Epidemiology of Infectious Diseases: Hepatitis A
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.
- 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.
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).
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.
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.
- Heymann D L, editor, Control of Communicable Disease Manual. 18th ed. American Public Health Association; 2004.
- Department of Health, Health Protection Agency.
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