title: Radiographic progression of silicosis among Japanese tunnel workers in Kochi.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Environmental Medicine, Kochi Medical School, Kochi University.
authors.forename: Narongpon
authors.initials: N
authors.lastname: Dumavibhat
authors.forename: Tomomi
authors.initials: T
authors.lastname: Matsui
authors.forename: Eri
authors.initials: E
authors.lastname: Hoshino
authors.forename: Sasivimol
authors.initials: S
authors.lastname: Rattanasiri
authors.forename: Dittapol
authors.initials: D
authors.lastname: Muntham
authors.forename: Ryoji
authors.initials: R
authors.lastname: Hirota
authors.forename: Masamitsu
authors.initials: M
authors.lastname: Eitoku
authors.forename: Momo
authors.initials: M
authors.lastname: Imanaka
authors.forename: Basilua Andre
authors.initials: BA
authors.lastname: Muzembo
authors.forename: Nlandu Roger
authors.initials: NR
authors.lastname: Ngatu
authors.forename: Shinichi
authors.initials: S
authors.lastname: Kondo
authors.forename: Norihiko
authors.initials: N
authors.lastname: Hamada
authors.forename: Narufumi
authors.initials: N
authors.lastname: Suganuma
mesh_terms: D000368:Aged; D018450:Disease Progression; D006801:Humans; D007564:Japan / Q000453:epidemiology; D008875:Middle Aged; D013902:Radiography, Thoracic; D012189:Retrospective Studies; D012829:Silicosis / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D001335:Vehicle Emissions / Q000633:toxicity*; D017132:Workplace
chemical_list: D001335:Vehicle Emissions