Two years' follow-up investigation of a hepatitis E virus (HEV) outbreak in West Kalimantan, Indonesia in 1991 was carried out to investigate the epidemiology of epidemic HEV transmission and the persistence of the immunoglobulin G (IgG) antibody response. Sixty cases identified as anti-HEV IgG positive during the outbreak in 1991 were matched with 67 controls and examined, together with 318 members of their families. Overall, the prevalence of anti-HEV IgG among the 445 subjects (representing 127 households) was 59%. There was no significant difference in anti-HEV prevalence between cases (72%) and controls (61%). Loss of detectable anti-HEV IgG after 2 years was demonstrated in 17 of 60 subjects (28%) who were originally positive for anti-HEV in 1991. The mean number of anti-HEV positive subjects per household was 2.04. Cross-sectional prevalence of anti-HEV IgG increased significantly with age (P = 0.01). When communities were grouped into areas of low (< 40%), medium (40-59%) and high (> or = 60%) anti-HEV prevalence, use of river water for drinking and cooking (P < 0.001), personal washing (P < 0.0001), and human excreta disposal (P < 0.001) were associated with high prevalence communities. Conversely, boiling drinking water was negatively associated with increased prevalence (P = 0.02). Subnormal rainfall during the month (August) leading up to the 1991 outbreak (19 cm compared to the monthly mean of 209 cm in 1985-1993) may have contributed to favourable epidemic conditions.