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Year : 2020  |  Volume : 26  |  Issue : 3  |  Page : 173-178

Hearing loss among cement factory workers in Northwest Nigeria

Department of Ear, Nose and Throat.Usmanu Danfodiyo University Teaching Hospital, Sokoto, Nigeria

Date of Submission16-Jan-2020
Date of Decision17-Feb-2020
Date of Acceptance08-May-2020
Date of Web Publication22-Dec-2020

Correspondence Address:
Dr. Nasiru Aliyu
Department of Ear, Nose and Throat,Usmanu Danfodiyo University Teaching Hospital Sokoto
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/indianjotol.INDIANJOTOL_9_20

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Background: Exposure to noise has been observed to have deleterious effect on the health status of individuals working within the noisy environment. Continuous exposure to high and unwarranted sound remains a major cause of hearing disorder all over the world. Occupational noise-induced hearing loss (NIHL) constitutes a worldwide problem in industries and contributes about 16% of hearing loss among adults globally. Aims and Objectives: The aim and objective was to evaluate the impact of occupational noise exposure on the auditory performance of workers at a cement company. Methods: This was a cross-sectional descriptive study of consenting workers at a cement company (public liability company). A total of 341 respondents were recruited for the study with equal number of controls matched for age and sex. Ear examination was done and based on the exclusion criteria, 23 participants with diseased ears were excluded. There hundred and eighteen participants (616 for both study group and control group) each had an interviewer–administered, semi-structured questionnaire and underwent diagnostic pure-tone audiometry. A digital sound level meter (Type 2 well-calibrated TOMTOP-Model Number H4320) with a range of 30–130 dB was used to map out the sound in the respective departments. Results: One hundred and one (31.8%) noise-exposed workers had mild (23.3%), moderate (7.2%), and severe (1.3%) hearing loss in their right ears as against the 21 (6.6%) in the controls. This was found to be statistically significant (P = 0.000). Seventy-seven (24.2%) noise-exposed workers also had mild (17.9%), moderate (6.0%), to severe (0.3%) sensorineural hearing loss in the left ear with the controls having 6.3%; this was also found to be statistically significant (P = 0.000). The presence of notch at 4 kHz audiometric configuration was 14.5% and 17% in better and worse ears, respectively. Three hundred (94.3%) workers in the noise exposed group worked for <8 h in a day (40 h/week) irrespective of the intensity of noise they were exposed to. Conclusion: This study has revealed a high prevalence of sensorineural hearing loss in the factory. This pattern of sensorineural hearing loss, coupled with the significant presence of 4 kHz audiometric notch among the noise-exposed workers (16.9%) in the worse ear when compared with the controls (3.1%) in the worse ear, strengthened the assertion that the hearing loss of the workers was likely attributable to occupational NIHL.

Keywords: Cement workers, hearing threshold, occupational noise exposure, pure-tone audiometry

How to cite this article:
Aliyu N, Iseh KR, Mohammed A, Yikawe SS, Inoh MI, Manya C. Hearing loss among cement factory workers in Northwest Nigeria. Indian J Otol 2020;26:173-8

How to cite this URL:
Aliyu N, Iseh KR, Mohammed A, Yikawe SS, Inoh MI, Manya C. Hearing loss among cement factory workers in Northwest Nigeria. Indian J Otol [serial online] 2020 [cited 2021 Apr 20];26:173-8. Available from: https://www.indianjotol.org/text.asp?2020/26/3/173/304291

  Introduction Top

Noise is the most common physical hazard in industrial workplaces.[1] Noise is defined as a sound especially one that is loud, is unpleasant, or causes disturbance.[2],[3] Exposure to noise has been observed to have deleterious effect on the health status of individuals working within the noisy environment; continuous exposure to this high and unwarranted sound remains a major cause of hearing disorder all over the world.[4] Occupational noise-induced hearing loss (NIHL) is a worldwide problem in the industry and on an average contributes 16% of hearing loss among adults globally, ranging from 7% to 21% in various subregions and higher in developing countries.[5],[6] In a study conducted in Ashaka Cement Company North East Nigeria, Ali et al. noted mild and moderate sensorineural hearing loss of 67.1% and 11.8%, respectively.[2] A similar study conducted by Ologe et al. in a steel-rolling mill in Nigeria documented a prevalence of 28.2% of the study population having mild-to-moderate sensorineural hearing loss in better ears.[7] Other studies conducted in Southwest Nigeria revealed a prevalence of 17% disabling hearing loss among two industrial workers in Lagos Nigeria,[8] 62.5% among spice grinders in Lagos,[9] and 71% among spice grinders in Ibadan.[10]

Quarrying is one of the major activities in producing minerals (i.e., rock and sands) for building infrastructures. The main activities of quarries involve granite blasting, crushing granites into smaller rocks, and converting it to asphalt.[11] The main contributory noise comes from the granite crushers, besides sounds from engine of excavators, dumping trucks, and lorries, which are also considered as sources of noise.[12] Occupational NIHL has resulted in human and economic consequences worldwide. The economic losses are also substantial and could be divided into direct and indirect cost.[13] Direct costs are relatively easy to estimate and mainly consist of medical examinations, compensations due to occupational diseases, and hearing protectors.[13] Indirect costs, on the other hand, are much more difficult to estimate. Occupational noise-induced hearing impairment is hardly a matter of public health concern in many developing countries including Nigeria. Again, developing countries often lack effective legislation against noise. Where this exists, it is often poorly enforced and implemented. The protection of health and safety of the workforce from hazards related to work activities is imperative and underpins a health and vibrant economy of any country. Therefore, this research work is aimed at evaluating the impact of occupational noise on the auditory performance of workers at Sokoto Cement Company (public liability company [PLC]).

  Materials and Methods Top

This was a prospective, cross-sectional, descriptive study conducted among workers of a cement company (PLC). The study population was categorized into noise-exposed participants (participants) and nonnoise-exposed participants, which were taken as the control group (mainly from the administrative block of the company and our university teaching hospital). The sample size was calculated to be 341 for the study group and an equal number of participants for the control group. Participants <18 years of age, those with evidence of hearing impairment before starting work at Sokoto Cement factory, those with ear disease, those with systemic illnesses, and nonpermanent staff were excluded from the study. The approval of management of the cement company and the ethical committee of our university teaching hospital was obtained.

A pretested questionnaire was used to obtain details about patients' biodata and medical history. A digital sound-level meter (Type 2 well calibrated Tomtop By Smart Sensor Inc., Houston US) with a range of 30–130 dB was used to map out the sound in the respective departments. Otoscopy was performed on the patients before commencement of Pure Tone Audiometry.

Pure-tone audiometry

The study was conducted in the quietest room possible (37 dB) within the central administration block after at least 14[10] h abstinence from noise, which allowed for recovery from temporary threshold shift. This might be less than optimal, but is still acceptable given a recent observation of the significant agreement between hearing threshold measured in nonsound-proof working environment and a sound-proof booth.[14] The procedure was explained to the participants; with a head phone using a manual diagnostic pure-tone audiometer (VMS Digi RSI Audiometer. Vaansari Marketing Services Chennai, Tamil Nadu, India), pure tone was sent into one of his ear, while the other one was masked (masking was done for bone conduction using a narrow band noise of 35 dB).[15] The procedure was similarly repeated in the other ear. An indicator was provided to the participant to press if he hears the sound while backing the examiner. Sound of different frequencies from 250 Hz to 8000 Hz was tested. The test started at 1 kHz then 2–8 kHz, and then 250 and 500 Hz. The stimulus was decreased by 10 dB every time the individual responds to the stimulus tone, and increase 5 dB if no response (Hughson–Westlake method). An automatic audiometric tracing was displayed on the screen and was printed out on an audiometric sheet. Both ears were alternately tested. The results were obtained immediately and interpreted.

Data management

The pure tone average was calculated at 500, 1000, 2000, and 4000 Hz and divided by 4 for each ear.[16] The presence of significant audiometric notch at 4 kHz was also considered, a 4 kHz notch was defined when the 4 kHz minus the 2 kHz threshold and the 4 kHz threshold minus the 8 kHz threshold were both >10 dB.[17] Hearing impairment was classified according to World Health Organization classification 2014.[18] Data obtained were calculated, entered, and analyzed using IBM SPSS (Statistical Package for Social Sciences) version 20 (IBM, Chicago, Illinois, USA).

  Results Top

A total of 318 individuals were recruited as the study group (23 were excluded because of ear pathologies from 341), with equal no. of controls. All participants were males in both groups. The study group had an age range of 20–56 (mean of 37.4 ± 8.85) years. The control group had an age range of 20–58 (mean of 37.5 ± 9.31) years [Table 1].
Table 1: Age distribution of participants in years

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Duration of employment of workers

[Figure 1] shows the distribution of duration of employment (years) in the factory, with 30.2%, 29.6%, 21.7%, 8.5%, and 10.1%, respectively, spending between 0 and 5, 6 and 10, 11 and 15, 16 and 20, and 21+ years in the factory/mill.
Figure 1: Duration of employment of workers in the noise-exposed sections of factory/mill

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Noise exposure duration per day

[Table 2] shows daily work duration in hours, with majority of workers (94.3%) worked for 0–8 h 5.7% worked for > 8 h daily.
Table 2: Duration of exposure in hours/day

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Symptomatology pattern (self-reported)

[Figure 2] shows the self-reported symptoms. In the study group, 6.3% of participants presented with complain of dizziness, 11.6% ringing sensation, and 10.1% hearing loss, whereas in the control group, 1.3% of participants presented with symptoms of dizziness, 2.2% ringing sensation, and none presented with perception of hearing loss.
Figure 2: Symptomatology

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Hearing threshold

[Table 3] shows a high prevalence of hearing loss in the factory,42.7% in both ears out of which 27.6% is symmetrical
Table 3: Prevalence of hearing loss in both ears

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Types of hearing loss

[Table 4] shows that according to the study, 31.8% of the participants with NIHL in the right ear (worse ear) had sensorineural, while 5.3% and 2.8% had conductive and mixed hearing loss, respectively, as against the control having 6.6%, 2.8%, and 0.0% being sensorineural, conductive, and mixed, respectively. In the left ear (better ear), 24.2% presented with sensori-neural, 4.1% conductive, and 3.5% mixed compared with 6.3%, 0.3%, and 0% having sensori-neural, conductive, and mixed hearing loss, respectively.
Table 4: Types of hearing loss

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Degree of hearing loss

[Table 5] highlights the degree of hearing loss in both the better and worse ears. About 22.3% of participants had mild, 8.7% moderate, and 1.3% severe hearing loss in the better ear.
Table 5: Degree of hearing loss

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Mean pure-tone averages in both ears

[Table 6] shows the mean Pure Tone Average at different frequencies for both ears, with 4Khz being worst affected in both ears [Table 6].
Table 6: Mean pure-tone averages in both ears at different frequencies in both ears' air conduction

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Classical notch at 4 kHz

[Table 7] shows classical notch at 4 kHz. About 14.5% have classical notch at 4 kHz in the left ear and 16.9% in the right ear.
Table 7: Classical notch at 4 KHz

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Correlation between mean pure-tone average and duration of employment

[Table 8] highlights the relationship between pure-tone average and length of duration of employment, which was found to be statistically significant.
Table 8: Pure-tone average and length of duration of employment

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Noise levels in various section of factories

[Table 9] shows noise levels at the various sections of the factory (76–104 dB-A, mean = 87.1 dB-A).
Table 9: Noise levels in various sections of the company/ participants exposed

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The highest noise level was recorded at the power house (103–105 dB-A, mean 104 dB-A), and the lowest noise level was recorded at the mobile clinic (74–78 dB-A, mean 76 dB-A).

  Discussion Top

A total of 318 individuals were recruited for the study (23 were excluded because of ear pathologies from 341) with equal number of controls. The age range for the noise-exposed participants was between 20 and 56 years (mean age of 37.4 ± 8.85), and the control group had an age range of 20–58 years (mean 37.5 ± 9.31). Majority of the participants fell within the fourth (43.7%) and fifth (24.8%) decades of life. The demographic pattern observed in this study is similar to what was obtained by other studies.[7],[17] The reason for this can be attributable to the preference of most industries to have vibrant and youthful workers to man the production sites, however no clear difference exists between young and older individuals in their susceptibility to NIHL,[2] but age may account for longer duration of employment and hence longer duration of noise exposure. The study population were all males and also the controls. In these part of the country, socio-cultural practice plays a greater role in deciding which kind of work women are expected to partake in, and women are hardly seen operating high-powered machines.[17] Hearing loss due to continuous or intermittent noise exposure increases rapidly during the first 10–15 years of exposure and the rate of hearing loss then decelerates as the hearing threshold increases.[19] In this study, it was observed that 40.2% of workers have worked for >10 years, while the majority worked for <10 years. This is similar to the observation made by Ali et al. in North East Nigeria, 30.2% worked for 0–5 years, 29.6% worked for 6–10 years, while 21.7%, 8.5%, and 10.1% worked for 11–15, 16–20, and 21+ years, respectively.[4] There was a statistically significant increase in pure-tone averages of participants (P = 0.000) when correlated with length of stay in the factory; workers with prolonged stay in the factory had their pure-tone average significantly increased.[7],[20] In this series, 94.3% of workers were working for 1–8 h per day, which is in tandem with international regulations.

The prevalence of NIHL in this study is similar to findings by other researchers; Ologe et al. reported prevalence of 28.2% among steel mill workers in Ilorin Nigeria,[7] and Kitcher et al. observed prevalence of 33.6% among stone crushers in Ghana.[21] However, it is lower than 67.1% reported by Ali et al. in a cement mill company in Gombe and 83% reported by Osibogun et al.[20] among textile workers in Lagos Nigeria. Such differences may reflect variation in factors including the sources and levels of noise exposure, duration of work in the industry, and other exposure to sociodemographic factors.[17] This study also demonstrated the presence of classical 4 kHz notch in the audiometric configuration of the patients compared to the controls. There was a prevalence of 14.5% and 17%, respectively, in the better and worst ear as against 2.8% and 3.1% in the controls, respectively; this is similar to the findings by other researchers.[22],[23],[24] However, Hong in a study to evaluate NIHL among construction workers in America did not find this sign.[25] The prevalence of hearing loss from the audiometric testing (42.7% in both ears) far exceeds the self-reported hearing loss (10.1%), which is not dissimilar to earlier studies.[17] Nondahl et al. confirmed a poor relationship between actual hearing losses in noise-exposed workers and suggested that the best practice requires inclusion of audiometric screening as part of a complete hearing loss prevention program.[26]

  Recommendations Top

Based on the findings in this research, the following recommendations were made:

  • Preemployment and periodic pure-tone audiometry screening while on the job to have a baseline hearing threshold of the worker and to detect early NIHL should be made mandatory
  • Training on the effect of noise pollution should hold periodically. This will serve as an avenue to discuss on the awareness of effect of noise pollution and emphasize on preventive measures and early warning signs of occupational NIHL
  • The use of hearing protection device should be made compulsory for every worker irrespective of his station within the noisy environment and also for visitors alike
  • Noise engineering control should be ensured such as replacement of old machines with newer and less noisy ones. Also, implementing the noise regulatory laws by relevant government agencies should be made mandatory
  • There is need for collaboration with otorhinolaryngologists for useful advice and appropriate intervention measures.

  Counseling Top

Counseling was done for both participants and management on occupational NIHL.

  Conclusion Top

This study has revealed a high prevalence of sensorineural hearing loss in the factory. This pattern of sensorineural hearing loss, coupled with the significant presence of 4 kHz audiometric notch among the noise-exposed workers (16.9%) in the worse ear when compared with the controls (3.1%) in the worse ear, strengthened the assertion that the hearing loss of the workers was likely attributable to occupational NIHL.

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Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Figure 1], [Figure 2]

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9]


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