title: Longitudinal changes in prevalence of respiratory symptoms among Canadian grain elevator workers.
abstract: OBJECTIVE
  To determine longitudinal changes in the prevalence of chronic respiratory symptoms among Canadian grain workers.
  
  
  METHODS
  Data on respiratory symptoms, smoking status, and pulmonary function were obtained approximately every 3 years (termed cycle) over 15 years beginning in 1978 from five regions of Canada.
  
  
  METHODS
  The number of grain workers participating in each cycle were as follows: cycle 1 (n = 5,702); cycle 2 (n = 5,491); cycle 3 (n = 3,713); cycle 4 (n = 2,847); and cycle 5 (n = 3,079).
  
  
  RESULTS
  A procedure based on generalized estimating equations (PROC GENMOD; SAS Institute; Cary, NC) was used to fit marginal models to determine risk factors influencing the prevalence of chronic respiratory symptoms (wheeze, dyspnea, sputum, and cough). The prevalence (predicted probability based on the final model) of chronic respiratory symptoms had an increasing trend with increasing number of years in the grain industry from cycle 1 to cycle 3 (before dust control) for all three smoking categories (current smokers, ex-smokers, and nonsmokers). For cycle 4 and cycle 5 (after dust control), there was a reduction in the prevalence of these respiratory symptoms. For example, in cycle 1, the prevalence of chronic wheeze among current smoking grain workers increased from 12% (for those in the industry for < 5 years) to 44% (for those in the industry for > 35 years); in cycle 5, the prevalence of chronic wheeze among current smoking grain workers increased from 9% (for those in the industry for < 5 years) to 28% (for those in the industry for > 35 years). Similar trends were observed for ex-smokers and nonsmokers and for other chronic respiratory symptoms.
  
  
  CONCLUSIONS
  Our results indicate that grain dust control was effective in reducing the prevalence of chronic respiratory symptoms among grain workers in all smoking and exposure categories.
authors.affiliation: Institute of Agricultural Rural and Environmental Health, University of Saskatchewan, Royal University Hospital, 103 Hospital Dr, Saskatoon, SK, S7N OW8, Canada.
authors.forename: Punam
authors.initials: P
authors.lastname: Pahwa
authors.forename: Helen H
authors.initials: HH
authors.lastname: McDuffie
authors.forename: James A
authors.initials: JA
authors.lastname: Dosman
mesh_terms: D000328:Adult; D002170:Canada / Q000453:epidemiology; D002523:Edible Grain / Q000009:adverse effects*; D004607:Elevators and Escalators; D006801:Humans; D019570:Inhalation Exposure / Q000009:adverse effects*; D008137:Longitudinal Studies; D008875:Middle Aged; D009784:Occupational Diseases / Q000453:epidemiology* / Q000517:prevention & control; D016273:Occupational Exposure / Q000009:adverse effects*; D016272:Occupational Health; D011314:Preventive Health Services; D012120:Respiration Disorders / Q000453:epidemiology* / Q000517:prevention & control; D012129:Respiratory Function Tests