ANTHOPHYLLITE EXPOSURE AND ENDEMIC PLEURAL PLAQUES IN KUMAMOTO, JAPAN

Objectives This study explored the high prevalence of pleural plaques in the town of Matsubase in Kumamoto, Japan. Methods Small-size chest X-ray film was used for screening, and all persons with pleural plaque s were confirmed by computed tomography (CT). The prevalence rate of p leural plaques in the 4 districts of Matsubase and its surrounding tow ns and cities were also examined. The age-adjusted mortality rate for lung cancer in this town was compared with that of its surrounding tow ns and cities. Results Pleural plaques were found in 1357 persons (724 men and 633 women) among the inhabitants who were more than 20 years of age in Matsubase between 1988 and 1993. CT scans ascertained 938 ca ses with pleural plaques among the 1114 persons who participated. Thus at least 9.5% of the inhabitants over 20 years of age in this town ha d pleural plaques. The neighboring towns had a higher rate than the mo re distant towns. A large-scale opencast asbestos mine and mill had be en in operation in Matsubase between 1883 and 1970. Mineral analysis r evealed anthophyllite fibers. Most of the plaques were found in person s who had never worked in the mine or mill. Conclusions The high preva lence of pleural plaques in Matsubase was due to anthophyllite exposur e, mainly environmental. No mesotheliomas were found, however. These f indings agree with those from an earlier study from Finland.