[Neurosensorial hearing loss caused by noises: results of a longitudinal study in iron and steel workers].

BACKGROUND

The detrimental effect of noise in the ear is well known. However, several countries debate the acceptance of hearing loss caused by exposure to noise as a professional disease.

AIM

To assess the association of noise levels in an industrial environment with neurosensorial hearing loss.

SUBJECTS AND METHODS

One thousands two hundred thirty two workers exposed to low, moderate and high noise levels were studied. All had a normal admission audiogram and at least one further audiogram.

RESULTS

Four hundred forty five subjects, aged 40.4 +/- 8.2 years old, were exposed to low environmental noise, 341 subjects, aged 39 +/- 7.8 years old were exposed to moderate noise and 446, aged 39.2 +/- 7.3 years old were exposed to high noise for 16.7 +/- 8.1, 14.8 +/- 7.7 and 15.2 +/- 7.6 years respectively. The prevalence of hearing loss was 7.2, 11.7 and 13.2% among those exposed to low, moderate or high environmental noise. According to our legislation 0.4, 1.5 and 2.5% of those workers had a hearing impairment entitled to compensation. The regression slope for hearing loss was 0.5, 0.7 and 0.8 dB/year of age in workers exposed to low, moderate and high noise levels respectively. A significant effect of noise was observed after the age of 40 in those exposed to high levels, and after the age of 50 in those exposed to moderate levels.

CONCLUSIONS

According to our safe noise exposure criteria, we are accepting that 18.2% of workers will suffer a disabling hearing loss at the end of their job life and that 0.4% will not attain an economic compensation in spite of their impairment.