Iranian Journal of

Background and Objectives: Noise-induced hearing loss is a prevalent work-related morbidity in the country. We determined the strength of association between hearing loss and occupational noise exposure as the first step in prevention programs.
Material and Methods: A historical cohort study involving 100 exposed and 31 non-exposed subjects was conducted. Noise exposure was estimated using sound level meter BSEN 60651, Type 2. Past noise exposure was estimated using the existing data on the place and type of work. Audiometry was used to assess hearing loss in each subject in 3- year intervals on an occupational cohort from 1993-2004.

Results: Noise-induced hearing loss was found in 49% (49 subjects) of the exposed group and 9.7 %( 3 subjects) of non-exposed group (p<.0001). Nobody used any form of hearing protection routinely in either group. Relative risk for noise-induced hearing loss was 5.1(CI95%: 1.7- 15.1).Time at risk was estimated 24.9 years (22.7-27.1) in exposed and 22.2 years (20.7-23.7) in unexposed group by survival analysis.
Conclusion: More legislation, hearing conservation programs, and surveillance and biological monitoring of work sites and workers are required to prevent occupational hearing loss. Planning strategies for noise assessment and control can help improve the work environment. Gross occupational exposure to noise has been demonstrated to cause hearing loss and the authors believe that occupational hearing loss in the country is a widespread problem.