RESUMO
From June 1979 to December 1984 a study was made of the frequency and causes of acute hepatitis, including the fulminant form, in Boca do Acre municipality, in the extreme southwestern corner of the Amazon Basin of Brazil. Serologic studies were done by the radioimmunoassay and enzyme immunoassay techniques. Earlier studies of serologic prevalence had indicated that hepatitis Aand hepatitis B were highly endemic throughout the region and that most people were infected during the first ten years of life. Hepatitis A caused 37 per cent of reported cases; it was the predominant type among children over 5 years of age and produced an epidemic pattern. Hepatitis B accounted for 48 per cent of the cases and was a leading cause of disease in both children and adults. Non-A, non-B hepatitis was encountered chiefly in older adults. The incidence of acute and fulminant hepatitis was 3.33 and 0.365 cases per 1 000 persons/year, respectively. In more than 85 per cent of the cases of fulminant hepatitis there was an active hepatitis B virus infection (HBV) and patient sera tested positive for the hepatitis B surface antigen (HBsAg). The most frequent single cause of fulminant hepatitis was superinfection by delta virus of carriers of HBV. The rates of fulminant acute hepatitis found in Boca do Acre are considerably higher than those reported previously in other parts of Brazil or of the Americas