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 > or = 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 prevalence 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 > or = 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.(ABSTRACT TRUNCATED AT 250 WORDS)