Secular Trends in Hepatitis A Virus Infection among Alaska Natives

To assess the epidemiologic characteristics of the population susceptible to hepatitis A virus (HAV) infection and determine the natural history of infection, a retrospective survey was done using banked serum specimens. A random sample of 4030 Alaska Natives statewide was selected, stratified by year of birth and community of residence. Overall, 1988 serum samples (49.3%) tested positive for antibody to HAV (anti-HAV). Past HAV infection was strongly age-related, increasing from 7% in persons born since 1975 to 85% among persons born before 1945. Prevalence of infection also varied between regions. In small communities, a clear demarcation typically existed between previously infected older persons and younger anti-HAV-negative persons. This indicated that village-wide outbreaks of HAV infection have been the norm and appear to be dependent on the presence of a young susceptible population. Widespread vaccination with hepatitis A vaccine to maintain a high proportion of young anti-HAV-positive persons may be successful in preventing future epidemics. In Alaska the pattern of hepatitis A virus (HAV) infection has typically been one of cyclic recurrences every 10-I 2 years. A statewide epidemic occurred during the mid- 1970s; it peaked in 1976 when > 1000 cases of hepatitis A were reported to the Alaska Division of Public Health. Alaska Natives accounted for >60% of the reported cases, although they constitute only 16% of the state’s population. From that time through the mid- 198Os, the average number of reported cases dropped to 30/year and most cases were associated with occasional common-source outbreaks [ I]. In late 1986, the number of reported cases began to rise. marking the beginning of a new epidemic cycle [2]. In community-wid e outbreaks of hepatitis A, prophylaxis with immune serum globulin generally has not been effective [3] and is costly. Recently, formalin-inactivated whole HAV vaccines have been developed that are immunogenic and efficacious in preventing clinical disease and probably subclinical infection [4]. These vaccines could make the control of widespread epidemics in certain populatio& possible through preexposure vaccination. A retrospective serologic survey was done to assess the epidemiologic characteristics of the natural history of HAV infection among Alaska Natives to determine how immunization against hepatitis A might be used to prevent future epidemics.