Do ambient noise exposure levels predict hearing loss in a modern industrial cohort?

BACKGROUND: Much of what is known about the exposure-response relationship between occupational noise exposures and hearing loss comes from cross-sectional studies conducted before the widespread implementation of workplace hearing conservation programmes. Little is known about the current relationship of ambient noise exposure measurements to hearing loss risk. AIM: To examine the relationship between rates of high frequency hearing loss and measured levels of noise exposure in a modern industrial workforce. METHODS: Ten-year hearing loss rates were determined for 6217 employees of an aluminium manufacturing company. Industrial hygiene and human resources records allowed for reconstruction of individual noise exposures. Hearing loss rates were compared to ANSI 3.44 predictions based on age and noise exposure. Associations between hearing loss, noise exposure, and covariate risk factors were assessed using multivariate regression. RESULTS: Workers in higher ambient noise jobs tended to experience less high frequency hearing loss than co-workers exposed at lower noise levels. This trend was also seen in stratified analyses of white males and non-hunters. At higher noise exposure levels, the magnitude of hearing loss was less than predicted by ANSI 3.44 formulae. There was no indication that a healthy worker effect could explain these findings. The majority of 10 dB standard threshold shifts (STS) occurred in workers whose calculated ambient noise exposures were less than or equal to 85 dBA. CONCLUSIONS: In this modern industrial cohort, hearing conservation efforts appear to be reducing hearing loss rates, especially at higher ambient noise levels. This could be related to differential use of hearing protection. The greatest burden of preventable occupational hearing loss was found in workers whose noise exposure averaged 85 dBA or less. To further reduce rates of occupational hearing loss, hearing conservation programmes may require innovative approaches targeting workers with noise exposures close to 85 dBA.