EPIDEMIOLOGY OF HEPATITIS-A - SEROEPIDEMIOLOGY AND RISK GROUPS IN THE USA

Surveillance and seroepidemiological data are important in determining optimal hepatitis A vaccine strategies. In the USA, after a decade of declining rates, reported hepatitis A rates gradually increased from 9.2 cases per 100 000 population in 1983 to a peak of 14.4 per 100 000 in 1989. In 1991, 23 144 cases were reported, for a rate of 9.1 per 100 000. Since 1983, rates in males have been consistently 20% higher than in females. Rates in children, adolescents and adults up to 39 years old have been roughly equivalent and approximately threefold higher than for persons greater-than-or-equal-to 40 years old. Among reported cases in 1989, the most commonly reported risk factor was personal contact with a hepatitis A case (26%), followed by employment or attendance at a day-care centre (14%), a history of injecting drug use (11%), a history of recent international travel (4%), and association with a suspected food or waterborne outbreak (3%). Of cases, 42% had no known risk factor for infection. The prevalance of antibody to hepatitis A virus in the general US population was 38.2%, based upon testing of 9516 participants.from the second National Health and Nutrition Examination Survey conducted.from 1976 to 1980. Prevalence increased steadily with age, ranging from 11% in persons < 5 years of age to 74% in persons greater-than-or-equal-to 50 years old. Because some groups may be difficult to vaccinate prior to disease exposure (contacts of cases) or are difficult to reach (drug users or persons with unidentified risk), a selected risk group vaccination strategy may not be successful in reducing the disease burden in the USA. High seropositivity in older age groups indicates that prevaccination screening for susceptibility might be considered.