Occupational Exposure to Noise and Age-related Hearing Loss in an Elderly Population of Southern Italy
Luigi De Maria1, Antonio Caputi1, Rodolfo Sardone2, Enza Sabrina Silvana Cannone1, Francesca Mansi1, Francesco Birtolo1, Maria Celeste Delfino1, Domenica Cavone1, Luigi Vimercati1, *
1 Interdisciplinary Department of Medicine, University of Bari, Bari, Italy.
2 National Institute of Gastroenterology-Research Hospital, IRCCS 'Saverio de Bellis', Castellana Grotte, Bari, Italy.
Age-Related Hearing Loss (ARHL) is a gradual and irreversible age-dependent decline in auditory function. There is still no consensus on the long-term functional effects of noise exposure on ARHL.
This study aimed to compare the prevalence of ARHL in an elderly population occupationally exposed to noise in a non-exposed population.
The population was divided into two groups: a group of 482 subjects professionally exposed to noise for over 10 years and a group of 1129 non-exposed subjects. Among the exposed subjects, a subgroup of 298 who worked for over 10 years in the glassware industry was selected. All the participants underwent a thorough otorhinolaryngological examination.
The presence of ARHL was found in 81% of exposed subjects and in 4% of non-exposed subjects. In the sub-group of glassware workers, the prevalence was 88%. The statistical analysis showed a significant association between previous occupational exposure to noise and ARHL (OR = 1.09; 95% CI = 1.067-1.124; p = 0.0012) and between exposure to the glassware industry and ARHL (OR = 1.89; 95% CI = 1.78-1.96; p = 0.006).
Consistent with recent studies, we found a significantly higher prevalence of ARHL among workers exposed to noise; however, further studies are needed to support these findings.
open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: https://creativecommons.org/licenses/by/4.0/legalcode. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
* Address correspondence to this author at Interdisciplinary Department of Medicine, University of Bari, Bari, Italy. Tel: 0039-080-5478256,
Occupational Exposure to Noise and Age-related Hearing Loss in an Elderly Population of Southern Italy
The environmental and occupational health risk factors due to exposure to chemical, carcinogenic, physical and biological agents are heterogeneous [1Afrifa J, Opoku YK, Gyamerah EO, Ashiagbor G, Sorkpor RD. The clinical importance of the mercury problem in artisanal small-scale gold mining. Front Public Health 2019 May 29; 7(131) Ecollection. Review [http://dx.doi.org/10.3389/fpubh.2019.00131] -20Vimercati L, Fucilli F, Cavone D, et al. Radon levels in indoor environments of the university hospital in bari-apulia region southern italy. Int J Environ Res Public Health 2018; 15(4): 694. [http://dx.doi.org/10.3390/ijerph15040694] [PMID: 29642436] ].
Noise is a physical agent that causes noise-induced hearing loss (NIHL). NIHL has long been recognized as an occupation- al disease. It is the consequence of overexposure to loud noise, characterized by a permanent increase in auditory thresholds [21Clark WW, Bohne BA. Effects of noise on hearing. JAMA 1999; 281(17): 1658-9. [http://dx.doi.org/10.1001/jama.281.17.1658] [PMID: 10235164] -25Basner M, Babisch W, Davis A, et al. Auditory and non-auditory effects of noise on health. Lancet 2014; 383(9925): 1325-32. [http://dx.doi.org/10.1016/S0140-6736(13)61613-X] [PMID: 24183105] ]. It has been suggested that 12% or more of the global population is at risk of hearing loss from noise, which equates to well over 600 million people [26Alberti PW, Symons F, Hyde ML. Occupational hearing loss. The significance of asymmetrical hearing thresholds. Acta Otolaryngol 1979; 87(3-4): 255-63. [http://dx.doi.org/10.3109/00016487909126417] [PMID: 443006] ]. The World Health Organization estimated that one-third of all cases of hearing loss can be attributed to noise exposure [27Noise and Hearing Loss National Institutes of Health Consensus Development Conference Statement 1990. Edited by: Services USDoHH. Bethesda, MB: Available from: https://consensus.nih.gov/ 1990/1990noisehearingloss076html.htm].
Age-related hearing loss (ARHL), or presbycusis in the human clinic, is a gradual and irreversible age-dependent decline in auditory function, which is reflected in a progressive increase in auditory thresholds, mainly in the high-frequency range [28Gates GA, Mills JH. Presbycusis. Lancet 2005; 366(9491): 1111-20. [http://dx.doi.org/10.1016/S0140-6736(05)67423-5] [PMID: 16182900] ].
Subjects present degraded frequency discrimination and limitations in speech comprehension tasks [29Boettcher FA. Presbyacusis and the auditory brainstem response. J Speech Lang Hear Res 2002; 45(6): 1249-61. [http://dx.doi.org/10.1044/1092-4388(2002/100)] [PMID: 12546491] -34Sprinzl GM, Riechelmann H. Current trends in treating hearing loss in elderly people: a review of the technology and treatment options - a mini-review. Gerontology 2010; 56(3): 351-8. [http://dx.doi.org/10.1159/000275062] [PMID: 20090297] ]. ARHL is a well-recognized condition in older age, with a high prevalence in the general population of approximately 20% in individuals over 65 years old but increasing to 65% in individuals over 85 years old [35Lin FR, Thorpe R, Gordon-Salant S, Ferrucci L. Hearing loss prevalence and risk factors among older adults in the United States. J Gerontol A Biol Sci Med Sci 2011; 66(5): 582-90. [http://dx.doi.org/10.1093/gerona/glr002] [PMID: 21357188] ]. Both age-related hearing loss (ARHL) and noise-induced hearing loss (NIHL) may share pathophysiological mechanisms in that they are associated with excessive free radical formation and cochlear blood flow reduction, leading to cochlear damage [36Mills DM, Schmiedt RA. Metabolic presbycusis: differential changes in auditory brainstem and otoacoustic emission responses with chronic furosemide application in the gerbil. J Assoc Res Otolaryngol 2004; 5(1): 1-10. [http://dx.doi.org/10.1007/s10162-003-4004-3] [PMID: 14605922] ]. They can be distinguished only on the basis of the period in which they occur and the specific risk factors with which they are associated. NIHL and ARHL are often presented simultaneously and represent a continuum in which the former becomes a powerful causal risk factor for the latter. Therefore, it is possible that occupational noise exposure may add to cochlear ageing mechanisms, having an impact on the onset and/or progression of ARHL. Nevertheless, although there is substantial information on noise and ageing, there is still no consensus on the long-term functional effects of noise exposure on ARHL [37Fetoni AR, Picciotti PM, Paludetti G, Troiani D. Pathogenesis of presbycusis in animal models: a review. Exp Gerontol 2011; 46(6): 413-25. [http://dx.doi.org/10.1016/j.exger.2010.12.003] [PMID: 21211561] ].
Therefore, the aim of the present study was to evaluate the prevalence of ARHL in an elderly population occupationally exposed to noise compared with a non-exposed population residing in Castellana Grotte, a small town in the Apulia region of southern Italy, and the surrounding area.
2. MATERIALS AND METHODS
Between January 2013 and August 2017, a sample of 1611 subjects (769 males, 842 females; average age 73.8 years, SD ± 6), living independently or institutionalized, was randomly selected from the electoral rolls of eight Italian municipalities after stratification for age and gender. All subjects are part of “The Great-AGE Study”, an on-going population-based study on ageing conducted in Castellana Grotte, a small town in the Apulia region, southern Italy [38Sardone R, Battista P, Tortelli R, Piccininni M, Coppola F, Guerra V. Relationship between central and peripheral presbycusis and mild cognitive impairment in a population-based study of Southern Italy: the “Great Age Study Neurology Apr 2018; 90(15 Suppl): 1.131.https://n.neurology.org/content/90/15_Supplement/P1.131]. The study population was divided into a group of subjects exposed professionally to noise for a period of less than 10 years or not at all (n = 1129) and a
group of subjects professionally exposed to noise for over 10 years (n = 482). Among these, a subgroup of 298 subjects who worked for over 10 years in the glassware industry in Castellana Grotte and who were professionally exposed to noise levels were selected, as shown by environmental monitoring findings in Table 1.
Voluntary informed consent was obtained from the subjects and/or their relatives before enrolment. All subjects underwent an otorhinolaryngological examination at the National Institute of Gastroenterology-Research Hospital IRCCS 'Saverio de Bellis' in Castellana Grotte, which consisted of recording medical history to reconstruct the following: occupational exposure to noise and ototoxic substances; the presence of tinnitus; otoscopy with occluding cerumen removal; tympanometry; and stapedial reflex to discriminate hearing loss from other inner-ear pathologies. Finally, an assessment of auditory function was performed using tonal audiometry and language.
Pure tone audiometry was performed in a standardized manner, and the identification of synthetic sentences with ipsilateral competing message (SSI-ICM), adapted and validated in the Italian language, was performed in a soundproofed room.
Air conduction thresholds for both ears were registered and stored in a database. The following frequencies were tested: 0.5 kHz, 1 kHz, and 2 kHz. The ascending method was used, and ISO 389 and ISO 8253-1 standards were applied. The tests were performed in quiet office rooms in the same building. Hearing loss is established on the basis of the classification of four stages of deficit in the best ear, identified through the BIAP scale [39International Bureau for Audiophonology. BIAP Recommendation 02/1 Audiometric Classification of Hearing Impairments 1997.https://www.biap.org/en/recommandations/recommendations/tc-02-classification/213-rec-02-1-en-audiometric-classification-of-hearing-impairments/file]. Trained clinical audiologists performed the tests (air and bone conduction thresholds). Masking was performed when applicable.
The purpose of environmental monitoring in the glassware industry was to assess the exposure to noise of workers. The measurements were carried out by a technician competent in environmental acoustics and were performed during the ordinary working day through the use of a “Larson Davis” integrator/analyser according to ANSI class I standards. The calibration was performed before and after the execution of the measurements with a “Larson Davis” calibrator conforming to the ANSI class I standards for acoustic calibrators (calibration values within the tolerance limits of 0.5 dB established by the UNI9432: 2011 standard).
Table 1 Noise monitoring in glassware.
The level of daily exposure to noise among workers was evaluated through the following phases: the completion of phonometric surveys of equivalent levels in dB (A) and peak acoustic pressure in dB (C) at workstations; the acquisition of the daily exposure times of workers; and the calculation of daily exposure levels (Lex, 8 h) using specific software (Noise and Vibration Works). Furthermore, to assess the availability of hearing personal protective equipment (PPE) appropriate for workers’ needs, the effectiveness of the PPE in use was verified using special software (Noise and Vibration Works) to calculate the level of daily exposure, which takes into account the attenuation characteristics of the device used.
Equivalent-level measurements were performed in compliance with the UNI 9432: 2011 standard; in particular, the microphone was positioned and oriented to provide the best approximation of the worker's noise exposure without changing the safety conditions and hindering the normal performance of daily work activities.
The type of noise considered is mainly stationary. In accordance with the UNI 9432: 2011 standard, the measurement duration was limited to the time necessary to obtain stabilization within ± 3 dB (A) of the equivalent-level reading of the measurement instrument; in any case, this length of time was not less than 60 seconds. The daily exposure levels were calculated using specific software by entering the values of the equivalent level measured in the workstations and the relative exposure times. Daily exposure levels were calculated by taking into account the use of auricular PPE worn during the activity.
The association between presbycusis and noise was evaluated through the Spearman correlation coefficient and with logistic regression adjusted for age, sex and education.
The noise levels measured by environmental monitoring in the glassware industry are shown in Table 1).
A total of 439 (27%) of the 1611 subjects participating in the study showed the presence of ARHL (Table 2). In the group of 482 subjects professionally exposed to noise for over 10 years, 389 (81%) showed the presence of ARHL.
The presence of ARHL was found in 50 (4%) of the 1129 subjects exposed professionally to noise for less than 10 years or never exposed. In the subgroup of 298 subjects who worked for over 10 years in the glassware industry, ARHL was found in 262 subjects (88% prevalence) (Table 3).
The statistical analysis showed a significant association (p <0.001) between previous occupational exposure and ARHL (OR = 1.09; 95% CI = 1.067-1.124; p = 0.0012) and between exposure to the glassware industry and ARHL (OR = 1.89; 95% CI = 1.78-1.96; p = 0.006) (Table 4).
The results of the environmental monitoring of noise in the glassware industry show that the manufacturing department has the highest noise levels due to the presence of machines in which the hollow glass is printed. Warehouses are areas characterized by negligible noise, levels are well below 80 dB, and workshops are mainly low-noise areas. The attenuation of the noise, guaranteed by the PPE, limits the exposure of the workers to levels below the occupational exposure limit value of 87 dB (A), as established by Italian law (Legislative Decree 81/2008). However, it is necessary to consider that the exposed subjects of the study worked in the glassware industry during the years in which the PPE were not supplied to the personnel in service, were not adequate or were not used. For this reason, it is legitimate to assume that the workers in the glassware industry have been exposed to noise levels that are likely to cause damage to the hearing apparatus.
Our study has some limitations. First, the cross-sectional study design did not allow us to make a comparison with the ISO 1999:2013 standard for estimating noise-induced hearing loss in occupationally exposed workers [40N40 International Organization for Standardization (ISO). Acoustics: Estimation of noise-induced hearing loss (ISO-1999) International Organization for Standardization 2013. Avaiable from: https://www.iso.org/obp/ui/ fr/#iso:std:iso:1999:ed-3:v1:en]. Second, environmental noise monitoring in the glassware industry was conducted many years after the period in which our study population worked. Therefore, we have no direct information about the noise levels or the use and efficiency of PPE during the years in which our exposed group worked.
Table 2 Prevalence of age-related hearing loss.
Table 3 Prevalence of age-related hearing loss in noise-exposed individuals.
Table 4 Logistic regression adjusted for sex, age and education.
The results of our study, even with these limitations, show a higher prevalence of ARHL in the group of occupationally noise-exposed subjects than in the group of non-exposed subjects. Our study is one of the few aiming to evaluate the prevalence of ARHL in a large population occupationally exposed to noise compared with a non-exposed population (1611 subjects). In a recent study on 4988 subjects, Kovalova et al. showed statistically significant differences in hearing loss at various frequencies in various male age groups. The results suggest that males at
occupational risk have a higher auditory threshold than those at no risk. The highest rates of statistically significant differences at frequencies measured by audiometry were seen in males aged 60 to 74 years, followed by the 45 to 59 age group [41Kovalova M, Mrazkova E, Sachova P, et al. Hearing loss in persons exposed and not exposed to occupational noise. J Int Adv Otol 2016; 12(1): 49-54. [http://dx.doi.org/10.5152/iao.2016.1770] [PMID: 27340983] ]. In contrast, the results of another study show no significant differences in hearing decline at any frequency in those from 70 years to 75 years of age between occupational noise-exposed and non-exposed subjects of either gender [42Hederstierna C, Rosenhall U. Age-related hearing decline in individuals with and without occupational noise exposure. Noise Health 2016; 18(80): 21-5. [http://dx.doi.org/10.4103/1463-1741.174375] [PMID: 26780958] ]. In a recent Brazilian study on dance teachers, no statistically significant differences in hearing loss between the participants exposed and those not exposed to occupational noise were found. This finding may have been affected by the small sample size (32 cases and 32 controls) [43Nehring C, Bauer MA, Teixeira A. Study of the hearing threshold of dance teachers. Int Arch Otorhinolaryngol 2015; 19(3): 222-8. [http://dx.doi.org/10.1055/s-0035-1547519] [PMID: 26157496] ]. Another study examining hearing loss in people at risk of exposure to occupational noise (12,055 rail workers) was conducted in Norway by Lie et al. [44Lie A, Skogstad M, Johnsen TS, Engdahl B, Tambs K. The prevalence of notched audiograms in a cross-sectional study of 12,055 railway workers. Ear Hear 2015; 36(3): e86-92. [http://dx.doi.org/10.1097/AUD.0000000000000129] [PMID: 25470371] ]. The findings showed that the audiometric curves in women exposed and those not exposed to occupational noise were virtually unchanged.
In conclusion, the results of our study show a significant association between occupational exposure and ARHL. This association is stronger for those with exposure to the glassware industry. It is therefore possible to hypothesize that occupational exposure to noise may play a role in increasing the prevalence of ARHL in older age. However, in the scientific community, there is still no consensus on the long-term functional effects of noise exposure on ARHL [37Fetoni AR, Picciotti PM, Paludetti G, Troiani D. Pathogenesis of presbycusis in animal models: a review. Exp Gerontol 2011; 46(6): 413-25. [http://dx.doi.org/10.1016/j.exger.2010.12.003] [PMID: 21211561] ]. In a recent literature study, the authors show how repeated short-duration loud-sound overstimulation accelerates the time course of ARHL in an animal model of auditory ageing [45Alvarado JC, Fuentes-Santamaría V, Gabaldón-Ull MC, Juiz JM. Age-Related hearing loss is accelerated by repeated short-duration loud sound stimulation. Front Neurosci 2019 Feb 27; 13(77) eCollection [http://dx.doi.org/10.3389/fnins.2019.00077] ].
In the Framingham study, a combined effect of noise and ageing has been described [45Alvarado JC, Fuentes-Santamaría V, Gabaldón-Ull MC, Juiz JM. Age-Related hearing loss is accelerated by repeated short-duration loud sound stimulation. Front Neurosci 2019 Feb 27; 13(77) eCollection [http://dx.doi.org/10.3389/fnins.2019.00077] ]. They found that elderly men with noise notches in their audiograms had a reduced progression of hearing loss over time at 3 kHz, 4 kHz, and 6 kHz and an accelerated rate of hearing loss in frequency areas adjacent to noise-damaged frequencies, especially at 2 kHz. In men without typical noise notches, this pattern was reversed. This finding could not be reproduced by Lee et al. [50Lee FS, Matthews LJ, Dubno JR, Mills JH. Longitudinal study of pure-tone thresholds in older persons. Ear Hear 2005; 26(1): 1-11. [http://dx.doi.org/10.1097/00003446-200502000-00001] [PMID: 15692300] , 51Lee FS, Matthews LJ, Dubno JR, Mills JH. Threshold changes in older persons: A reply to gates. Ear Hear 2006; 27: 92. [http://dx.doi.org/10.1097/01.aud.0000194514.68129.1a] ].
Most of these studies are based on single noise exposure or short-term noise stimulation protocols, but humans are exposed daily to multiple loud sounds, so additional research is needed to better recreate these noise conditions.
In the future, major repercussions can be expected because while occupational noise tends to decrease in developed countries, it remains a major public health problem worldwide [52Śliwińska-Kowalska M, Zaborowski K. WHO environmental noise guidelines for the European region: A systematic review on environmental noise and permanent hearing loss and tinnitus. Int J Environ Res Public Health 2017; 14(10)E1139 [http://dx.doi.org/10.3390/ijerph14101139] [PMID: 28953238] ]. The population groups at risk are mostly teenagers and young adults, especially due to the use of personal portable audio devices, such as smartphones and MP3 players [23Daniel E. Noise and hearing loss: a review. J Sch Health 2007; 77(5): 225-31. [http://dx.doi.org/10.1111/j.1746-1561.2007.00197.x] [PMID: 17430434] ], which represent a long-term potential health risk for the development of premature presbycusis with all its consequences.
LIST OF ABBREVIATIONS
= Age-Related Hearing Loss;
= Noise-Induced Hearing Loss;
= Identification of Synthetic Sentences with Ipsilateral Competing Message;
= Personal Protective Equipment.
LV, DC and RS conceived and designed the work; DC, LDM and AC performed the work; DC, RS analysed the data and interpreted the results; and LV, DC, LDM, AC, ESSC, FM, FB and DMC wrote and revised the manuscript. All authors read and approved the final manuscript.
ETHICAL APPROVAL AND CONSENT TO PARTICIPATE
Ethical approval is not necessary because all medical and instrumental examinations were performed according to Italian law concerning the protection of workers exposed to occupational risks (D.Lgs. 81/2008).
HUMAN AND ANIMAL RIGHTS
This study did not involve experiments on humans or animals.
CONSENT FOR PUBLICATION
Informed and written consent was obtained from all participants. All subjects were informed that data from the research protocol would be treated in an anonymous and collective way, with scientific methods.
AVAILABILITY OF DATA AND MATERIALS
The data that support the findings of this study are available from the corresponding author [L.V], upon reasonable request.
CONFLICT OF INTEREST
The authors declare no conflict of interest, financial or otherwise.
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