Vaccine-Preventable Diseases

Hepatitis A

Hepatitis A virus (HAV) is an RNA virus of a single serotype. Infection usually causes clinical hepatitis in adults and school-aged children but is often asymptomatic in younger children. Jaundice develops in < 10% of children 6 years and under. Typical symptoms of illness include anorexia, nausea, fatigue, fever and jaundice. The severity of the illness increases with age. Recovery often takes 4 to 6 weeks but may take months. Recurrent hepatitis for up to a year occurs in about 15% of cases, but longer chronic infection is not known to occur. About 25% of reported adult cases require hospitalization. Fulminant disease with liver necrosis is rare but can be fatal. Individuals with pre-existing chronic liver disease are at increased risk of serious complications from HAV infection. The overall estimated case fatality rate associated with hepatitis A is 0.1% to 0.3%, but this rises to 1.8% in persons over the age of 50. It reaches 12.5% in patients over the age of 60 who are hospitalized because of the disease.

Epidemiology

HAV is most frequently transmitted by the fecal-oral route, through direct contact with infected people or indirectly through ingestion of contaminated water or foods. On rare occasions, transmission has been reported after exposure to HAV-contaminated blood or blood products. It also occurs through sexual activities that include direct or indirect oro-anal contact but not through exposure to saliva, semen or urine. The virus may persist for days or weeks in the environment. Shedding of the virus in feces and thus maximum infectiousness occurs during the latter part of the incubation period with peak levels in the 2 weeks before clinical illness. Infectiousness diminishes rapidly thereafter and ends shortly after the onset of jaundice. Humans are the principal reservoir for HAV. Persistent infection does not occur. The incubation period ranges from 15 to 50 days with an average of 20 to 30 days. Lifelong immunity usually follows infection.

In Canada, between 1990 and 2004 the number of cases of HAV infection reported annually varied from 3,562 (1991) to 396 (2003), representing rates of 10.8 and 1.2 per 100,000 population respectively. During this period, there have been outbreaks involving men who have sex with men (MSM) in major Canadian cities. Since the introduction of the vaccine in 1996, no new major outbreak has occurred, and the incidence rate has slowly decreased. It is not known whether this is due to the impact of the targeted immunization programs. There is no information on the proportion of targeted groups being immunized, but it is likely low. The estimated coverage in MSM at the end of the massive immunization campaign during the Montreal outbreak was only 35%. Within Canada, there have been considerable geographic variations in the reported incidence, and this is observed even during periods of decline nationally. In the 5 year period of 1999 to 2004, no substantial sex difference in reported rates was observed. In 2004, the reported rate was 1.4 among females and 1.6 among males per 100,000 population. Age-specific incidence was highest among those 15-24 years old with a rate of 2.3 per 100,000 population, followed closely by those aged 5-14 (2.2 per 100,000 population).

Given asymptomatic infection, underdiagnosis and underreporting, the actual number of cases has been estimated to be 10 times higher than the number of notifications. A nationwide Canadian seroprevalence study has shown a seroprevalence of 2.0% in unvaccinated 8- to 13-year-olds. In this same study, HAV antibody prevalence was 1.1% in non-vaccinated, non-Aboriginal children born in Canada who did not travel to endemic countries. There are no other nationwide seroprevalence data. A systematic review of all seroprevalence studies conducted in Canada has been published recently and demonstrates an increase with age, which is probably due both to the cumulative incidence with increasing age and a cohort effect attributable to higher incidence rates in the past.

Risk factors for HAV infection in Canada include the following:

• Sexual behaviours involving anal contact, particularly between men (MSM). This resulted in the major outbreaks of the 90s.
• Travel to or residence in countries with endemic hepatitis A. In recent years 40% of all notified hepatitis A cases have been in travelers. Among those, 40% are taking low-risk trips (staying for short periods of time in luxury hotels where meals are provided). More than 5 million Canadians go to an HAV-endemic country in a year. Over 5 years, 30% of Canadians will travel to an endemic country, yet less than 15% of these travelers go to a travel clinic and receive hepatitis A vaccine.
• Immigrants or children of new Canadians who return to their country of origin to visit friends and relatives.
• Household contacts of an acute case.
• Residence in certain communities in rural or remote areas lacking adequate sanitation or a secure supply of potable water.
• Residence in certain institutions, such as correctional facilities and those for developmentally challenged individuals.
• Illicit drug use. In this group, transmission is seldom related to contaminated injection material. It is rather associated with a number of risk factors: low hygiene standards, contaminated drugs, and sharing of materials for oral or nasal use of drugs.

More than 25% of cases have no identifiable risk factor. Food handlers are not at higher risk of hepatitis A because of their occupation. However, food handlers may belong to a demographic group with a higher incidence of hepatitis A and thus cause major outbreaks. They may also trigger very extensive public health interventions that become necessary when a food handler is found to be contagious, even if the number of secondary cases is ultimately small.

Source: Canadian Immunization Guide, 7^th edition, 2006

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Links to more information

Guidelines and Recommendations

• For information about Hepatitis A Vaccine, see the Canadian Immunization Guide, 7^th edition 2006

Information Sheets

• Hepatitis A Fact Sheet

Travel Medicine Program

• Hepatitis A

Additional Resources

• Viral Hepatitis and Emerging Bloodborne Pathogens in Canada