Small epidemic of hepatitis E in the fall 2009 in Sapporo, Hokkaido

Abstract

In Sapporo and its surrounding areas, we encountered 11 successive cases of acute sporadic hepatitis E between late September and late October in 2009. Surprisingly, the HEV strains, obtained from the patients, segregated to a compact cluster in genotype 4, suggesting that the epidemic was caused by the propagation of single source strain. In addition, these HEV strains were closely related not only to "Sapporo strain" previously reported, but also to "Kitami/Abashiri strain", which caused acute hepatitis several years ago in Kitami and Abashiri regions, located far away from Sapporo. Despite intensive surveillance by the Hokkaido Study Group for Hepatitis E, neither a common infection source nor precipitating event for epidemic could be identified. The advanced system for food distribution may have spread the HEV strains, thereby complicating identification of the source of HEV infection. "New Sapporo strains" should be carefully monitored in the future.