Audiometric notch as a sign of noise induced hearing loss (NIHL) among the rice and market flour mill workers in Tamil Nadu, South India

Abstract

Objective

This study aims to determine the prevalence of NIHL among rice and flour mill workers exposed to high decibel noise levels at the workplace.

Methods

One-hundred and seven workers exposed to noise from rice and flour mill machinery and 82 age-matched controls not exposed to noise at the workplace were recruited for the study from the south Indian state of Tamil Nadu. All the mill workers and the controls were evaluated for their hearing thresholds by pure-tone audiometry.

Results

The characteristic bilateral notch in 4000 Hz was detected in 25% of the mill workers, while the prevalence of the unilateral or bilateral notch was observed in 51%. The high-frequency slope (HFS) involving HL at 4000 and 8000 Hz was observed in 23.36 and 29.92% among the left and right ears of the mill workers, respectively. Years of experience and exposure to noise were strongly associated with a bilateral notch in 4000 Hz (the odds of having the notch increased with increased years of noise exposure). Self-reported HL under-represented the rates of actual HL, indicating perception of the HL was absent till audiometric evaluation revealed the loss.

Conclusion

Our study demonstrates exposure to high noise levels in this unorganized sector of rice and flour mill workers. Awareness education of NIHL, early detection, and the use of personal hearing protection devices can prevent HL from extending to speech frequencies.

Keywords:

• Noise induced hearing loss
• rice/flour mill workers
• occupational hearing loss
• 4000 Hz notch

Acknowledgements

We are thankful to Prof. A. Govindaraju, Head, Department of Biostatistics, Chettinad Hospital, Chennai for his immense help with the statistical analysis. We wish to record our profound gratitude to Dr. N.P. Karthikeyan for editing the manuscript. We also wish to acknowledge the contributions of PG trainees who helped in ascertaining the samples. S.N. and C.J. were supported by UGC BSR. J.J.M. was supported by CSIR and DBT SRF.

Author contributions

C.R.S., R.R., and K.R. contributed to the conceptualization of this study and obtained funding. C.R.S., S.N., G.V., J.J.M., and C.J. recruited subjects for the study. S.N. and R.R. contributed to noise level assessments, clinical and audiometric evaluation. S.N., R.R., and C.R.S. prepared the original draft. C.R.S. and J.J.M. contributed to editing, review, and intellectual input to the final manuscript. All authors read and approved the final manuscript.

Disclosure statement

There is no conflict of interest between the authors. The authors are entirely responsible for the content and writing of this article.

Additional information

Funding

This study was supported by Tamil Nadu Pollution Control Board (TNPCB) TNPCB/1715/AR&D/D.D.(L)W/2013 research grant and UGC Research Scientist Scheme (F.8-17(SC)/90(SA-II)) Government of India, sanctioned to C.R.S.