Effect of Noise Exposure on 1,382 Metallurgical Workers in Periodic Audiometric Evaluation: A Cohort
Vagner Antonio Rodrigues Silva, Alexandre Caixeta Guimarães, Joel Lavinsky, Henrique Furlan Pauna, Arthur Menino Castilho, Agrício Nubiato Crespo.
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 noiseexposed 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 nonparametric 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 noiseexposed 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.
Noise-induced hearing loss (NIHL), the most preventable cause of auditory impairment, is responsible for 16% of disabling hearing loss in adults [Frederiksen et al., 2017; Le et al., 2017; Lie et al., 2016; McBride and Williams, 2001]. Despite preventive regulations and workplace interventions, NIHL is still the second most common occupational disease [Frederiksen et al., 2017; Le et al., 2017]. NIHL is irreversible [Frederiksen et al., 2017; Imam and Hannan, 2017; Kerr et al., 2017], manifests initially at the frequencies of 3, 4, and 6 kHz [Coles et al., 2000] and extends to adjacent frequencies as it progresses [Coles et al., 2000; Duarte et al., 2015; McBride and Williams, 2001]. It rarely leads to profound hearing loss, since it usually does not exceed 40 dB of hearing loss at low frequencies or 75 dB of hearing loss at high frequencies. Once noise exposure ceases, NIHL does not progress [Imam and Hannan, 2017; Le et al., 2017]. Periodic audiometric evaluations are essential for monitoring the hearing health of noise-exposed workers. An increase in audiometric thresholds over time could indicate that the hearing conservation measures implemented by a company have not been effective [Leshchinsky, 2018]. The present study aims to compare the progression of mean audiometric thresholds of 3, 4, and 6 kHz among metallurgical workers in the initial three worker examinations. This study also aims to assess the effects of hearing conservation measures on noise-exposed workers during the first 2 years on the job according to the mean increase in audiometric threshold at 3, 4, and 6 kHz.
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