EPIDEMIOLOGY OF HEPATITIS-B INFECTION IN NORTH-AMERICA

Although the USA is considered an area of 'low' endemicity for hepatitis B infection, the incidence of new cases, the prevalence of carriers, and the burden of acute anti chronic disease place hepatitis B among the most important communicable diseases. It is estimated that 300 000 new cases of hepatitis B infection occur each year. These acute infections lead to 350-450 fulminant deaths, 27 000-42 000 chronic carriers and ultimately 4000-5500 deaths per year from cirrhosis and primary liver cancer, Most reported cases occur among young adults, many of whom belong to 'high risk' groups defined by lifestyle ol occupation. In 1991, sexual transmission was the predominant mode of transmission (41% of cases by heterosexual activity; 14% by homosexual activity); percutaneous drug use was also important (12% of cases). Infection in healthcare workers represented only 2% of reported cases, and is the only group where falling incidence is due to vaccine use. However 26% of cases occur in people who deny belonging to any 'high risk group.' Public health officials ill the USA concluded that the 'high risk group' immunization strategy would riot lead to the control ol of hepatitis B infection on a population basis. In 1992, it was recommended that all newborns in the USA receive hepatitis B vaccine as part of their routine immunization schedule. The incidence of hepatitis B in Canada has doubled since 1980 according to official reports, falling off from a peak in the late 1980s to 9.9 pet 100 000 population in 1991. The incidence of hepatitis B is highest in the years of most sexual activity, from the age of 15 through the 30s. Universal vaccination of 11-year-olds was implemented in 1992 to curb the spread of hepatitis B.