title: Evaluation of Distortion Product Otoacoustic Emissions (DPOAEs) among workers at an Industrial Company exposed to different industrial noise levels in 2014.
abstract: BACKGROUND
  Noise-induced hearing loss (NIHL) is usually one of the main problems in industrial settings. The aim of this study was to determine whether changes in the signal-to-noise ratio (SNR) in different DPOAE are caused by exposure to different levels of noise at different time intervals among workers exposed to noise.
  
  
  METHODS
  This case-control study was conducted in the autumn of 2014 on 45 workers at Gol Gohar Mining and Industrial Company, which is located in Sirjan in southeast Iran. The workers were divided into three groups based on their noise exposure, i.e., 1) 15 office workers as a control group with exposure to low levels of noise, 2) 15 workers from manufacturing departments who were exposed to a medium level of noise, and 3) 15 workers from manufacturing departments who were exposed to high levels of noise. The SNRs at the frequencies of 1000, 2000, 3000, 4000, and 6000 Hz were measured in both ears at three different time intervals during the shift work. SNRs of 6 or greater were considered as inclusion criterion. Repeated measures, the Spearman rank-order correlation test, and paired t-test analyses were used with α = 0.05 being the level of significance.
  
  
  RESULTS
  For all frequencies in the right and left ears, the SNR values were more than 6, thus all SNR values were considered as acceptable responses. The effects of time and sound pressure level (SPL) on SNR were significant for the right and left ears (p = 0.027 and < 0.001, respectively). There was a statistically significant correlation between the SNR values in the right and left ears for the time intervals 7:30-8:00 A.M. and 13:30-14:00 P.M., which implied that an increase in the duration of exposure led to reduced SNR values (p = 0.024, r = 0.948).
  
  
  CONCLUSIONS
  The comparison of the SNR values in the right and left ears (for all frequencies and the three different SPLs) indicated that the values decreased during the shift work.
authors.affiliation: Ph.D. Student, Department of Occupational Health, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Sajad
authors.initials: S
authors.lastname: Zare
authors.affiliation: Professor, Department of Occupational Health, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Parvin
authors.initials: P
authors.lastname: Nassiri
authors.affiliation: Professor, Department of Occupational Health, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Mohammad Reza
authors.initials: MR
authors.lastname: Monazzam
authors.affiliation: Associate Professor, Department of Audiology, School of Rehabilitation, Iran University of Medical Sciences, Tehran, Iran.
authors.forename: Akram
authors.initials: A
authors.lastname: Pourbakht
authors.affiliation: Associate Professor, Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Kamal
authors.initials: K
authors.lastname: Azam
authors.affiliation: Associate Professor, Department of Biochemistry, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Taghi
authors.initials: T
authors.lastname: Golmohammadi
keywords: hearing loss; noise-induced; otoacoustic emissions; signal-to-noise ratio