[Exposure to high level of noise and hearing loss; a cohort study]

ABSTRACT

Regarding the high prevalence of hearing loss among workers with long-term exposure to high level of noise, the importance of recognizing hearing loss etiology and assessing the effect of occupational health efforts to reduce the effect of noise pollution on hearing of workers, the present study is designed in the two groups of workplaces with and without high levels of noise in Rafsanjan [2006]. In this historical cohort study, 120 workers were randomly selected in two groups; 1- sixty workers who had exposure to high level of noise [mean level of noise > 85 dB] and 2- sixty workers who did not have this exposure. Age, gender, experience and the daily working time among workers in the two groups were similar. Pure Tone Audiometry method was used for measuring hearing situation and the threshold considered for hearing loss was 20 dB. The proportions of workers with hearing loss in the two groups were compared using Chi-Square test, relative risk [RR] was calculated and 95% confidence interval for the target population was estimated. Mean level of noise in the workplaces with and without high level of noise were 108.3 +/- 6.0 and 68 +/- 4.0 dB, respectively [P<0.0001]. There were 12% and 73% [P<0.0005] of respondents in exposed and none exposed groups who were suffering from hearing loss in their right ear giving a relative risk of 4. These proportions for hearing loss in left ear were 15% and 60% [p<0.0001], respectively, giving a relative risk of 6.3. Workplaces with high level of noise which may cause hearing loss for workers still exist in the area of the study. More investigations are needed to explore the barriers and more occupational health efforts must be made to reduce the negative consequences