Occupational Hearing Loss Associated With Non-Gaussian Noise: A Systematic Review and Meta-analysis.

Only seven of the 78 included studies followed workers over time; the rest took a single snapshot, so the link between job noise and hearing loss is an association and not proof of cause. The review used the Chinese definition of high-frequency hearing loss (an average threshold of 40 dB HL or more at 3, 4 and 6 kHz) as an inclusion criterion, so workers with milder high-frequency loss were left out and the pooled figures do not cover them. Too few included studies reported kurtosis for the effect of noise impulsiveness to be analysed properly. No included study looked at the relationship between noise exposure characteristics and speech-frequency hearing loss. Hearing protection use was usually not reported at all, and in the few studies where workers used it regularly it could have affected the hearing results. The pooled analyses are dominated by cross-sectional studies, and a few studies with regular hearing protection use could have pulled the estimates in either direction.

The review was funded by the Zhejiang Provincial Key Research and Development Project (2015C03039), the Zhejiang Provincial Program for the Cultivation of High-Level Innovative Health Talents, and the Health Commission of Zhejiang Province (2019KY057), all in China. The authors state there are no conflicts of interest, financial or otherwise.

Do not treat the kurtosis-adjusted cumulative exposure index as something you can use now. The review proposes it as a better way of judging risk, but too few of the included studies reported kurtosis for it to be tested, and the authors' own conclusion is that more studies are needed. Nor does this review show that any particular hearing protection programme or device prevents hearing loss; it reports how common hearing loss is among exposed workers, not what stops it.