The impact of hearing conservation programs on incidence of noise-induced hearing loss in Canadian workers.

BACKGROUND: Noise exposure remains one of the most ubiquitous of occupational hazards. Hearing conservation program legislation and the programs themselves were designed to lower risk of resulting occupational noise-induced hearing loss, but there has been no broad-based effort to assess the effectiveness of this policy. METHODS: The incidence of a 10-dB standard threshold shift was examined in a group of Canadian lumber mill workers, using annual audiogram series obtained from the Workers' Compensation Board of British Columbia for the period 1979-1996 and using Cox proportional hazard models. RESULTS: Mean cumulative noise exposure was 98.1 dB-years. The audiograms from 22,376 individuals, among whom there were 2,839 threshold shifts of 10 dB or greater (i.e., a "standard threshold shift"), were retained in multivariable analyses. After adjusting for potential confounders, continuous use of hearing protection, and initial hearing tests later in the study period, the risk for standard threshold shift was reduced by 30%. Risk increased sixfold, however, in those with the highest noise exposure. CONCLUSIONS: Hearing conservation programs may be effective in reducing overall incidence of hearing loss. In the absence of noise control at source, however, highly exposed workers remain at unnecessary risk.

Diffuse lamellar keratitis complicating laser in situ keratomileusis: post-marketing surveillance of an emerging disease in British Columbia, Canada, 2000-2002.

PURPOSE: To describe a surveillance system and summarize data between January 2000 and December 2002 regarding diffuse lamellar keratitis (DLK), a complication of laser in situ keratomileusis (LASIK) surgery. SETTING: Community-based clinics in British Columbia, Canada, in which LASIK surgery is performed. METHODS: Monthly, all clinics in which LASIK is performed reported the number of LASIK procedures and nonnominal cases of DLK (by grade and onset date) to the British Columbia Centre for Disease Control. Diffuse lamellar keratitis outbreaks were investigated, and prevention and control measures were recommended. RESULTS: From 2000 to 2002, approximately 72,000 LASIK procedures were performed, with a mean DLK incidence rate of 0.67% (95% confidence interval, 0.61-0.73). The overall proportion of DLK cases attributed to outbreaks was 64%, decreasing from 72% in 2000 to 40% in 2003. CONCLUSIONS: An effective DLK surveillance program was implemented at all laser refractive clinics in British Columbia. Reported DLK incidence was 0.67 cases per 100 procedures, with 64% occurring in outbreaks.

Exposure levels and determinants of softwood dust exposures in BC lumber mills, 1981-1997.

Measurements of personal exposure to wood dust (n = 1237) collected by the Workers' Compensation Board of British Columbia, Canada, over the period 1981-1997 were used to construct an empirical model to identify broad determinants of softwood dust exposure. Potential determinants of exposure examined included species of tree processed; company; geographic location of lumber mill; department; job title; calendar year; and production factors such as board feet of lumber produced per year. A determinants of exposure model was built using multiple linear regression. Nested within this compliance database was a subset of samples collected for a research study. These enabled the authors to explore whether differences in exposure measurements can in part be explained by sampling strategy (research versus compliance). Potential differences were examined by examining differences in means for each job title, stratified by sampling strategy; and by offering "sampling strategy" as a categorical predictor variable to the empirical model. Multiple linear regressions revealed the most important determinants of increased wood dust exposure to be mill location away from the coast, earlier calendar year, and indoor jobs. The empirical model had an R2 of 0.39 and a predictive range from 0.02 to 25.45 mg/m3. Research and compliance sampling strategies showed no difference in mean exposure and distribution in the empirical model (p < 0.05), suggesting that regulatory exposure databases may be of utility for exposure assessment in epidemiology. This research indicates that compliance-sampling strategies do not result in an overestimation of mean exposure levels within jobs, but they do focus on a biased sample of jobs-those most highly exposed.