Hearing threshold levels of Australian coal mine workers: a retrospective cross-sectional study of 64196 audiograms

The rate of occupational noise-induced hearing loss among male workers in Israel and implication on hearing surveillance frequency

OBJECTIVES

To investigate the annual rate of NIHL in Israel, a modern economy with relatively low industrial hazardous noise exposure. To review international protocols of hearing surveillance. To recommend an effective, efficient, hearing screening frequency protocol.

METHODS

A historical cohort study was conducted. Audiometric surveillance data from the Jerusalem occupational medicine registry of male employees in various industries from 2006 to 2017 were used. Mean individual annual threshold shifts simulating 1-8 checkup interval years were calculated. Joinpoint regression analysis was used to assess the interval in which the slope of the calculated ATS variability moderates significantly.

RESULTS

A total of 263 noise-exposed workers and 93 workers in the comparison group produced 1913 audiograms for analysis. Among the noise-exposed workers, using the 1-4 kHz average, threshold shifts stabilized from 3 years onwards at around 1 dB per year in all age groups and 0.83 dB in the stratum younger than 50 years. No enhanced decline was detected in the first years of exposure.

CONCLUSION

Although most countries conduct annual hearing surveillance, hearing threshold shifts of noise-exposed workers become more accurate and show less variability when calculated at 3-year checkup intervals onwards than shorter intervals. Since margins of errors of the test method are much larger than the annual shift found, screening schedule that enables each subsequent test to identify a real deterioration in hearing is necessary. Triennial audiometric screening would be a better surveillance frequency for noise-exposed workers younger than 50 years of age in the category of 85-95 dBL_Aeq,8 h without other known risk factors.

Pre-employment hearing threshold levels of 59,601 Australian male coal miners compared to an otologically normal international male population (ISO7029:2019)

OBJECTIVE

This study compared the pre-employment median hearing threshold level (HTL) distribution from a population of coal miners from New South Wales (NSW), Australia, to an otologically normal, age-matched population described by the International Standards Organisation (ISO) ISO 7029:2019, to determine any differences.

DESIGN

This was an observational, retrospective, repeated cross-sectional study.

STUDY SAMPLE

De-identified audiometric records of 59,601 male employees entering NSW coal mining in three representative five-year periods between 1991 and 2015 were utilised.

RESULTS

The median HTL deviation of the mining population was statistically significantly different (p < 0.05) from the ISO population, for almost all analyses. Overall, the mining population cohorts have higher (worse) median HTLs compared to the ISO population. The greatest difference occurs at 4 kHz in older age groups, likely indicating noise-induced hearing loss.

CONCLUSION

These findings indicate that some NSW coal mine workers commence their careers with evidence of pre-existing hearing loss (HL), in an industry with excessive noise exposures. These results provide Australian mining and other noisy industries with evidence to support a review of hearing conservation strategies to improve mitigation of hearing loss across the working lifespan.