Effect of Noise Exposure on 1,382 Metallurgical Workers in Periodic Audiometric Evaluation: A Cohort Study

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Abstract
Introduction: Noise-induced hearing loss is the most preventable cause of auditory impairment. Periodic audiometric evaluations are essential to monitor the hearing health of noise-exposed workers. Objective: To compare the evolution of audiometric thresholds in the initial three evaluations at frequencies of 3, 4, and 6 kHz in groups of workers exposed or not to noise. Methods: In this historical cohort study, audiometric evaluations were obtained from male workers between 18 and 40 years of age at six different metallurgical companies in Brazil. The workers were separated into noise-exposed and non-noise-exposed groups. The mean thresholds for 3, 4, and 6 kHz were calculated for both ears at baseline and the first and second periodic evaluations. The non-parametric Wilcoxon test was used for statistical analysis. Results: A total of 1,382 metallurgical workers were evaluated (1,199 noise-exposed and 183 non-noise-exposed). There was a significant difference between baseline and the first periodic evaluation (right ear – effect size = 0.62; p = 0.0030 and left ear – effect size = 0.74; p = 0.0063) and between baseline and the second periodic evaluation (right ear – effect size = 0.85; p = 0.004 and left ear – effect size = 0.96; p = 0.0002). In the non-noise-exposed group, there was no difference between baseline and the first periodic evaluation (right ear – effect size = 0.18; p = 0.2703 and left ear – effect size = 0.12; p = 0.7907) and between baseline and the second periodic evaluation (right ear – effect size = 0.29; p = 0.4475 and left ear – effect size = 0.41; p = 0.6381). Conclusion: In noise-exposed workers, there was a significant worsening of audiometric thresholds between baseline and the initial periodic evaluation, but there was no difference between the two post-baseline evaluations. This shows that noise exposure can quickly affect hearing, despite protective measures.

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