A cohort study on mortality of "yusho" patients: a preliminary report.

In 1968, a mass food poisoning (yusho) occurred in western Japan involving more than 1,850 people, the majority of whom were residents of Fukuoka and Nagasaki prefectures. The poisoning is now understood to have been caused by ingestion of a commercial brand of rice oil contaminated with polychlorinated derivatives of biphenyls, dibenzofurans, quaterphenyls, and some other related compounds. The number of deaths seen among 1,761 victims (887 males and 874 females) from the date of official registration as yusho up to the end of 1983 was compared with the expected number of deaths which was calculated on the basis of the national age, sex, and cause-specific death rates. Neither significantly increased nor significantly decreased mortality was seen among overall causes of death in males and females. A significant excess mortality was seen for malignant neoplasms at all sites in males but not in females. Neither significantly increased nor decreased mortality was seen for cancer of the esophagus, stomach, rectum and colon, pancreas, breast, and uterus. For cancer of the liver, however, a considerably increased mortality was seen in both males and females but the excess was statistically significant only in males. It was also notable that such increased mortality due to liver cancer was seen mainly among the patients living in Fukuoka prefecture but not at all among those in Nagasaki prefecture which approximate the yusho patients in Fukuoka prefecture in number. Deaths from chronic liver diseases and liver cirrhosis were also found to be increased in both sexes but the increase was not statistically significant.