The epidemiology of hepatitis A virus infections in four Pacific Island nations, 1995-2008

Historically, hepatitis A virus (HAV) has been highly prevalent in developing countries, with most infections occurring during childhood, when they are likely to be asymptomatic. Shifts in the acquisition of infection from childhood to adulthood, when clinical hepatitis is more likely, may leave populations vulnerable to large outbreaks. We conducted cross-sectional serosurveys from 1995 to 2008 in four Pacific Island nations to determine the proportion of people previously infected with HAV by measuring antibodies to HAV (anti-HAV). In American Samoa, 0.0% of 4- to 6-year-olds (95% CI 0.0-3.7) were anti-HAV positive. In Chuuk, FSM, 8.6% of 2- to 6-year-olds (95% CI 5.7-11.5) were anti-HAV positive compared with 98.3% of individuals ≥16 years old (95% CI 96.6-100). In Pohnpei, FSM, 0.8% of 2- to 9-year-olds (95% CI 0.0-1.6) were anti-HAV positive compared with 95.1% of ≥16 year-olds (95% CI 92.2-98.0). In RMI, 85.7% (95% CI 81.9-89.5) of 4- to 9-year-olds were anti-HAV positive. In Palau, 0.7% of 7- to 8-year-olds were anti-HAV positive (95% CI 0.0-1.8). The low HAV seroprevalence among children in American Samoa, FSM and Palau may indicate a vulnerability to hepatitis A morbidity among these populations. These data will be useful for evaluating the need for hepatitis A surveillance and vaccination programs.