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

Abstract

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.

Keywords: Annual audiometry; Hearing conservation; Occupational noise exposure; Occupational noise-induced hearing loss; Occupational surveillance frequency; Threshold shift.

Fig. 1

Calculation method of mean annual thresholds shift (gaps) in different time intervals between checkups

Fig. 2

Joinpoint trend analyses of mean annual threshold shifts among exposed (rectangles) and reference groups (circles and dashed trend lines) calculated according to consecutive time intervals of hearing checkups for participants aged below 50 years at entry

Fig. 3

Joinpoint trend analyses of annual threshold shifts variability, represented by coefficient of variation (standard deviation divided by mean) according to sequential time intervals for calculating ATS among noise-exposed workers aged below 50 years at entry. As the time interval between consecutive hearing checkups increased, the mean annual change (ATS) variability decreased, implying improved accuracy

Fig. 4

Mean annual threshold shifts calculated according to consecutive time intervals of hearing checkups in noise-exposed workers aged below 50 years at entry: newly exposed who had 0–3 years of service at baseline (N = 47), compared to senior workers who had more than 3 years of exposure at baseline (N = 127). Abbreviations: dB, decibel(s); ATS, annual threshold shifts. All T tests between newly exposed and veteran workers were non-significant (P > 0.05)