatal 8