Objectives Noise-induced hearing loss (NIHL) is the most prevalent occupational disease in Austria and among the most frequent in many other countries. Because of the large inter-individual variation in hearing loss after equal exposures it has long been assumed that some individuals are more vulnerable to NIHL. Earlier attempts to define predictors of NIHL before commencing occupational noise exposure have largely failed. From a preventive point of view it would be essential to study predictive factors.
Method Between 1982 and 1989 overall 311 apprentices were included into a prospective study during their initial health screening visit. At this occasion a standardised noise exposure was applied (20 min 200–500 Hz, 100 dBA) and the temporal threshold shift (TTS) at 4 kHz was determined during 2–10 min after exposure. Hearing loss was monitored at follow-up visits every 3–5 years. Follow-up was 13 years on average. Permanent threshold shift was predicted by noise years, frequency of wearing noise protectors, but also by the initial TTS at 4 kHz.
Results In this longitudinal study again the importance of personal protective measures was documented, it was also established that individual susceptibility plays an important role. The TTS peak at 4 kHz occurring independent of exposure frequency but especially after low-frequency exposure is a predictor of long-term hearing loss.
Conclusions Considering the importance of individual susceptibility current occupational limit values are likely not protective for everybody. This underlines the necessity of individualised screening programs and a strong commitment towards personal protection measures.
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