Noise-induced hearing loss in grass-trimming workers

Abstract EN

Introduction : Noise-induced hearing loss results from accumulated repetitive noise exposure of high amplitude.

Grass-trimming workers are exposed to a noisy motorized machine that is carried on their back.

We studied the prevalence of noise-induced hearing loss and its characteristics among the workers.

Methods : A comparative cross sectional study was conducted on a group of grass-trimming workers.

Ear examination was conducted, followed by pure tone audiometry in a soundproof room at least 48 h after the subjects were free from the noise exposure.

Noise-induced hearing loss was defined as failed definitive threshold at frequencies 3, 4 or 6 kHz of more than 20 dB with the loss at the two nearest frequencies on both sides of the dip amounting to at least 5 dB less.

The intensity levels of the grass-trimming machines were measured by using a sound level meter by putting the probe near the external ear of the worker about 12 cm apart from his pinna.

Results : A total of 75 grass-trimming workers and a similar number of clerks participated in this study.

The range of noise level of the machines was in between 91.3 dB and 100.7 dB with the mean of 95.0 dB.

There was a significant correlation of noise-induced hearing loss in the grass-trimming workers (p value = .010) with the prevalence of 82.6%.

The dip in PTA at 3, 4 and 6 kHz significantly occurred in the subjects with the p value of 0.001, 0.009 and 0.036 respectively.

Conclusion : It is warranted to give continuing education on the grass-trimming workers about the risk and how to protect them from noise-induced hearing loss.

While the diagnosis should be made in the presence of exposure, the possibility of noise-induced hearing loss is highest when the dip occurs at 3 kHz followed by 4 and 6 kHz