Purpose: Longitudinal analysis of audiometric data of a large population of noise-exposed workers provides insight into the development of noise-induced hearing loss (NIHL) as a function of noise exposure and age, particularly during the first decade of noise exposure.
Methods: Data of pure-tone audiometry of 17,930 construction workers who underwent periodic occupational hearing screening at least twice during a 4-year period were available for analysis. These concerned all follow-up measurements of the baseline cohort described by Leensen et al. (Int Arch Occup Environ Health 84:577-590, 2011). Linear mixed models explored the relationship between the annual rate of change in hearing and noise exposure level, exposure duration, and age. Data of 3,111 workers who were tested on three occasions were used to investigate the pattern of hearing loss development.
Results: The mean annual deterioration in hearing in this study population was 0.54 dB/yr, and this became larger with increasing noise exposure level and increasing age. Remarkably, during the first decade of noise exposure, an improvement in hearing threshold levels (HTLs) was observed. The change in hearing over three measurements showed a concave development of hearing loss as a function of time, which corresponds to NIHL development.
Conclusions: Overall, hearing deteriorated over the measurement period. Because HTLs at follow-up were better than those obtained at baseline, no statement can be made about the NIHL development during the first decade of noise exposure. This improvement in HTLs rather resembles the result of measurement variation in occupational screening audiometry than an actual improvement in hearing ability.