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Canada Communicable Disease Report

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Volume: 27S3 • September 2001

Viral Hepatitis and Emerging Bloodborne Pathogens in Canada

Hepatitis A and Its Control

Jun Wu, Shimian Zou and Antonio Giulivi


Introduction

Infection with the hepatitis A virus (HAV) results in inflammation of the liver and is an important cause of acute jaundice in some age groups. HAV is one of the main causes of hepatitis in humans, accounting for 20%-40% of acute hepatitis in adults. Presentation of hepatitis A infection typically includes flu-like symptoms, which cannot be distinguished from other types of acute hepatitis. The distribution of hepatitis A is geographically related to socioeconomic conditions. Increasing number of studies from around the world suggest that the epidemiologic pattern of hepatitis A is changing where hygienic and socioeconomic conditions are improving. Different countries are responding to these changes by adopting different immunization strategies against HAV. Thus, vaccination programs may be targeted at specific high-risk groups or the entire population. This article reviews recent information on hepatitis A in Canada and in other countries.

Transmission routes

The most common mode of transmission of hepatitis A is via the fecal-oral route, either directly through interpersonal contact or indirectly through ingestion of contaminated food or water. The latter is more common when an outbreak occurs. Risk factors for hepatitis A transmission vary in importance around the world. In developing countries, food-borne or water-borne infections are common, whereas in North America the most commonly identified risk factor is household or sexual exposure to a recent case(1-3). Overall, individuals at increased risk include residents of communities with high rates of infection, children and staff of day-care centres, staff and residents of long-term care facilities, injection drug users, gay men, and international travellers.

Incidence and prevalence

Hepatitis A may occur either in epidemics or as sporadic cases. In developing countries, the incidence of hepatitis A in adults is relatively low because of exposure to HAV in childhood. In areas of low endemicity, the incidence of HAV infection among young children is low, and the proportion of susceptible individuals, especially young adults, is high. Hepatitis A is the seventh most commonly reported infectious disease in the United States and accounts for as many as 65% of all viral hepatitis cases identified each year. It has been estimated that approximately 150,000 people become infected with HAV and more than 28,000 hepatitis A cases are reported each year in the United States. Data collected over several decades show that hepatitis A incidence peaks cyclically about every 10 years(2). The highest incidence of hepatitis A is in children: nearly 30% of reported cases occur in children younger than 15 years of age. The risk for susceptible travellers to developing countries has been estimated at 3-5 per 1,000 per month, higher in those who eat or drink in places with poor hygienic conditions.

Hepatitis A is reportable in Canada. Like most industrialized countries, Canada has a relatively low incidence of hepatitis A: each year 1,000-3,000 cases are reported. It is generally accepted that the true incidence of HAV infection is considerably underestimated as a result of under-reporting of clinical illness and the occurrence of subclinical infections in children(3). The reported hepatitis A rates vary with age group and sex, rates among males being higher than among females. Since there is no evidence indicating that males are more susceptible to hepatitis A than females(4), differences in exposure factors could be responsible for these higher rates. The rates of reported hepatitis A infection in Canada vary significantly among provinces and territories, the highest rates being observed in British Columbia. Geographic and sex differences suggest the need to determine related risk factors and population subgroups with higher risk of hepatitis A, and to develop vaccination options for particularly "at-risk" groups.

As already indicated, HAV infection is closely associated with socioeconomic and hygienic conditions. As living standards improve, the incidence and prevalence of hepatitis A decline, but at the same time the average age of exposure and subsequent infection increases. These changes in epidemiologic pattern have been taking place around the world in recent decades(5,6) and are important, because clinical severity is directly related to the age of infection. Older age groups experience more severe and prolonged clinical illness. On the other hand, natural immunity in the population as a whole decreases, particularly in children, adolescents, and young adults. As a result, the overall number of susceptible individuals in the population increases, creating the potential for hepatitis A outbreaks to occur.

Studies indicate that immunity to HAV infection occurs in about 3% of Canadian-born pre-adolescents but increases with age, and is over 60% for those 60 years of age and older. The most dramatic increase in the rate of HAV seropositivity has been noted between the 20-29 and 30-39 year age groups, increasing from 25% to 46%(7).

Prevention

Intervention measures include early detection of infected individuals, interruption of transmission, and protection of the susceptible population. The most important prevention measure is interrupting HAV fecal-oral transmission by promoting good personal hygiene, proper food handling practices, and provision of clean drinking water and effective sanitary facilities. Other prevention measures include active immunization with hepatitis A vaccines and passive immunization with immune globulin.

Hepatitis A vaccines contain a killed or inactivated virus. The immunologic response takes about 4 weeks to become established, and antibodies persist for at least 1 year after the first dose. Booster doses, given at 6 months or later, confer long-term immunity(8). Studies to date indicate that antibodies are sustained for at least 3 years after vaccination(9). Patients with suppressed immune systems may require more doses of the vaccine than a person with a healthy immune system in order to develop an immunological response.

In Canada, hepatitis A vaccine is currently recommended by the National Advisory Committee for Immunization (NACI) for individuals at increased risk(1). These include travellers to countries where hepatitis A is endemic; residents of communities with high endemic rates or recurrent outbreaks of HAV; members of the armed forces; emergency relief workers and others likely to be posted abroad at short notice to areas with high rates of HAV infection; residents and staff of institutions for the developmentally challenged, where there is an ongoing problem with HAV transmission; inmates of correctional facilities, in which there is an ongoing problem with HAV infection; people with lifestyle-determined risks of infection, such as intravenous drug use, and men who have sex with men; people with chronic liver disease who may not be at increased risk of infection but are at increased risk of fulminant hepatitis A; and others, such as patients with hemophilia A or B receiving plasma-derived replacement clotting factors, zoo-keepers, veterinarians, certain researchers who handle non-human primates, and certain workers involved in research on hepatitis A virus or production of hepatitis A vaccine.

According to the supplementary statement on hepatitis A vaccine by NACI, in 2000(10), HAV vaccine without immune globulin is the preferred method of post-exposure immuno-prophylaxis against this disease, because immune globulin is unlikely to be more effective than HAV vaccine, and is sometimes difficult to obtain. For example, when an outbreak of hepatitis A occurs, an epidemiologic investigation may be initiated to define the scope and cause of the outbreak, and immunization is administered to close contacts of cases as soon as possible to prevent the further spread of infection.

If rapid protection is needed, or active immunization is not suitable or available, human immune globulin is recommended. The efficacy of immune globulin has been shown to be up to 80% to 90% when the product was administered within 2 weeks of exposure(11). Immune globulin is still the recommended immunoprophylaxis for infants and those who may not respond fully to the vaccine, e.g. immunocompromised patients.

Future challenges

With the changing epidemiologic pattern of hepatitis A, it is not certain whether vaccination of higher risk groups alone will be sufficient to prevent the transmission of HAV in the general population. The changing dynamics of HAV infection in different populations indicate that continuous study and surveillance are needed to provide evidence for further decision making.

Universal childhood vaccination is not currently recommended in Canada. Before a recommendation for universal vaccination is made, it will be necessary to determine the cost-effectiveness of such a program. This should take into account the effectiveness of the implementation of universal hepatitis B vaccination in all provinces and territories and the availability of combined hepatitis A and hepatitis B vaccines in Canada. A project, initiated and funded by Health Canada, is currently being carried out by an expert working group. The results from this study will contribute to the assessment of whether universal immunization against hepatitis A would provide a cost-effective strategy for preventing infection in Canada.

References

  1. Canadian immunization guide, 5th edition. Ottawa: Health Canada, 1998 (Minister of Public Works and Government Services Canada, Cat. No. H49-8/1998E).

  2. Shapiro CN, Coleman PJ, McQuillan GM et al. Epidemiology of hepatitis A: seroepidemiology and risk groups in the USA. Vaccine 1992;10(suppl 1):S59-62.

  3. Gust ID. Epidemiological patterns of hepatitis A in different parts of the world. Vaccine 1992;10(suppl 1):S56-58.

  4. Barros H, Oliveiri F, Miranda H. A survey on hepatitis A in Portuguese children and adolescents. J Viral Hepat 1999;6(3):249-53.

  5. Sawayama Y, Hayashi J, Ariyama I et al. A ten year serological survey of hepatitis A, B and C viruses infections in Nepal. J Epidemiol 1999;9(5):350-54.

  6. Beran J, Douda P, Rychly R. Seroprevalence of viral hepatitis A in the Czech Republic. Eur J Epidemiol 1999;15(9):805-8.

  7. LCDC. Seroprevalence of hepatitis A antibodies in travellers at the Edmonton travellers' health clinic - Alberta. CCDR 1995;21(8):65-76.

  8. Furesz J, Scheifele DW, Palkonyay L et al. Safety and effectiveness of the new inactivated hepatitis A virus vaccine. Can Med Assoc J 1995;152(3):343-8.

  9. Berger R, Just M. Vaccination against hepatitis A: control 3 years after the first vaccination. Vaccine 1992;10(suppl 1):S295-99.

  10. National Advisory Committee of Immunization. Supplementary statement on hepatitis A vaccine. CCDR 2000;26(ACS-4):12-18.

  11. Mosley JW, Reisler DM, Brachott D et al. Comparison of two lots of immune serum globulin for prophylaxis of infectious hepatitis. Am J Epidemiol 1968;87:539-550.

We would like to acknowledge Dr. Paul Sockett, Chief of the Enteric, Foodborne/Waterborne Division, Bureau of Infectious Diseases, Health Canada, for his review of this paper.

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