ready present (Tong et al., 1995). This condition resolves with prednisone treatment (Tong et al., 1995). Very rarely fulminant hepatitis associated with coma and occasionally death may occur (Wasley et al., 2010). In most cases of hepatitis A infection, all symptoms and the infection resolve completely (Gordon et al., 1984; Tong et al., 1995).

The fecal-oral route is the most common mode of transmission for hepatitis A. An individual with HAV is most infectious, with highest stool HAV concentrations, during the 2 weeks prior to appearance of jaundice (Fiore et al., 2008). Transmission from a person with active infection may occur through food preparation, household contact, and sexual contact (Fiore et al., 2008). Because children with HAV are frequently asymptomatic, they may serve as reservoirs of disease in households and close-contact environments such as day care (Smith et al., 1997; Staes et al., 2000). HAV has been transmitted through blood transfusion; however, screening has greatly reduced this risk (Soucie et al., 1998). Finally, HAV is resistant to most organic solvents, detergents, and heat, and can survive in the environment (Fiore et al., 2008; Murphy et al., 1993; Peterson et al., 1983). As a result, HAV can be transmitted by food and water contamination, as well as through contact with infected soil and marine sediment (Fiore et al., 2008). Food and waterborne hepatitis is generally associated with contamination by HAV-infected workers, sewage contamination, and inadequate water treatment (Bergeisen et al., 1985; Bloch et al., 1990; Dalton et al., 1996; De Serres et al., 1999; Fiore, 2004).

From 1980 through 1995, reports of hepatitis A to the Centers for Disease Control and Prevention (CDC) numbered between 22 and 36 thousand cases per year (CDC, 2006). Approximately 33 percent of reported cases were in children less than 15 years old (CDC, 2008), and outbreaks of hepatitis A were reported among injection and noninjection drug users and men who have sex with men (Cotter et al., 2003; Harkess et al., 1989; Hutin et al., 1999; Schade and Komorwska, 1988).

Prior to the development and licensure of a vaccine, immune globulin, a sterile solution of antibodies collected and purified from a large group of donors, was used to prevent hepatitis A in those likely to be exposed or recently exposed to the virus (Fiore et al., 2008). In 1995–1996, inactivated vaccines for hepatitis A became available, and since 1999 the CDC has reported a significant decrease in HAV infection in the United States—markedly a 76 percent decrease in 2003 when compared to 1990– 1997 (Wasley et al., 2005). Currently, three inactivated vaccines—Havrix (GlaxoSmithKline Biologicals), VAQTA (Merck & Co., Inc.), and Twinrix (GlaxoSmithKline)—are available in the United States. In these vaccines, the virus is grown in MRC-5 cell cultures and harvested by cell lysis (Fiore et al., 2008). From there, the virus is inactivated and purified through various methods before being packaged with (Havrix and Twinrix) or without (VAQTA) a preservative (Fiore et al., 2008).

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