Hepatitis A

Epidemiology of Infectious Diseases: Hepatitis A

Causal Agent
Hepatitis A is caused by infection with the hepatitis A virus (HAV), a positive stranded RNA virus, first identified in 1973.

Common clinical features

  • Infection with HAV may range from asymptomatic to symptoms of fever, malaise, abdominal pain, loss of appetite, nausea, vomiting and diarrhoea followed by dark urine and jaundice.
  • In young children infection with HAV is usually asymptomatic whereas symptomatic disease occurs more commonly among adults.
  • Approximately 15% of infected individuals will have prolonged illness or relapsing symptoms over 6-9 months.
  • Case fatality is low, around 0.6% increasing with age to 1.8% in adults over 50 and 10% in adults aged over 701.
  • Protective antibodies develop in response to infection and confer lifelong immunity.
  • No chronic infection is known to occur.

Geographical distribution

  • Endemic worldwide, prevalence is higher in countries with poor sanitation and hygiene.
  • In developing countries with high endemicity the peak age of infection occurs largely in early childhood, among whom HAV infection is mostly asymptomatic.
  • In countries where Hepatitis A is highly endemic, exposure to HAV is almost universal before the age of 10 years.
  • In countries with low endemicity the peak age of infection occurs mainly among adults.
  • The incidence of HAV has been decreasing in developed countries over the last 50 years.
  • Notifications of HAV in England and Wales declined from 7,316 in 1992 to 784 in 20042.

Reservoir
Humans

Mode of transmission

  • Person to person, primarily through the faecal-oral route.
  • Contaminated food and water.
  • Contaminated raw shellfish harvested from sewage contaminated water.
  • Blood exposure (rare).

Incubation period
15-50 days, average 28-30 days.

Period of Communicability
From 2 weeks before the onset of symptoms until 1 week after. Maximum infectivity occurs during latter half of the incubation period and for a few days after onset of jaundice.

Diagnosis
Demonstration of IgM antibodies to HAV (IgM anti HAV) in serum.

Prevention and control

  • Personal hygiene, especially among children in child day care and in schools.
  • Vaccination advised for travellers (aged 5 and above) to countries outside Western Europe, North America and Australasia.

References

  1. Heymann D L, editor, Control of Communicable Disease Manual. 18th ed. American Public Health Association; 2004.
     
  2. Department of Health, Health Protection Agency.  

Further resources:

Crowcroft, NS, Walsh B, et al: Guidelines for the control of hepatitis A virus infection, Communicable Disease And Public Health 2001; 4: 213-27. Available at http://www.hpa.org.uk/cdph/issues/CDPHvol4/No3/HepAguidelines0901.pdf

© CM Kirwan 2006