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 Table of Contents  
Year : 2016  |  Volume : 22  |  Issue : 3  |  Page : 152-156

Hearing threshold of sawmillers in Kaduna, Nigeria

1 Department of ENT, Federal Medical Centre, Gusau, Zamfara, Nigeria
2 Department of Clinical Services, National Ear Care Centre, Kaduna, Nigeria
3 Department of Otorhinolaryngology, University of Ibadan, University College Hospital, Ibadan, Nigeria

Date of Web Publication8-Aug-2016

Correspondence Address:
Dr. Tijjani Sa’idu Abubakar
Department of ENT, Federal Medical Centre, Gusau, Zamfara
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0971-7749.187974

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Background: Hearing loss due to occupational noise exposure is a malady with millions of employees having occupational hearing loss (OHL) worldwide though under-appreciated. The neglect of hearing loss, especially OHL has resulted in human and economic consequences worldwide. The WHO estimates a global burden of 1.06 million in Sub-Saharan Africa. Nigeria is experiencing rapid industrial growth, and large number of workers are exposed to industrial noise. Prevention of noise-induced hearing loss is relatively simple and inexpensive. Aims and Objectives: This study was carried out to determine the pattern and prevalence of hearing loss among sawmillers at old Fanteka market, Kaduna. Materials and Methods: This was a cross-sectional descriptive study of the hearing threshold of sawmillers at the old Fanteka market, Kaduna. Ethical clearance was obtained from both the Kaduna state Ministry of Health and the National Ear Care Centre, Kaduna. Questionnaires were duly completed and thereafter the participants had pure tone audiometry in a soundproof booth. Noise meter was used to measure the sound level at the workplace and machines. Pure tone average was calculated for both the left and right ear. Statistical analysis was done using Statistical Package for Social Sciences (SPSS version 16.0, Chicago, Illinois, USA). Results: One hundred and twenty sawmillers with age- and sex-matched controls were assessed. Subjects' age ranged between 20 and 62 years, mean age of 31.36 ± 11.33, whereas controls' age ranged between 20 and 70 years, mean age of 33.29 ± 7.40. All the subjects were males. Prevalence of sensorineural hearing loss (SNHL) was 26.7%. Conclusion: Noise level within the study site environment ranged from 85 to 105 dB. The prevalence of SNHL was 26.70%, moderate type 9–16.70% by pure tone average bilaterally.

Keywords: Fanteka, Kaduna, Noise induced hearing loss, Occupational hazards, Saw millers

How to cite this article:
Abubakar TS, Labaran AS, Mohammed GM, Kirfi AM, Nwaorgu OG. Hearing threshold of sawmillers in Kaduna, Nigeria. Indian J Otol 2016;22:152-6

How to cite this URL:
Abubakar TS, Labaran AS, Mohammed GM, Kirfi AM, Nwaorgu OG. Hearing threshold of sawmillers in Kaduna, Nigeria. Indian J Otol [serial online] 2016 [cited 2021 Oct 23];22:152-6. Available from: https://www.indianjotol.org/text.asp?2016/22/3/152/187974

  Introduction Top

Hearing loss due to occupational noise exposure is a malady with millions of employees having occupational hearing loss (OHL) in the world. The neglect of hearing loss, especially OHL has resulted in human and economic consequences worldwide. The estimation of occupational diseases and disease-related condition was grossly underestimated in Sub-Saharan Africa or Africa in general. The WHO estimates a global burden of 1.06 million in Sub-Saharan Africa.[1] This is especially regrettable as noise-induced hearing loss (NIHL) is almost always preventable at relatively little cost.[2] Hearing impairment is the most frequent sensory deficit in human populations, affecting more than 250 million people in the world.[3],[4],[5],[6] Prevention of NIHL is relatively simple and inexpensive. Although the obvious and most desirable solution is to reduce noise from machinery and the environment to intensities below damaging levels; this is often impractical, expensive, or scientifically impossible.

Man's discovery of the use of metals, first bronze later iron with the attendant noises of beating, hammering, and forging to fashion useful implements and weapons, was perhaps the first situation in which human hearing was at risk from occupational noise.[7],[8],[9],[10],[11],[12] The amount of hazards a worker can reasonably be exposed to is not defined by statute and was left to the benevolence of industrial employers as was the case during the industrial revolution in Europe.[13],[14],[15],[16],[17],[18] Noise-induced permanent threshold shift is considered one of the most frequent occupational health hazards in both industrial and military environment.[19] Nigeria is experiencing rapid industrial growth and a large number of workers are exposed to industrial noise, but only a few studies have been done to assess the effect of noise on hearing of the workers. Thus, this study is aimed at determining the hearing threshold of sawmillers at the old Fanteka market, Kaduna, and prevalence of hearing loss among them. It is hoped it will also help increase the knowledge on the effect of noise on hearing of sawmillers in Nigeria, and that recommendations arising from it will catch the attention of the authorities concerned.

  Materials and Methods Top

This was a cross-sectional descriptive study of all sawmillers at the old Fanteka market, Kaduna exposed to the machines that may result to hearing loss. The audiometric assessment was undertaken in the Audiology Department of the National Ear Care Centre in a soundproof booth. Ethical clearance was obtained from both the Kaduna state Ministry of Health and the National Ear Care Centre, Kaduna. All sawmillers at the old Fanteka market aged 20 years and above who have worked for over 1-year as sawmillers in the Fanteka market to ensure significant exposure time to the noise of the machines and consented to participate voluntarily participated in the study. A control group matched for gender and age, and not exposed to sawmill machines was selected from the public traders at the same Fanteka market site. They were assigned study numbers. Questionnaire which gave information on demographic variables - age, sex, occupation, and duration of exposure was administered.

A thorough ear examination was conducted before and after the study. Pure tone audiometry was done using MAICO MA42 audiometer made in Japan, whereas the ambient noise level was measured using TES1350A sound level meter made in Taiwan while tympanometry was done to ensure inclusion of participants with only normal value.

Pure tone average of the left and right ears was calculated. This is the average hearing threshold level for the pure tone frequencies of 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz. Pure tone average for each ear was used to determine the level of hearing for that ear. Hearing loss was classified using the commonly used grading system.[19]

The collected data were coded and entered into computer, analyzed with Statistical Package for Social Sciences (SPSS version 16.0, SPSS Inc., Chicago, Illinois, USA). Demographic variables were presented in the form of tables and charts, means, and proportions were summarized. Chi-square was used for the test of association for categorical variables, whereas for quantitative variable test of association was done using t-test. Level of statistical significance was set at P < 0.05.

  Results Top

A total of 120 sawmillers were assessed in this study, matched with a control of 100 participants from separate areas of the same market.

The noise level range at the machines site workstation was 100–105 dB. Ambient noise range within the market was 80–85 dB.

Age range of participants/subjects was between 20–73 years and 20–76 years in the study and control groups, respectively [Table 1].
Table 1: Age distribution of the participants

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Majority of the participants are within the 30–39 age group.

Educational level was evaluated, and participants were grouped into those having formal education and those without formal education. Sixty-three participants (52.5%) had formal education, whereas 47.5% had no formal education.

Duration of work

Seventy-six (63.30%) and 44 (36.70%) of the participants had been on the job for 1–10 years and 11 years and above in the sawmill, respectively.

Models of machines

More than 80% of the participants were using the old model machine, whereas 20% did not respond to the type of machines they are using. All the machines inspected were older than 20 years in use.

Majority of the workers (59.20%) in this study were cutting and planning the wood, whereas transporters and those trading it constituted 16.70% and 24.20%, respectively.

On duration of exposure, majority of the study group (72.50%) worked for 1–8 h/day, whereas 27.5% worked for more than 8 h a day.

On the knowledge of if the work in the sawmill affected hearing or not, 69 (57.5%) respondents were positive, whereas 42.5% said there was no effect noted.

Use of hearing protective device

More than 90% agreed that use of hearing protective device is important with only 9 (7.5%) of the study group doing so with cell phone earpiece and not earmuff or any form of protective devices. Cell phone earpiece is not an approved hearing protective device; however, they use it erroneously thinking that it protects them from having hearing loss.

[Table 2]a showed that 34 respondents had hearing loss in the left ear compared with 30 in the right, P = 0.470, a finding which is not significant. Thus, 64 (26.67%) ears had sensorineural hearing loss (SNHL).
Table 2

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A total of 24 (12%) ears out of 200 for the control had SNHL equally distributed (12 each) between the left and right ears [Table 2]b.

Test of association (Chi-square test) in [Table 2]c shows that P = 0.001; inferring that hearing loss is significantly more in sawmillers than control.

Thirty ears (12.5%) of the study group's pure tone audiogram showed the classical notch at 4 kHz.

Test of association in [Table 3]a shows a P = 0.001 with degree of freedom of 1; a finding which is significant indicating that the higher the years of exposure the more the chance of developing hearing loss [Table 3]b.
Table 3

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  Discussion Top

Woodworkers in sawmills are exposed to the development of NIHL as an occupational hazard.[13],[20] The risk of developing the hearing loss increases over time for those exposed to industrial noise more than 85 dB.[21],[22] In this series, the noise level at the machines site was 100–105 dB, which is far higher than the recommended noise level of 85–90 dB in industrial sites.[23],[24],[25]

The age range of the study population was 20–73 years of which most of the studies have similar age groups.[26]

In this present study, 72.50% of the study population was working for 1–8 h/day which agrees with the international regulation.[27],[28]

In this study, 26.67% and 12% of the study and control groups, respectively, had SNHL. This was found to be statistically significant with P = 0.001. This shows that the exposure to noise plays a significant role in the development of the hearing loss among sawmillers.

The prevalence of hearing loss in this study is higher than those found in other parts of the world. In India, the prevalence of noise-induced SNHL was in the range of 7–12%, even though it is a developing country like Nigeria.[20]

This high prevalence may be related to the type of machines used as the study showed that all the machines in use are old model type. Furthermore, poor hearing protective practice may be contributory as the study showed that even though 57.5% of the workers admitted that working in the sawmill can affect hearing, only 7.5% actually used inappropriate “hearing protective device” in the form of the earpiece of cell phones only and not any other form of protective devices.[29],[30],[31],[32]

The discordance in the use of hearing protective device versus knowledge was also recorded by Tanimola and Julius [32] and Ologe et al.,[33],[34] these showed that up to 78.2% of workers in the noisy industries admit knowledge that blocking their ears reduces the chances of developing hearing loss.

In the USA [35] now, the prevalence of noise-induced SNHL is <10%, probably due to the use of recent modern machines with low noise threshold, use of protective devices due to the awareness, and their level of education. In Ghana,[36] it was found to be 20%.

Tympanometry was done to all the study group and the control, and all those who had any reading apart from Type A were dropped and replaced with those having normal reading. This was done to exclude the contribution of any middle ear pathology to the observed hearing thresholds.

In this series, about 12.5% ears have the classical notch at the 4 kHz frequency. Among the 13 subjects (12.5%) who had a classical notch at 4 kHz frequency, eight (7.69%) had bilateral, five (4.81%) unilateral with three (2.89%) left, and two (1.92%) right ear, respectively. This is less than half of the values in other studies.[27] Krishnamurti [35] found 27% in this series, a feature further confirmed by Rabinowitz et al.[37] Statistically significant relationship was demonstrated between the development of hearing loss and duration of exposure to the sawmill both in terms of hours of work per day and total length of work in years. This trend is the expected as it has been seen in other studies within and outside the country, Nelson et al.,[6] Oleru et al.,[11] Ahmed et al.,[24] Boateng and Amedofu,[36] Akande and Ologe,[38] among others.

From the findings of this study, it is desirable to encourage routine and yearly periodic audiological examination to screen as well as advise these group on the risk inherent in their job, while enlightening them on the benefits of use of newer machines with very low intensity of sound or with silencers so as to reduce the noise at the working environment. There is also the need to ensure compliance with observation on noise control at the market sawmill and encourage the procurement and use of appropriate hearing protective devices.

  Conclusion Top

In this study, it was found that the prevalence of NIHL is high compared with findings from other regions and as such the need for creation of more awareness so as to reduce its prevalence.

The study also showed that those with moderate SNHL are more in the study group compared with the control with the classical notch at the 4 kHz frequency seen only in the study group.

It also noted that the knowledge and use of hearing protective devices are very poor; this may have contributed to the increased prevalence in the study group.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Table 1], [Table 2], [Table 3]


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