Mortality and Survival for Minamata Disease

Abstract

Analysis of mortality of 439 deaths that occurred among 1483 patients with Minamata disease (MD) in Kumamoto Prefecture, Japan was performed from the end of 1981. Causes of death and survival rates were studied by means of the standardized mortality ratio (SMR) and life-table technique. Of the 439 deaths (29.6%) in MD cases, the first death occurred in 1954. There was a first peak incidence in 1956 when MD was initially reported, however, the majority of deaths occurred after 1972 when a second and much larger peak was evident. In 1970 an important milestone occurred when the Public Nuisance Relief Law (an anti-pollution law) was enacted. Among its provisions, this law required and enabled verification of MD among people suspected of having been exposed. In contrast to the early cases, later cases of MD were older and their mean age-at-death was not different from that of the general population. The mortality rate for all causes of death was significantly higher in both sexes compared to the general population. Significantly lower survival rates were noted for older patients. The cause specific mortality rates also showed significantly increased SMRs for liver diseases and nephritis-nephrotic syndrome in male patients, and for nephritis-nephrosis-nephrotic syndrome and other diseases in females. On the other hand, the SMR for senility without mention of psychosis was significantly lower than expected in both sexes.