Noise and age-related hearing loss : a study of 40 123 gold miners in South Africa

Abstract

OBJECTIVE AND DESIGN : This retrospective cohort study aimed to describe the differential effect of noise exposure and age-related hearing loss in a large sample of gold miners in South Africa. STUDY SAMPLE : Audiological data of 40 123 South African mine workers were investigated. Data of a non-noise-exposed control group (n 6162) and group exposed to underground noise ( 85 dB A (TWA) (n 33 961) were included. Within these two larger noise-exposed groups two homogenous exposure groups (HEG) were also selected for analyses, namely the driller group (n 4399) and the administration group (administrative workers) (n 2211). Participants were categorized in terms of noise exposure, age, and race. RESULTS : Signifi cantly different thresholds (worse for underground noise group) with respect to the median for all frequencies after adjusting for age was evident between the noise-exposed and control groups (ANCOVA). The largest differences in hearing thresholds between the noise-exposed and control groups were observed at 3 and 4 kHz in the age group 36 to 45 years. Administration and driller group differed significantly (driller group worse results) with respect to the mean LFA512 and HFA346 after adjusting for age (ANCOVA). Black males had significantly better high-frequency hearing compared with white male counterparts but significantly worse low-frequency hearing. CONCLUSION : Age was the most important influence on hearing thresholds for the noise and control groups. Race was shown to be a very significant factor determining susceptibility to NIHL and ARHL.