The risk of noise-induced hearing loss in the Danish workforce

The causal association between occupational noise exposure and permanent hearing loss is well-documented and well-founded primary preventive approaches have been developed. However, documentation of the impact on the present prevalence of noise-induced hearing loss in the working population is limited. This study reports on the prevalence of noise-induced hearing loss in a population sample of 788 workers from 11 trades with expected high noise exposure levels and a reference group examined according to the same protocol. Full-shift A-weighted equivalent sound levels were recorded and pure tone audiometric examinations were conducted at the work sites in soundproof booths. Data were analyzed with multivariate regression techniques and adjusted for age, sex, ear disease, smoking and environmental noise exposure. An overall two-fold increased risk of hearing handicap (hearing threshold above 20 dB averaged across 2, 3 and 4 kHz for either ear) was observed in the noise exposed workers [odds ratio (OR) 1.99, 95% confidence interval (CI) 0.91-4.34]. Workers exposed for more than 20 years to an exposure level above 85 dB(A) had a three-fold increased risk (OR 3.05, 95% CI 1.33-6.99). Workers starting in noisy work during the last 10-15 years or workers below 30 years of age showed no increased risk of hearing handicap. This indicates that preventive measures enforced during the past 10-15 years to reduce noise exposure may have borne fruit. Systematic surveillance of noise and hearing levels in appropriate populations should still be included in an efficient hearing conservation program.