Radiographic Progression of Silicosis among Japanese Tunnel Workers in Kochi

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  • Dumavibhat Narongpon
    Department of Environmental Medicine, Kochi Medical School, Kochi University Department of Preventive and Social Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University
  • Matsui Tomomi
    Department of Environmental Medicine, Kochi Medical School, Kochi University
  • Hoshino Eri
    Clinical Trial Center, Kochi Medical School, Kochi University
  • Rattanasiri Sasivimol
    Section for Clinical Epidemiology and Biostatistics, Faculty of Medicine Ramathibodi Hospital, Mahidol University
  • Muntham Dittapol
    Section for Clinical Epidemiology and Biostatistics, Faculty of Medicine Ramathibodi Hospital, Mahidol University
  • Hirota Ryoji
    Department of Environmental Medicine, Kochi Medical School, Kochi University
  • Eitoku Masamitsu
    Department of Environmental Medicine, Kochi Medical School, Kochi University
  • Imanaka Momo
    Department of Environmental Medicine, Kochi Medical School, Kochi University
  • Muzembo Basilua Andre
    Department of Environmental Medicine, Kochi Medical School, Kochi University
  • Ngatu Nlandu Roger
    Department of Environmental Medicine, Kochi Medical School, Kochi University
  • Kondo Shinichi
    Department of Occupational Medicine, Kinro Clinic
  • Hamada Norihiko
    Department of Radiology, Kochi Medical School, Kochi University
  • Suganuma Narufumi
    Department of Environmental Medicine, Kochi Medical School, Kochi University

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Objective: The aim of our study was to investigate the natural course of silicosis in terms of radiographic progression among Japanese tunnel workers. Methods: Tunnel workers with silicosis were included in our study between January 2008 and June 2011. We retrospectively assessed workers' radiographs from their first through last visits to see whether there was progression. All films were interpreted by two physicians, who had been specially trained in using the ILO (2000) International Classification of Radiographs of Pneumoconioses (ILO/ICRP). We classified the radiographic findings according to the ILO/ICRP. Survival analysis was performed and then presented as time to progression. Subgroup analysis among the progressed group was performed to demonstrate duration of progression. Results: A total of 65 patients, who were no longer exposed to silica for the duration of the study, were included. The mean age at the first visit was 58.60 ± 7.10 years. The incidence rate of progression was 42 per 1,000 person-years with a median time to progression of 17 years. Progression was demonstrated among 33 cases (51%). The mean durations of progression from category 1 to category 4 and category 2 to category 4 were 14.55 and 10.65 years, respectively. Most patients (86%) had radiographic change from category 1 or 2 directly to category 4. Conclusion: Silicosis progressed at a relatively high rate among tunnel workers without further silica exposure. The high probability of progression directly from category 1 to category 4 may lead to further investigation for the improvement of disease prevention.(J Occup Health 2013; 55: 142–148)

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