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Five-Year Longitudinal Cohort Study Determines the Critical Intervals for Periodic Audiometric Testing Based on 5070 Tests of Workers Exposed and Non-Exposed to Noise

Background: Workers exposed to noise undergo periodic audiometric testing for early detection of hearing loss, but the optimal frequency of occupational audiometric tests remains unclear. We compared the progression of 3-, 4-, and 6-kHz thresholds over 5 years and determined the most critical period for occupational risk among workers exposed and non-exposed to noise. 
 
Methods: Metallurgy workers were divided into 2 groups: noise-exposed and non-noise-exposed groups. The 6 initial audiometric tests of each worker were analyzed as baseline test and periodic tests 1 to 5. 
 
Findings: A total of 845 workers were included, 748 in the noise-exposed group and 97 in the non-noise-exposed group, resulting in 5070 tests analyzed. The non-exposed group showed no significant difference in auditory thresholds between any of the periodic tests in either ear. In the exposed group, a significant difference was observed in auditory thresholds between baseline and Test1 (p=0.001 right ear; p=0.000 left ear), between Test3 and Test4 (p=0.002 right ear; p=0.005 left ear), and between Test4 and Test5 (p=0.003 right ear; p=0.000 left ear). There was no difference between Test1 and Test2 or between Test2 and Test3 in either ear. 
 
Interpretation: The progression of mean audiometric thresholds at 3, 4, and 6 kHz differed between workers exposed and non-exposed to noise. Noise-exposed workers had a significant progressive worsening of audiometric thresholds after 3 years of employment. Two critical periods of noise exposure were identified: in the first year and after the third year of employment in a noisy environment. 
 
Funding Statement: None. 
 
Declaration of Interests: The authors have no conflicts of interest to disclose. 
 
Ethics Approval Statement: This study was approved by the Institutional Review Board of the University of Campinas (0810.0.146.000-11).