Excess Mortality Resulting From Mixed Exposure To Polychlorinated Biphenyls And Polychlorinated Dibenzofurans From Contaminated Rice Oil: “Yusho”

Introduction: In 1968, rice-oil contaminated with polychlorinated biphenyls and polychlorinated dibenzofurans caused a severe outbreak of food poisoning in Japan, and was termed locally as “Yusho” (oil disease). Epidemiological studies on excess mortality following the outbreak remain limited. In our previous study, we found that area-based standardized mortality ratios (SMRs) of some diseases were elevated shortly after the incident. This previous study, however, was unable to determine whether these elevated SMRs were a result of other area-specific factors. To overcome this limitation, we obtained mortality data from the five years before the incident and conducted an area-based study using vital statistics records dating from 1963 to 2002. Methods: The population of Nagasaki Prefecture was set as the reference population for calculating SMRs. We also included data on cause-specific mortality attributable to cancer and expanded the population to encompass two severely exposed areas where contaminated r...