Risk factors for human alveolar echinococcosis: a case-control study in Hokkaido, Japan

A case-control study to determine the risk factors for human alveolar echin ococcosis (AE) was conducted in Hokkaido, Japan. The 134 cases were either patients clinically diagnosed as having AE (N=61) or other individuals foun d to be seropositive for Echinococcus multilocularis although showing no ab normalities in ultrasound scans (N=73). Two groups of case-matched controls were employed: one of 670 individuals selected from a list of residents of Hokkaido (group A) and the other of 650 subjects selected from a list of i ndividuals who had been found seronegative in earlier investigations (group B). Because of the long latency of AE, potential risk factors were studied over two different periods: for the 0-10 and 11-20 years before the year o f diagnosis/recorded seropositivity. The results of multivariate analyses, in which the cases were compared with each control group, indicated that th e rearing of cattle and pigs and the use of well water were significant ris k factors and that the use of tap water significantly decreased the risk of an individual having AE. Extension of the piped water supply and health ed ucation on improving the disposal of household rubbish (to keep foxes away from houses) should help reduce the risk of AE infection in the study area.