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Khoshakhlagh A H, Yazdanirad S, Sarsangi V. The Relationship between Individual Risk Factors and Hearing Loss in Textile Workers. AOH. 2018; 2 (2) :121-127
URL: http://aoh.ssu.ac.ir/article-1-73-en.html
1- Department of Occupational Health Engineering, Faculty of public Health, Tehran University of Medical Sciences, Tehran, Iran & Students’ Scientific Research Center, Tehran University of Medical Sciences, Tehran, Iran
2- Department of Occupational Health Engineering, Faculty of public Health, Tehran University of Medical Sciences, Tehran, Iran , saeedyazdanirad@gmail.com
3- Department of Occupational Health Engineering, Faculty of public Health, Tehran University of Medical Sciences, Tehran, Iran
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The Relationship between Individual Risk Factors and Hearing Loss in Textile Workers
Amir Hossein Khoshakhlagh1, Saeid Yazdanirad2*, Vali Sarsangi3
1Department of Occupational Health Engineering, Faculty of public Health, Tehran University of Medical Sciences, Tehran, Iran & Students’ Scientific Research Center, Tehran University of Medical Sciences, Tehran, Iran•2 Department of Occupational Health Engineering, Faculty of public Health, Tehran University of Medical Sciences, Tehran, Iran•3 Department of Occupational Health Engineering, Faculty of public Health, Tehran University of Medical Sciences, Tehran, Iran•Corresponding author: SaeidYazdanirad, Email:saeedyazdanirad@gmail.com, Tel: +98-913-4084163
Background: Noise-induced hearing loss (NIHL) is a debilitating and irreversible disease and one of the ten most important occupational diseases. The purpose of this study was to investigate the relationship between individual risk factors and NIHL in textile workers. Methods: This cross-sectional study was carried out on 128 employees of one of the textile factories of Tehran Province in 2017. At first, data were collected using a demographic questionnaire including age, marital status, level of education, and work shift. Then, using an audiometer, the workers' threshold of hearing was measured in both ears for frequencies of 500, 1000, 2000, 4000, and 8000 Hz, and data were analyzed by the SPSS version 18.Results:The mean age of the workers was 30.59 ( 3.5) years, their mean work experience 5.7 (2.76) years, and the mean environmental noise level at work 87.88 ( 6.13) dB. The findings showed that there was a significant relationship between the level of exposed noise and age, education level, work shift, and marital status. Conclusion: Increased age of population and level of environmental noise are two factors for increased hearing loss, which can be partly prevented by using engineering approaches such as using mufflers and silent rooms.
Keywords: Noise; Hearing loss; Audiometry; Important risk factors for hearing loss
he development of modern automatic machines in the industry has significantly reduced the physical load of workers, and, on the other hand, has increased the production and productivity of industrial enterprises. One of the undesirable and unavoidable byproducts of these operations and equipment is noise pollution. In most countries across the globe, the association between noise exposure and hearing loss is known. Following the Industrial Revolution, continuous noise was introduced into work environments and its influence on the workers' hearing system expanded.1
Long-term exposure to excessive noise without taking necessary precautions can have detrimental effects on the function of various parts of the body. These effects include hearing loss, mental disorders, reduced efficiency, and undesirable effects on the circulatory system.2-4 The biological basis for noise-induced hearing loss (NIHL) is a combination of mechanical and metabolic factors. Chronic exposure of cochlear hair cells to excessive noise and metabolic changes due to hypoxia caused by contraction of blood capillaries as a result of exposure to noise can lead to hearing loss.5,6 NIHL is one of the most commonly occurring work-related illnesses in the world, so that it is among the 10 leading occupational diseases in Canada and the United States.7,8
Noise-induced damage to the hearing system can occur as three ear diseases, i.e., NIHL, acoustic trauma, and tinnitus. Hearing loss is divided into two types, temporary threshold shift (TTS) and permanent threshold shift (PTS).9 PTS is caused by the destruction of the hair cells of the Organ of Corti and is often irreversible.10 To make definite diagnosis of hearing loss, pure-tone audiometry must be used (7, 8). Increased threshold of hearing in audiometry in people exposed to noise can indicate damage to their cochlea.11 So far, different statistics have been published that reveal that occupational exposure to this detrimental factor is widespread in the employees of different occupations. Occupational Safety and Health Administration (OSHA) has estimated that over 7.9 million industrial workers in the United States are exposed to over 80 dB noise due to their work.12 On the other hand, according to estimates by the Environmental Protection Agency (EPA), more than 9 million US workers in industry sectors are exposed to noise levels of, or exceeding,
80 dB.12
According to the OSHA, the National Institute on Deafness and Other Communication Disorders (NIDCD), and the American Speech-Language-
Hearing Association (ASHA), more than 30-40 million Americans are regularly exposed to hazardous levels of noise. Occupational NIHL is estimated to have affected 10-15 million people in all age groups in the United States.13,14 One fourth of workers who have the history of exposure to sound levels exceeding 90 dB during their working lives will develop hearing loss due to occupational noise exposure.12 In Sweden, about 9% of all workforces are continuously introducing into exposure to a hazardous noise level, and NIHL is very costly so that roughly 100 million dollars is paid annually to compensate for the disease in the country; the Canadian compensation board has estimated the mean cost paid for hearing loss claim 14000 Canadian dollars.15
In the United States, compensation for hearing loss claim in 1990 was estimated to be roughly 200 million dollars.16 In Greece, in 2001, 10% of the burden of occupational disease was due to noise exposure.17 A number of studies in recent decades have been conducted to evaluate the occupational environment in industries. Most of these studies have been carried out in developed countries, while a large part of industries causing high levels of noise, such as the textile industry, across the world have been established in developing countries.15 Hearing loss caused by exposure to high levels of noise is dependent on various factors such as exposure duration, frequency, and level and type (continuous or percussion) of sound. On the other hand, there are a number of demographic characteristics that may have a direct or indirect effect on NIHL. Considering the importance of this issue and also considering that the textile industry is an important industry in terms of noise exposure, this study was conducted to investigate the relationship between individual risk factors and NIHL in textile workers.
In this cross-sectional study, the hearing status of 128 workers in a textile factory in Tehran Province in 2017 was investigated. For sampling, all people who had exposure to high levels of noise were included in the study. All workers worked 8 hours a day, 5 days a week. Inclusion criterion was exposure to noise level above 85 dB. To control confounding factors, the people with temporary threshold shift (TTS), job change, exposure to toxins affecting the sensor neural hearing loss such as mercury, lead, cobalt, and urea, and the use of drugs that affect the mechanism of hearing such as desferrioxamine, salicylates, quinines, mandelamine, aminoglycosides, and antibiotics and diuretics affecting the loop of Henle (Furosemide and Adrien) were excluded from the study as confounders.7
Then, people who were eligible to participate in the study were invited to the factory’s Occupational Health Care Unit to undergo the audiometry. Before the study, the stages of the study were explained to them and then they signed written consent to participate in the study. Before performing the audiometry, demographic data including age, work experience, job type, work shift, and education level were collected by using a questionnaire. To perform the audiometry, pure-tone audiometry was used. To this end, ear of people with earwax was washed. Audiometry was then performed through air conduction at frequencies from 500-8000 Hz.
Audiometry was performed in a quiet audiometric test room (40 dB) and both ears of the workers were examined for NIHL by an eligible audiologist using an audiometer (Belton 2000 Clinical Audiometer) at frequencies of 500, 1000, 2000, 3000, 4000, 6000, and 8000 Hz according to a scientific method.7 The workers' audiometric baseline information was collected from their medical records. According to the OSHA, if the average difference observed between the last audiogram and baseline audiogram at the frequencies of 2000, 3000, and 4000 Hz is at least 10 dB in either ear, hearing threshold shift has occurred (18). Then, workers were classified based on the type of job‌ and the noise level that each group of workers with the same job had exposure to, was measured by dosimeter and average logarithmic values were calculated to determine their exposure.1.17 In addition, in the workers using hearing protectors, the effective noise reduction of the phone (50% of the tagged value of the noise reduction ratio (NRR) was deducted from noise exposure measured by the dosimeter. Finally, after data were entered in the SPSS version 18, ANOVA, the LSD, and t-test were used for data analysis. The significance level in the study was considered 0.05.
The measures of central tendency and dispersion of demographic characteristics and NIHL in the participants are shown in Table 1. In the factory, the workers had an average noise exposure of 87.88 (6.13)dB. The mean hearing loss of the left and right ear was 18.22 )11.91) dB and 19.51 (11.18) dB, respectively. The one-way ANOVA results of NIHL in different age groups were significantly different
(P = 0.001).
The results on variables such as job type, education level, environmental noise level, work shift, and marital status indicated that there was a significant relationship between each of the variables and occupational NIHL, while the work experience of individuals did not have any significant relationship with NIHL. The significance level between different demographic groups is shown in Table 2. The results of the LSD showed a significant difference in average hearing loss between group 3 and groups 1 and 2. The results also showed that there was a significant difference in NIHL between the ring operator and other operators and workers. The rate of hearing loss was significantly different between people with education levels lower than high school diploma and those with high school diploma and bachelor's degree. The difference in hearing loss between the people working in morning shifts and those in rotating shifts was significant. The rates of hearing loss for the various frequencies in single and married people are shown in Table 3.

Table 1.Measures of central tendency and dispersion of demographic characteristics and noise-induced hearing loss in participants
Variable Group no. Group Frequency Percentage Mean noise-induced hearing loss Standard deviation
Age (yr) 1 22-29 54 42.2 15.84 8.87
2 30-34 55 42.96 15.56 9.79
3 Over 35 19 14.84 25.35 11.59
Education level 1 Under high school diploma 56 43.75 19.78 11.12
2 High school diploma 67 52.34 15.64 9.03
3 Associate’s degree and bachelor’s degree 5 3.91 7.58 4.87
Work experience (yr) 1 1-4 41 32.03 16.49 9.73
2 5-9 65 50.78 16.96 9.77
3 Over 9 22 17.18 18.87 12.55
Type of job 1 Ring operator 36 28.10 23.48 9.12
2 Doubling machines Operator, etc. 36 28.10 19.18 10.32
3 Other jobs 56 43.80 11.74 7.87
Marital status 1 Single 17 13.28 12.00 5.82
2 Married 111 86.72 17.92 10.54
Work shifts 1 Morning shift 12 9.37 5.92 3.40
2 Afternoon shift 2 1.50 10.31 3.90
3 Rotating shift 107 83.60 18.75 10.13
4 Morning and afternoon shift 7 5.46 13.72 6.98
Table 2.Significance levels of differences among different demographic categories
Parameters I J Mean difference between I and J groups P-Value (significance level) 95% confidence interval
Lower limit Upper limit
Age group 1 2 0.30359 0.871 -3.3771 3.9843
3 -9.48668 0.000 -14.6115 -4.3618
2 1 -0.30359 0.871 -3.9843 3.3771
3 -9.79027 0.000 -14.9030 -4.6776
3 1 9.48668 0.000 4.3618 14.6115
2 9.79027 0.000 4.6776 14.9030
Job group 1 2 4.3056 0.044 0.1214 8.489
3 11.7411 0.000 7.948 15.533
2 1 -4.3056 0.044 -8.489 -0.1214
3 7.4355 0.000 3.643 11.227
3 1 -11.7411 0.000 -15.533 -7.948
2 -7.4355 0.000 -11.227 -3.643
Education level 1 2 4.14429 0.023 0.5916 7.6970
3 12.20461 0.009 3.0461 21.3631
2 1 -4.14429 0.0023 -7.6970 -0.5916
3 8.06032 0.082 -1.0363 17.1570
3 1 -12.20461 0.009 -21.363 -3.046
2 -8.06032 0.082 -17.107 1.0363
Work shift 1 2 -4.392 0.548 -18.837 10.052
3 -12.831 0.000 -18.589 -7.074
4 -7.8001 0.089 -16.795 1.194
2   4.392 0.548 -10.052 18.837
3 -8.439 0.218 -21.937 0.058
4 -3.407 0.657 -18.572 11.756
3 1 12.831 0.000 7.074- 18.589
2 8.439 0.218 -5..58 21.93
4 5.031 0.180 -2.346 12.41104
4 1 7.8001 0.089 -1.194 16.795
2 3.4077 0.657 -11.756 18.572
3 -5.0317 0.180 -12.410 2.346

Table 3.The rates of hearing loss for various frequencies in single and married people
  Frequency Mean Standard deviation 95% confidence interval (CI) Minimum Maximum
Lower limit Upper limit
Hearing loss in the right ear at 500 Hz Single 17 18.2353 10.14599 13.0187 23.4519 5.00 40.00
Married 111 26.2162 13.57163 23.6634 28.7691 5.00 55.00
Total 128 25.1563 1341256 22.8103 27.5022 5.00 55.00
Hearing loss in the right ear at 1000 Hz Single 17 18.2353 9.83317 23.2910 23.2910 5.00 35.00
Married 111 24.6847 22.1890 27.1804 27.1804 0.00 65.00
Total 128 23.8281 21.5511 26.1051 26.1015 0.00 65.00
Hearing loss in the right ear at 2000 Hz Single 17 11.4706 7.65766 7.5334 15.4078 0.00 25.00
Married 111 16.3514 11.88861 14.1151 18.5876 0.00 55.00
Total 128 15.7031 11.51402 13.6893 17.7170 0.00 55.00
Hearing loss in the right ear at 4000 Hz Single 17 8.8235 6.00245 5.7374 11.9097 0.00 20.00
Married 111 14.0541 12.44750 11.7070 16.4011 0.00 60.00
Total 128 13.3594 11.93996 11.2710 15.4477 0.00 60.00
Hearing loss in the right ear at 8000 Hz Single 17 7.9412 6.38818 4.6567 11.2257 0.00 25.00
Married 111 12.3423 11.88620 10.1065 14.5781 0.00 75.00
Total 128 11.7578 11.39122 9.7654 13.7502 0.00 75.00
Hearing loss in the left ear at 500 Hz Single 17 13.5294 6.31583 10.2821 16.7767 5.00 25.00
Married 111 22.6577 13.81402 20.0592 25.2561 5.00 65.00
Total 128 21.4453 13.41571 19.0988 23.7913 5.00 65.00
Hearing loss in the left ear at 1000 Hz Single 17 17.6471 11.33546 11.8189 23.4752 5.00 50.00
Married 111 23.2432 14.43872 20.5273 25.9592 0.00 70.00
Total 128 22.5000 14.15605 20.0240 24.9760 0.00 70.00
Hearing loss in the left ear at 2000 Hz Single 17 10.8824 11.62370 4.9060 16.8587 0.00 50.00
Married 111 16.1712 12.61231 13.7988 18.5436 0.00 60.00
Total 128 15.4688 12.57165 13.2699 17.6676 0.00 60.00
Hearing loss in the left ear at 4000 Hz Single 17 8.2353 7.05806 4.6064 11.8642 0.00 30.00
Married 111 14.2793 13.20893 11.7947 16.7639 0.00 70.00
Total 128 13.4766 12.71366 11.2529 15.7002 0.00 70.00
Hearing loss in the left ear at 8000 Hz Single 17 7.9412 6.62826 4.5332 11.3491 0.00 25.00
Married 111 13.7387 12.23758 11.4368 16.0406 0.00 60.00
Total 1287 12.9688 11.79613 10.9056 15.0319 0.00 60.00
Table 4.The results of regression analysis of the effect of different variables on hearing loss
Model Unstandardized coefficients Standardized coefficients t Significance level
B coefficient Standard error coefficient B
1 - -71.210 10.443 - -6.819 0.000
  Noise level 1.005 0.119 0.603 8.480 0.000
2 - -78.008 10.110 - -7.716 0.000
  Noise level 1.011 0.113 0.606 8.953 0.000
  Age group 3.660 0.980 0.253 3.736 0.000
3 - -48.011 12.991 - -3.696 0.000
  Noise level 0.741 0.133 0.444 5.560 0.000
  Nominal group 4.305 0.957 0.297 4.497 0.000
  Job group -3.435 0.991 -0.281 -3.467 0.001
4 - -33.478 14.011 - -2.389 0.018
  Noise level 0.654 0.135 0.392 4.841 0.000
  Age group 4.363 0.938 0.301 4.649 0.000
  Job group -3.695 0.976 -0.302 -3.784 0.000
  Education level -2.446 0.985 -0.164 -2.482 0.014
The coefficients and factors affecting each variable relative to hearing loss, which were derived from the

regression analysis, are shown as equation below.
(Job group ) -3.695 (Education level ) -2.446 (Age group ) +4.363 (Noise level ) +0.654 -33.478 Noise-induced hearing loss=
The results of the regression analysis of the effect of different variables on hearing loss are shown in Table 4. The results of the t-test showed that there was no significant difference in hearing loss between the left ear and the right ear. In addition, the regression analysis showed that the effect of noise level on hearing loss was greater than those of other variables, and then age had the greatest impact on hearing loss followed by the type of job and education level.
The environment of textile factories is conventionally associated with high noise levels so that noise level is often more than 110 dB in some units. In the present study, a significant relationship was observed between age and hearing loss. Significant relationship between age and hearing loss as well as between occupational environment noise level and NIHL is consistent with the results of a study by Hang et al. in Korea (2001). In this study, the relationship between these variables and NIHL was investigated by using multivariate statistical analysis.19Another study by et al. (2001) to investigate the effect of age variables, exposure to high noise levels, and other risk factors on NIHL, showed direct correlations of NIHL with noise level in work environment and age.20
The results of study in 535 metal workers (2005) also showed a direct correlation between age and exposure to high levels of noise in work environment, which are two important factors for occupational NIHL.21 This is consistent with our results. Meanwhile, the study of indicated that smoking effect was exacerbated by these factors. Age is considered a major risk factor for hearing loss in the elderly.
Age-related changes may have adverse impacts on nerve fibers, blood supply to nerve fibers in the brain, and inner and outer hair cells, and lead to progressive defects.22 These results are also in agreement with the results of a 4-year study by in the United States.23 The current study also showed that with increasing the noise level of the work environment, hearing loss increased. The results of et al.'s investigations in different industries showed a significant, direct correlation between work environment noise level and the severity of occupational NIHL.24 The study of the Barba in Brazil also showed a significant relationship between noise level and standard threshold change.25
The results of our study are consistent with the results of these studies. In addition, the results of the present study showed that there was a significant relationship between hearing loss and work shift so that hearing loss in people working in circulating shifts was higher, which may be due to the fact that these people have less time to rest and repair because people working in rotating shifts may have sleep disorders and problems. The rate of hearing loss was higher in married people than in single people.
Married people may be more exposed to noise due to more social and economic activities, even outside their original work shift, than single people. According to the findings, the lowest hearing loss was observed in those with an associate's degree and higher education levels.
This suggests that people with higher education levels use hearing protectors more frequently to protect their hearing system because they have a better understanding of the adverse effects of noise on hearing loss. On the other hand, the people with higher education level often work in higher-level occupations, which causes them to be exposed to noise for comparatively less time. In the present study, although people with higher work experience were found to have higher hearing loss, there was no significant relationship between work experience and the amount of threshold of hearing, which is consistent with the results of Barba.25 However, the results of Osibogun et al. showed that threshold of hearing in the people exposed to noise increased with increasing their work experience.26 This observation can be attributed to the fact that, often hearing loss begins in the first decade of employment, and people who have not experienced significant changes in their threshold of hearing during this period are unlikely to develop hearing loss in the long term. Workers may also have used hearing loss protectors to prevent the progression of hearing loss due to observing mild adverse effects of noise during the initial years of their work.
The results of this study showed that there was a significant relationship between hearing loss and demographic factors such as age, noise level, marital status, education level, and work shift. This information can be used to prioritize the control of noise in the work environment of people who are predisposed to hearing loss, or to transfer them from noisy occupational environments to the occupations with comparatively less noise exposure.
Conflict of interest
The authors declare no conflict of interest.
The authors appreciate the workers who participated in this study.
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Type of Study: Research | Subject: General
Received: 2018/04/8 | Accepted: 2018/04/8 | Published: 2018/04/8

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