Outbreak of hepatitis B virus in recent arrivals to the Brazilian Amazon.

An outbreak of acute hepatitis cases in a small community took place 6 months after the community's arrival to the Brazilian Amazon. An epidemiological investigation was performed and included residents aged more than two years. Study subjects were interviewed and bled to test for hepatitis markers by enzyme immunoassays. Around 80% of the village population was surveyed. The overall prevalence of hepatitis B virus (HBV) markers was 75.1% (281/374). The surface antigen of HBV (HBsAg) and the IgM class antibody against hepatitis B core antigen (IgM anti-HBc) were present in 10.4% and 9.6%, respectively. Evidence of HBV-HDV (Delta virus) coinfection or hepatitis C infection was not found. IgM class antibody against hepatitis A virus was uncommon (3.7%). Follow-up evaluation 6 and 12 months later were carried out to identify new HBV infections. An incidence rate of 7.2 new infections per 100 exposed subjects per month was found. Average individual risk for HBV infection among susceptible inhabitants of the village between June 1995 and June 1996 can be estimated at 57.6%. The predominant HB-sAg subtype found (ayw3) suggests that immigrants may have carried HBV from the original area. Time living in the study region was significantly associated with HBV markers in analysis for linear trend and logistic regression analysis. Environmentally related factors may have facilitated HBV transmission.