Objectives Occupational noise-induced hearing loss (NIHL) is prevalent, yet evidence on the effectiveness of preventive interventions is lacking. The effectiveness of a new technology allowing workers to monitor daily at-ear noise exposure was analysed.
Methods Workers in the hearing conservation program of an aluminium smelter were recruited because of accelerated rates of hearing loss. The intervention consisted of daily monitoring of at-ear noise exposure and regular feedback on exposures from supervisors. The annual rate of change in high frequency hearing average at 2, 3 and 4 KHz before intervention (2000–2004) and 4 years after intervention (2006–2009) was determined. Annual rates of loss were compared between 78 intervention subjects and 234 controls in other company smelters matched for age, gender and high frequency hearing threshold level in 2005.
Results Individuals monitoring daily noise exposure experienced on average no further worsening of high frequency hearing (average rate of hearing change at 2, 3 and 4 KHz=–0.5 dB/year). Matched controls also showed decelerating hearing loss, the difference in rates between the two groups being significant (p<0.0001). Analysis of a subset of intervention subjects matched to controls for initial rate of hearing loss showed a similar trend but the difference was not statistically significant (p=0.06).
Conclusion Monitoring daily occupational noise exposure inside hearing protection with ongoing administrative feedback apparently reduces the risk of occupational NIHL in industrial workers. Longer follow-up of these workers will help determine the significance of the intervention effect. Intervention studies for the prevention of NIHL need to include appropriate control groups.
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Funding This work was supported by the National Institute for Occupational Safety and Health, grant no. 1 R01 OH008641-01A2.
Competing interests Several of the authors (PMR, DG, SRK, MDS, MRC) provide consultant services to Alcoa Inc. One author (CDE) serves as the corporate audiologist for Alcoa Inc.
Ethics approval This study was conducted with the approval of the Yale Human Investigation Committee (HIC), Yale University School of Medicine, and the Institutional Review Board of Stanford University.
Provenance and peer review Not commissioned; externally peer reviewed.
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