Long-term follow-up study of health status in population living in methylmercury-polluted area.

At present, it is important to follow-up on the health condition of inhabitants living in a methylmercury-polluted area surrounding Minamata City, paying attention to subclinical disorders not only of the central nervous system, which have been concentrically studied for more than 40 years, but also to other health issues as well. We have performed annual follow-up multiple health examinations on about 1,500 persons of ages more than 40 years old in Tsunagi Town near Minamata City each summer from 1984 to 2004. Case-control studies were designed to estimate the role of risk factors for various health issues using geographical differences to compare the verified patients. The results of the study are summarized as follows: (1) There were no significant differences in the prevalence of diseases associated with Minamata disease (MD) (e.g., liver diseases, renal diseases). (2) Subjective complaints, which were related not only to neurological but also to general complaints were consistently much more common in the polluted area than in the control area. (3) Five percent of the inhabitants who were not certified as MD patients had a high predicting index of MD. They could be affected by methylmercury poisoning. It is important to make a differential diagnosis. (4) No significant differences with respect to ADL by residential area were observed. However, MD patients who stayed in their homes showed some impairments of instrumental ADL. (5) It is important to take into consideration mental distress not only from the physical effects but also from the secondary social damage experienced through MD in these area.