FRI Briefings Hepatitis

We know how the hepatitis A virus (HAV) is spread, but foodborne enteric viruses remain a difficult problem to control. An outbreak affecting 153 schoolchildren and staff in Michigan this spring emphasizes the need for continued vigilance. The frozen strawberries implicated in this outbreak were grown in Mexico and then packaged in a California plant before being distributed to schools (1). The origin of HAV in this outbreak has not been established. Viral contamination may have occurred during picking in the strawberry fields of Mexico and/or during processing in the California plant. Although HAV is spread most commonly by direct person-to-person contact, there are many documented outbreaks of hepatitis A in the USA and other industrialized countries which have been traced to an infected food handler or some local source of contamination. Postings to the FSNet listserve (2) and Promed's web site on monitoring infectious diseases (3) since the beginning of the year include descriptions of food-and waterborne hepatitis A outbreaks in Los Angeles, Pennsylvania, Iowa and nearby midwestern states, Sweden, Australia, Russia, and Mexico, in addition to the outbreak in Michigan. These are, undoubtedly, only a fraction of the cases which actually occurred. It has been estimated that about one-third of the U.S. population has been exposed to HAV (4). According to the Centers for Disease Control and Prevention (CDC), 31,582 cases of hepatitis A were reported in the USA in 1995 but the real incidence of this disease is estimated to be 138,000 cases/year (5). Not all of these were food-or waterborne. In fact, the majority of hepatitis A cases probably result from fecal–oral transfer during close contact with an infected person. Nevertheless, in its report on cases of foodborne disease outbreaks in the USA during 1988–1992, the CDC lists HAV as the fourth leading cause of foodborne disease (6). Numbers of hepatitis A cases in the USA wax and wane in approximately 10-year cycles. The last peak was in 1989, with 35,821 cases reported (7). Outbreaks are most often associated with consumption of salads, fresh fruits or vegetables, or shellfish, such as oysters. Multiple types of hepatitis viruses are known to exist but only HAV is commonly associated with foodborne illness. Hepatitis E virus has been associated with waterborne illness whereas hepatitis B, C, and D are spread only through body fluids. HAV is an RNA virus which is quite resistant to drying and is more heat …