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ORIGINAL ARTICLE
Year : 2018  |  Volume : 22  |  Issue : 1  |  Page : 11-16
 

Hearing threshold status and risk estimate of hearing impairment among administrative workforce


1 Division of Physiology and Ergonomics, ICMR—National Institute of Occupational Health, Ahmedabad, Gujarat, India
2 Occupational Psychology, ICMR—National Institute of Occupational Health, Ahmedabad, Gujarat, India
3 Nirma University, Ahmedabad, Gujarat, India

Date of Web Publication18-Apr-2018

Correspondence Address:
Mr. Joydeep Majumder
Division of Physiology and Ergonomics, ICMR—National Institute of Occupational Health, Ahmedabad - 380 016, Gujarat
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijoem.IJOEM_22_18

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  Abstract 


Background: Administrative workers working in quieter environment workplace are considered unaffected by noise-induced hearing loss (NIHL). Aim: To create a baseline data of the administrative workers so as to monitor them with prospective years of exposure with the hypothesis that workers working in the administrative jobs may not be affected by NIHL. Settings and Design: The study was conducted among men and women administrative workers working in an office in Ahmedabad city, India. The design of the study was prospective cross-sectional study. Materials and Methods: In all, 64 men and 33 women administrative workers were recruited. Pure tone air conduction (AC) and unmasked bone conduction (BC) audiometry of both ears was performed. Pure tone averages (PTAs) and air-bone gap (ABG) were calculated. Excess risk of hearing impairment was estimated using five model equations. Statistical Analysis: Descriptive statistics was used for analysis. For calculation of excess risk of hearing impairment, models in online calculator were used. Results: AC for men depicted 4 and 6 kHz notch, whereas 6 kHz for women, for both ears. Around three-fourth men and nine-tenth women recorded hearing threshold <25 dB (A) for PTA0.5-1-2-4. ABG was <15 dB at all frequencies except 6 kHz, for both groups. Highest values of average estimated excess risk were 4.89% and 1.21% for men and women, respectively. Estimated excess risk ranged up to 1% for 50%–77% men and 82%–91% women. Conclusion: Administrative workers are minimally risked of developing NIHL; however, with progressive age, hearing ability may deteriorate.


Keywords: Administrative workers, air-bone gap, air conduction, audiometry, bone conduction, excess risk estimate, gender difference, hearing loss, noise-induced hearing loss, pure tone averages


How to cite this article:
Majumder J, Patel RC, Kotadiya S, Shah P. Hearing threshold status and risk estimate of hearing impairment among administrative workforce. Indian J Occup Environ Med 2018;22:11-6

How to cite this URL:
Majumder J, Patel RC, Kotadiya S, Shah P. Hearing threshold status and risk estimate of hearing impairment among administrative workforce. Indian J Occup Environ Med [serial online] 2018 [cited 2019 Aug 25];22:11-6. Available from: http://www.ijoem.com/text.asp?2018/22/1/11/230349





  Introduction Top


Noise is one of the most pervasive problems in today's occupational environment, affecting workers in manufacturing, construction, transportation, agriculture, military, and so on. Especially workers working in noisy environment such as shop floors, production, and maintenance are ought to be affected by noise. Administrative workers are considered to be working in quieter environment having minimal hearing effects. All over the globe, comparative research studies on occupational noise have considered administrative workers as controls.[1],[2] In India, study conducted on shipyard employees was compared with office workers as controls. Among the exposed workers, 6% were assessed to have a noise-induced hearing loss (NIHL), when compared with none among office workers.[3] Various epidemiologic studies iterated annoyance as considerable at an equivalent sound levels >55 dB.[4],[5] In offices, conversational speech and appliances such as air conditioners and cooling fan in CPU of the computer also create annoyance, even if the intensity may be less than 55 dB. Although significant evidence exists that exposure to sound below an intensity of 77–80 dB will not cause any hearing loss, tinnitus, or any other noise-related diseases. Although office environment is considered to be quiet, it may not be relevant to exclude the vulnerability of hearing impairment among office workers. Research among office workers revealed hearing threshold below 29 dB in all frequencies compared with workers in other noise-induced occupations.[6],[7] Research concentrating on office workers, their working environment, duration of exposure, and related history would determine their audiometric profile and any need of intervention. Environmental noise at workplace, community noise, personal habits, and so on can also affect hearing quality among individuals.

Ample literature reports the association of age and deteriorating hearing thresholds, although NIOSH (1998) reported that not all people experience decrease in hearing sensitivity with age.[8] It would also be important to research into the effect of noise on the hearing profile of the workers based on gender classification. Literature reports difference in hearing loss and gender.[9],[10] Whether men or women, literature reports that only audiogram-based diagnosis with notch at a particular frequency is not enough to rule out NIHL.[11] Despite this, there remains disagreement wherein some researchers considered a notch as proof of NIHL.[12],[13] The notch at 4 kHz may be a clinical sign of NIHL and may be valuable in confirming the diagnosis; however, the 6-kHz notch is variable and may be cautiously interpreted for NIHL diagnosis. Phillips et al. reported the 4–6 kHz bilateral notch as a feasible phenotype for identifying genetic susceptibility to hearing loss.[14] In addition to audiometric notch confirming the diagnosis of NIHL, observed history of excessive occupational or non-occupational noise exposure was reported as an important factor in the confirmation of NIHL.[15] This calls for strict monitoring of the workplace noise level, periodic audiometric checkup, shape of the audiogram, and detailed history of the workers in particular.

There has been an increasing trend of assessing the hearing profile change in noise-exposed population and following them longitudinally. Although hearing profile based on aging is additive to NIHL, age-adjusted assessment of hearing loss is not adequately reported. Therefore, this study attempted to create a baseline data of administrative workers so as to monitor them with prospective years of exposure with the hypothesis that workers working in administrative jobs may not be affected by NIHL.


  Materials and Methods Top


Participants

The study was conducted among 64 men and 33 women administrative workers working in an office in Ahmedabad city, India. The selected workers were exposed to equivalent noise levels (LAeq (8 h)) of 60–65 dB(A) at their workplace. The study was approved by the Human Ethics Committee of the Institute. A detailed written informed consent to participate in the study was taken from all the participants.

The blood pressure and heart rate were measured after 10 min of rest from the arrival of the volunteer in the laboratory. An international classification to categorize hypertension of people referred to as JNC 7 criterion was followed.

The demographic profile of the volunteers was recorded which included age, education, designation, approximate time spent in office, and details of their present and past occupational history.

The audiometric tests were then conducted in an audiometric chamber. The designed chamber had an outside to inside Sound Transmission Class (STC) of >40 dB at 1 kHz. Before audiometric measurement, the volunteers were explained about the study and testing protocol. They were allowed a test session to get an understanding of the test, noise exposure, and their response. Before the experiment, it was ensured that the test environment was quiet and free of distractions to the test volunteer and the experimenter.

Pure tone audiometry

The testing was performed using GSI 61 Clinical Audiometer (Grason-Stadler Inc., Littleton, MA, USA). Pure tone audiometry was performed on both ears, one at a time, at frequencies of 0.125, 0.250, 0.5, 0.750, 1, 1.5, 2, 3, 4, 6, and 8 kHz. Before the test, the volunteer was enquired to identify his or her better ear. On confirmation, the test was started for his or her better ear. In case, he or she could not notice any difference between the right and left ears, the test was started in the right ear at 1000 Hz (intensity, 30 dB hearing level) proceeding to higher octave frequencies. After testing at 8000 Hz, lower octave frequencies were evaluated starting at 125–750 Hz. In case of a no response at 30 dB, the intensity was increased in 10 dB steps until a response was recorded and then the descending bracketing method was initiated again. A pulsed tone of more than 200 ms duration was given for each frequency being tested. Volunteers were instructed to press a hand-held response switch upon hearing a tone, to hold the key down as long as they hear the tone, and to release it when they no longer hear the tone. A short rest period was given in between testing of right and left ears for air conduction (AC) and bone conduction (BC) audiometry.

Bone conduction audiometry

BC was done for both the ears (one each at a time) at frequencies of 0.250, 0.05, 1, 1.5, 2, 3, 4, 6, and 8 kHz placing the vibrator on the mastoid bone. The threshold-seeking paradigm used the same threshold-seeking method used in the pure tone test configuration. All tests were completed on the same day for all subjects.

The threshold levels at all measured frequencies for AC and BC audiometry were plotted as an audiogram to graphically show the hearing loss trends.

Pure tone averages

From the audiogram, hearing impairment for conversational speech was calculated as the pure tone average (PTA) for the better ear as an average of four frequencies (0.5, 1, 2, and 4 kHz).[16] These frequencies are typical for normal conversational speech. The World Health Organization (WHO) classified hearing loss according to the PTA in the better hearing ear as normal hearing <25 dB hearing threshold level (HL), mild hearing loss = 26–40 dB HL, moderate hearing impairment = 41–60 dB HL, and severe hearing impairment = 61–80 dB HL.

Excess risk of hearing impairment

The estimated excess risk of hearing impairment was calculated from the measured audiometric data using five most commonly used model equations. These equations are taken from the American Academy of Otolaryngology,[17] American Academy of Ophthalmology and Otolaryngology,[18] National Institute of Occupational Safety and Health,[8] and British Society of Audiology.[19] The equations determined average hearing loss for a range of frequencies (0.5–4.0 kHz). These equations used low and high fences of 25 and 92 dB(A), representing 0% and 100% hearing handicap boundaries, respectively. The low fence of 25 dB(A) represents normal hearing. The calculator developed by Kavanagh was used to calculate estimated excess risk of hearing impairment of administrative workers using selected model equations.[20]


  Results Top


The demographic details of workers are reported in [Table 1]. All administrative workers reported working for ~8 h daily for 5 days a week. Around 15%–24% of the studied workers reported noisy environment around their dwellings due to nearby traffic. In addition, it was noted that only ~7% of them had the habit of using earphones either for music or attending to phone calls for an average time of ~1 h/day. As per JNC 7 criteria, 52.6% of all volunteers recorded normal blood pressure (BP), 35.8% as pre-hypertensive, 10.5% as hypertensive stage 1, and 1% as hypertensive stage 2.
Table 1: General characteristics of participants

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[Figure 1] shows the audiogram of men and women for AC and BC audiometry for both ears. AC hearing thresholds for men depicted that the threshold values for both ears were within 25 dB for 0.25–2 kHz. A dip/notch was observed at frequencies of 4 and 6 kHz. For women however, the threshold values were within 25 dB at all frequencies tested. However, a notch was seen in the 6-kHz frequency. The average threshold at 6 kHz was recorded as 23 dB for both right and left ears. Unmasked BC threshold audiometry revealed that for both men and women, the threshold values were lower than that of the AC values except in 2 kHz for men and 2 and 3 kHz for women, where the values nearly coincide with AC values. Furthermore, it was also noted that the pattern of air-bone gap (ABG) among men and women was identical. The ABG was observed to be less than 15 dB for all frequencies except for 6 kHz in both ears among men and women [Figure 2].
Figure 1: Audiogram of the men and women for air conduction and bone conduction audiometry for both ears. RAC: Air conduction (right ear), LAC: Air conduction (left ear), RBC: Bone conduction (right ear), LBC: Bone conduction (left ear)

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Figure 2: Air-bone gap for right and left ear among men and women. RT: Right ear, LT: Left ear

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The average PTA0.5-1-2-4 for men on right and left ears was 23.2 and 23.6 dB, respectively. For women, PTA0.5-1-2-4 on right and left ears was 23.3 and 23.5 dB, respectively. Analysis revealed that more than half of both men and women recorded right ear as the better ear with average PTA0.5-1-2-4 noted as 21.2 dB for both men and women. The hearing impairment classification as per better ear PTA0.5-1-2-4 for both men and women is presented in [Table 2]. It is observed that approx. three-fourths of men and nine-tenth of women had hearing threshold below 25 dB for PTA0.5-1-2-4, so as to be considered to have normal hearing status. Volunteers who were calculated to have hearing threshold above 25 dB were in the age range of 43–64 years (men: 52.9 ± 7.1 years; women: 52.8 ± 6.0 years).
Table 2: Pure tone average for the better ear (PTA0.5-1-2-4) in the study population

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[Table 3] shows the highest values of average estimated excess risk of hearing impairment, which were 4.89% and 1.21% for men and women, respectively, with different model equations. The average estimated excess risk of hearing impairment was the highest with NIOSH, 1998 model for men and British Society of Audiology model for women. The finding also shows that the mean audiometric threshold values for both ears were the highest at 6 kHz frequency for men and 0.5 kHz frequency for women. The estimated excess risk of hearing impairment with different models ranged up to 1% for 50%–77% of men and 82%–91% of women.
Table 3: Excess risk of hearing impairment in the study population

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The audiometric analysis also suggested that the effect of noise levels and duration of exposure was dependent on frequency.


  Discussion Top


With the hypothesis that workers working in administrative jobs may not be affected by NIHL, office workers are considered as controls in almost all research studies on noise and health. Persistent with the existing literature, the result of this study indicated that office workers working in quiet office environment do not have hearing impairment to the extent of NIHL. However, with prevailing noise, even in a quiet office environment, the auditory and non-auditory effects on such exposed population could not be ruled out. This study was therefore an attempt to create a baseline data of office workers, so that they can be monitored with prospective years of exposure.

As revealed from demographic details of workers, the recruited volunteers worked in a standard 8-h schedule for 5 days a week. Around one-fourth of them were exposed to some noise around their habitats. In addition, the habit of using earphones either for music or attending to phone was meager. This implies that exposure to noise was restricted among the population studied.

As seen in the audiogram, AC hearing thresholds for men depicted dip/notch at 4 and 6 kHz. The findings were consistent with an earlier study reported on office workers at Kolkata, India.[21] Nondahl et al. state that presence/absence of a notch may be an unreliable indicator of NIHL.[11] Thus, the notch seen in high-frequency audiogram (6 kHz) does not exclude the possibility of NIHL. Literature also reveals that besides the shape of audiogram, detailed occupational history plays a predominant role to understand the NIHL. Considering the average age of the sample, hearing threshold at 8 kHz is seen to have revived after the notch at 6 kHz (except for left ear in men), predicting less chances of presbycusis, although NIOSH states that not all people experience decrease in hearing sensitivity with age.[8]

BC hearing thresholds are affected by an outer or middle ear lesion, although the alteration is small compared with the change in AC thresholds. In this study, the results of unmasked BC audiometry were similar to the study reported by Swanepoel and Biagio wherein the AC and BC values coincided at 2 kHz.[22] As observed that the ABG was less than 15 dB for all frequencies except for 6 kHz in both ears among men and women [Figure 2], it is an important link toward focusing for hearing conservation. For hearing conservation, hearing protectors such as ear muffs and plugs are commonly used; however, the transmission of sound is 50–60 dB below the BC–AC sensitivity at frequencies below 1 kHz. At higher frequencies, the BC–AC sensitivity is a minimum of 40–50 dB at 2 and 8 kHz and a maximum of 50–60 dB at 4 kHz.[23] Hence, at condition of higher BC audiometric values, the BC sound transmission needs attenuation, e.g. helmets could be used.[24]

As per WHO, a speech-frequency pure-tone average (PTA0.5-1-2-4) of greater than 25 dB hearing loss is the initiation of communication impairment in daily life.[16] Various researchers used PTA for three to four frequencies in the conversational frequency scale; however, PTA0.5-1-2-4 has been widely used.[25],[26] In a comparative study among noise-exposed workers and administrative workers, it was reported that only 5% of administrative workers were having PTA above 25 dB(A).[27] In this study, the number of administrative workers having PTA above 25 dB(A) is slightly more. Perhaps, PTA has a much bigger role in understanding the gravity of hearing loss in terms of exposure to noise. A study by Gianoli and Li reports that among patients with sensorineural hearing loss, 44% of them were documented with improvement in PTA on administration of transtympanic steroid therapy.[28] This study iterated that hearing loss due to noise exposure or otherwise may result in permanent threshold shift and would be irreparable, thereby calling for noise monitoring at workplace, periodic audiometric surveillance, and hearing protection devices.

The audiometric analysis suggested that hearing damage at 3, 4, and 6 kHz was expected to occur sooner than hearing loss at lower conversational speech frequencies (0.5, 1, or 2 kHz). Certainly, the effect of noise levels and duration of exposure was dependent on frequency. As depicted in [Table 3], the highest values of average estimated excess risk of hearing impairment are 4.89% and 1.21% for men and women, respectively, with different model equations. As per audiogram in this study, the threshold values were observed to be elevated, for the frequencies used in the models. This depicted higher estimated excess risk among men when compared to earlier reported comparative study on drivers and office workers.[21] It may be noted that average estimated excess risk of hearing impairment using models that exclude higher frequencies is less sensitive to noise damage and may require longer duration of exposure to a given sound level to experience significant excess risk in the population.

The advantage of our study was its prospective design and the fact that the sample was representative of the working population from both genders in quiet office environment. Furthermore, the occupational history was complete for all volunteers studied, and a substantial selection bias is unlikely. In addition, nine-tenth of the studied volunteers were below the age of 50 years, which gives us a fair chance to longitudinally follow them up for prospective years of noise exposure at their workplace in relation to NIHL. However, the authors feel that there were some substantive limitations to the study. Although the occupation data were obtained from highly valid registry, there could be recall bias in the self-reported health problems by the volunteers. Second, the role of age as a potential confounder was not considered because of moderate sample size. The results of this study may be carefully interpreted because the study sample size is moderate, and risk estimate of hearing handicap may not have been found to be statistically significant due to inadequate statistical power.

The potential effect of noise exposure to workers may be reduced by hearing protection devices; however, self-reported by workers that devices contribute to interference in speech communications. Although office workers are at minimal risk of developing NIHL, hearing ability may deteriorate with progressive age. Therefore, for workers working in offices, periodic audiometric checkup would determine their auditory threshold profile and understand the progressive loss and the need of any engineering or personal intervention. With the limitation of a moderate sample size, the findings are a trend of the audiometric profile of the workers in administrative jobs. In the presented data, office workers are seen with higher hearing thresholds at higher frequencies which might be a warning sign with years of exposure to workplace noise.

Acknowledgements

The authors thank the Director, ICMR—National Institute of Occupational Health, Ahmedabad, for permitting to conduct this study. The authors are indebted to Mrs. Bina G. Shah and Mr. D.S. Kshirsagar for recruitment of participants and assistance during the study.

This article was presented at the 14th International Conference on Humanizing Work and Work Environment from December 8 to 11, 2016, at Dr BR Ambedkar National Institute of Technology, Jalandhar 144011, Punjab, India.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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