Abstract
BACKGROUND:
Exposure to excessive noise is the most common preventable cause of hearing loss. It has been estimated that more than 12% of the global population is at risk for hearing loss from noise and about one-third of all cases can be attributed to noise exposure.
OBJECTIVES:
Data on occupational noise and its associated hearing loss are lacking in Jordan. This study aimed to determine the prevalence of noise induced hearing loss (NIHL) among industrial workers in Jordan.
METHODS:
This study included all workers who had been exposed to noise at least three years or more in three plants in Madaba Governorate in Jordan. A structured questionnaire was used to collect the data. The occupational noise was measured using a portable calibrated sound meter. Pure-tone air conduction audiometry was performed to determine the hearing thresholds in the frequencies of 250, 500, 1000, 2000, 3000, 4000, 6000, and 8000 Hz for both ears of all subjects
RESULTS:
This study included 196 workers aged between 20 and 54 years with a mean (SD) of 35.9 (7.2) year. Overall, the prevalence of NIHL among workers was 28.6% (35.0% among those exposed to high level of noise (>85 dB) and 12.5% among workers exposed to low level of noise (≤85 dB)). Age >35 years (OR = 2.7; 95% CI: 1.2–6.1), high noise level (OR = 4.2; 95% CI: 1.6–10.5), exposure of more than 10 years (OR = 2.0; 95% CI: 1.1–5.9), and not using hearing protective devices (OR = 2.7; 95% CI: 1.1–6.6) were significantly associated with increased odds of hearing loss.
CONCLUSIONS:
About one quarter of noise-exposed industrial workers in Jordan has NIHL. Age >35 years, high noise level, exposure of more than 10 years, and not using hearing protective devices were significantly associated with increased risk of NIHL.
Introduction
Occupational noise is one of most common occupational hazards that affect the hearing system and cause hearing loss after long exposure [1]. Exposure to noise might lead to psychosocial, physiological, and biochemical changes in the body [2–4]. The effect can be auditory, such as permanent or temporary hearing loss, and non-auditory like sleep interference, annoyance, loss of working efficiency and possible hypertension [5–7].
Exposure to excessive noise is the most common preventable cause of hearing loss. It has been estimated that more than 12% of the global population is at risk for hearing loss from noise [8] and about one-third of all cases can be attributed to noise exposure [9]. In the United States, the prevalence of hearing loss was reported as 23% among noise-exposed workers [10]. Moreover, a cross- sectional study of retrospective cohort analysis in USA in 2012 demonstrated that 18% of industrial workers had hearing loss [11].
The effect of noise on hearing loss depends exposure time, intensity and type of noise. Noise-induced hearing loss (NIHL) can be defined as a partial or complete hearing loss in one or both ears as the result of one’s employment. The National Institute for Occupational Safety and Health (NIOSH) recommends that a Recommended Exposure Limit (REL) for noise be 85 decibels (dB (A)) for 8 hour a day [12]. This standard is adopted by the Ministry of Health in Jordan. Data on occupational noise and its associated hearing loss are lacking in Jordan. This study was conducted to determine the prevalence of NIHL among plants workers in Jordan. Such data are necessary for planning control and preventive programs for workers.
Methods
Study design
A cross-sectional study was conducted in three plants in Madaba Governorate in Jordan. All industrial plants in Madaba (nine plants) were divided into three groups based on the number of workers: Two large plants with 100 workers or more, three medium plants with more than 50 workers and less than 100 workers, and four small plants with 50 workers or less. One plant from each group was randomly selected. The first one was a bottling plant with 138 workers. It consists of different sections including plastic line section, syrup treatment section, can bottling line section, glass bottled line, warehouse section, lab section, and maintenance section. The second plant was construction chemicals plant with a total of 98 workers. It consists of the following sections: mixing and compressor section, isolation material line (PVC) section, warehouse section, maintenance section, and lab section. The third plant was steel production plant (Iron scissor section, iron drill section, and blacksmith section).
Subjects
Plants were visited between January and April 2017 after obtaining the official approvals. The total number of all workers from three plants was 274. Workers who had been exposed to noise at least three years or more in these plants were invited to participate in this study. A total of 15 workers who had hearing problems before they started their job or had acute ear disease during the study were excluded from the study leaving a total of 196 workers to be included in the analysis. All invited workers agreed to participate in this study. All workers had fixed daytime shift (8.00am–4.00pm) and were working eight hours a day for six days per week with 30 minutes daily break. A consent form was obtained from all participants.
Data collection
Ethical approval was obtained from the Jordan Ministry of Health ethical committee. A structured questionnaire was used to collect data on socio-demographic characteristics of the participants, duration of exposure, difficulty in hearing, tobacco use, and use of protection equipment.
The participants underwent an otoscopic examination using Otoscope (KaWe® PICCOLIGHT® C Otoscope, Germany) and tympanometry. Pure-tone air conduction audiometry was performed to determine the hearing thresholds in the frequencies of 250, 500, 1000, 2000, 3000, 4000, 6000, and 8000 Hz for both ears of all subjects using an audiometer with earmuffs (GSI 61, Grason Stadler, Minneapolis, MN, USA). The measurement of hearing thresholds was done in 5 dB increments. The subjects were considered to have noise-induced hearing loss in either ear if an average threshold shift of over 25 dB at high frequencies of 3000, 4000, 6000, and 8000 Hz had been recorded. If an average threshold shift exceeded 25 dB at high frequency in both ears, the subjects had both ears hearing loss. Audiometry was performed at least 14 h after the last exposure to noise in the workplace. The subjects underwent audiometry before working to avoid the temporary threshold shift.
Noise level measurement
The occupational noise was measured by a well-trained technician from the Occupational Health Directorate of Jordan, using a portable calibrated sound meter (Casella CEL-450A series (Bedford, UK)). Exposure levels were estimated based on area noise monitoring for each individual worker in the study. Area monitoring for noise was completed with data obtained at locations that would be representative of the workers’ exposures.
Statistical analysis
Data were analyzed using the Statistical Package for Social Sciences (IBM SPSS) version 20. The Chi-square test was used to analyze the differences between proportions. Logistic regression analysis was used to determine the factors associated with NIHL. The odds ratio (OR) and 95% confidence intervals (95% CIs) were calculated. A P-value > 0.05 was considered statistically significant.
Results
Participant characteristics
This study included 196 workers aged between 20 and 54 years with a mean (SD) of 35.9 (7.2) year. About 63.8% of workers had been exposed 3 to 10 years to occupational noise in the studied industrial plants. Table 1 shows the demographic and relevant characteristics of participants. Workers were exposed to a mean (SD) noise level of 87.6 (6.6) dB in all plants. Of those, 56 (28.6%) workers were exposed to noise lower than NIOSH permissible limit (≤85 dB) and 140 (71.4%) were exposed to noise higher than permissible limit (>85 dB). About 46% of workers were not using hearing protective devises.
The demographic and characteristics of workers
The demographic and characteristics of workers
Overall, the prevalence of hearing loss among workers was 28.6% (21% in the right ear, 21.4% in the left ear, and 13.8% in both ears). Table 2 shows the prevalence of hearing loss according to socio-demographic characteristics’ and the level of noise exposure. The prevalence of hearing loss at frequency 4000 Hz was 35.0% among those exposed to high level of noise (>85 dB) and 12.5% among workers exposed to low level of noise (≤85 dB) (p-value = 0.002).
The prevalence of hearing loss according to demographic characteristics and the level of noise exposure
The prevalence of hearing loss according to demographic characteristics and the level of noise exposure
Table 3 shows the multivariate analysis of factors associated with hearing loss. Age >35 years, high noise level, exposure of more than 10 years, and not using hearing protective devices were significantly associated with increased odds of hearing loss. Those who aged more than 35 years had increased odds of hearing loss (OR = 2.7; 95% CI: 1.2–6.1) compared to workers aged 35 years or less. Exposure to high level of noise was significantly associated with increased odds of hearing loss by almost 4 folds (OR = 4.2; 95% CI: 1.6–10.5). Exposure to noise for a period of 10 years or more (OR = 2.0; 95% CI: 1.1–5.9) and not using hearing protective devices (OR = 2.7; 95% CI: 1.1–6.6) were more likely to have hearing loss.
Multivariate analysis of the factors associated with hearing loss
Multivariate analysis of the factors associated with hearing loss
NIHL is a prevalent occupational disease and is a major public health problem with economic consequences [13, 14]. It is particularly common in many occupations with exposure to high noise levels. This study showed a high rate of hearing loss among industrial workers in Jordan, especially among those who were exposed to high levels of noise. Exposure to a high level of noise >85 dB was associated with a three fold increased hearing loss compared to those who were exposed to low level of noise≤85 dB. It is difficult to compare the results of this study with findings of previous research because the criteria for NIHL varied from country to country and from study to another [15]. Regardless of the criteria used, many studies showed high prevalence rates of hearing loss among exposed groups [16, 17]. One study in India showed that 6 % of employees with daily noise exposure >90 dB and none of the controls had hearing loss [17]. In a longitudinal study, the hearing loss at 4 kHz in the Dutch construction workers ranged from 0 dB for the age group >25 years to about 7 dB for the 55–64 year group, compared with the internal control group [18]. The higher prevalence rate reported in this study might be attributable to poor implementation of control and preventive measures such as hearing protective devices. Almost half of participants reported no use of hearing protective devices.
Hearing protection devices have been used as a control measure for prevention NIHL. Our study showed that workers who did not use hearing protective devices were 2.7 (95% CI: 1.1–6.6) times more likely to have hearing loss compared to those who always use these devices. This finding is consistent with other previous studies [19, 20] that showed that the use of hearing protection may have a beneficial effect and some preventive effect. Nevertheless, such control measures are underused and often fail in the construction industry [21]. Groenewold et al. [22] showed a marginally significant difference for hearing shift between workers who reported rare versus frequent use of hearing protection devices. To ensure conservation of hearing health, awareness program should be implemented among workers exposed to occupational noise. A review study suggested that efforts should focus on measures to protect workers rather than on the control of the source of noise [23].
Our study showed that exposure to noise for a period of 10 years or more is associated with increased risk of hearing loss. A study in Denmark showed that the risk of hearing loss was tripled by exposure to noise for more than 20 years [24]. The objective risk of hearing damage was significantly higher for construction workers compared with controls (OR = 1.6, 95% CI = 1.3–2.1) and increased with the duration of time employment, although the confounding effect of other factors such as age and smoking was not ruled out [25].
The generalizability of the findings of this study might be limited because the study included only three industrial plants. Moreover, a definite cause-and-effect relationship cannot be established from this study that utilized cross-sectional design.
In conclusion, NIHL is highly prevalent among noise-exposed workers in Jordan. Age >35 years, high noise level, exposure of more than 10 years, and not using hearing protective devices were significantly associated with increased risk of hearing loss. Prevention efforts must be implemented in the work environment. Industrial implants should follow the legislation defining exposure limits. The actions taken to control NIHL are related to noise control. Establishing breaks, and rotating shifts through the noisy area, can be effective.
Conflict of interest
None to report.
Footnotes
Acknowledgments
Authors would like to acknowledge the Training Programs in Epidemiology & Public Health Interventions Network (TEPHINET) and Jordan Field Epidemiology Training Program for their technical support.