Progression of pneumoconiosis in coal miners after cessation of dust exposure: a longitudinal study based on periodic chest X-ray examinations in Hokkaido, Japan.

Background The progression rate of pneumoconiosis in retired coal miners over ten years has not been studied in Japan. Methods A retrospective longitudinal study was undertaken using chest X-rays of 1091 pneumoconiosis subjects in Hokkaido, Japan between 1985 and 2005. Results The final numbers of subjects were 207 (19% of the entry) after 1 decade and 85 (8%) after 2 decades. Sixty-two percent of 207 subjects after 1 decade and 29% of 85 showed progression in 2 decades. Thirty-one percent of ILO category 1 and 55% of category 2 subjects showed progression to complicated pneumoconiosis after 1 decade, and 6% (4 of 64) of category 1 and 6% (5 of 77) of category 2 subjects progressed to complicated pneumoconiosis during 2 decades. Conclusion The progression of pneumoconiosis was observed after the cessation of dust exposure, especially during the first 10 years.