Effects of combined exposure to organic solvents and noise on hearing loss: A meta-analysis

Background Noise-induced hearing loss has become one of the most common occupational diseases in the world. However, the mechanism of hearing loss is very complex. Organic solvents as one of the ototoxic poisons have been confirmed to combine noise exposure to enhance hearing damage in working populations.

Objective The meta-analysis investigates the effects of combined exposure to organic solvents and occupational noise and individual exposure to occupational noise on hearing loss and the increased risks.

Methods By searching China National Knowledge Network (CNKI), Chinese Biomedical Literature (CBM), Wanfang, VIP, Medline, and Pubmed databases, domestic and foreign literature on the effects of combined exposure to organic solvents and occupational noise on hearing loss before January 2020 were retrieved. Cross-sectional studies were evaluated using the Agency for Healthcare Research and Quality (AHRQ) evaluation tool, and case-control studies and cohort studies using the Newcastle-Ottawa Scale. Effect values and supplement data included in the literature were analyzed using STATA 16.0. After heterogeneity analysis, a random effect model was used to merge the effect values. Sensitivity analysis and publication bias analysis were conducted for the included literatures, and meta-regression analysis and cumulative meta-analysis were conducted for the confounding factors in the included literatures.

Results A total of 19 high-quality papers were included in this study after the evaluation by AHRQ and NOS scales, and a total of 9 389 subjects were provided with information. There was heterogeneity (Q=110.11, P < 0.005, I²=84.16%). After adjustment, the odds ratio of hearing loss due to combined exposure to organic solvents and noise to noise exposure alone was 2.32 (95% CI: 1.75-3.07). The results of meta-regression analysis showed that independent variables such as organic solvent exposure concentration, exposure time, publication year, age, and noise intensity showed no statistical significance and sample size was the only contributor. Based on the results of cumulative meta-analysis, this heterogeneity did not change with the accumulation of publication time. The effect size OR was stable after sensitivity analysis, and there was no publication bias in the included literatures tested by Egger and Begg (Z=0.10, P=0.92; t=0.05, P=0.97).

Conclusion Based on the meta-analysis results of existing data, it is believed that combined exposure to noise and organic solvents increases the risk of hearing loss compared with exposure to noise alone.