Deterioration of noise-induced hearing loss among bottling factory workers

Audiometric data analysis for prevention of noise-induced hearing loss: A new approach

Compliance with noise regulations in the past three decades has significantly reduced workplace noise exposures, particularly in the loudest industries and occupations. However, the overall effectiveness of hearing conservation programs in preventing occupational noise-induced hearing loss remains uncertain and unquantified, while the incidence and cost of occupational hearing loss remain inexplicably high. This review/commentary critically explores this paradox by examining why the billions of annual audiograms conducted worldwide have not been aggregately utilized or applied to predict early NIHL in groups of workers or to measure the efficacy of exposure controls. Principal contributory reasons include regulation of noise as a safety standard rather than as a health standard, the inherent complexity of audiometric data, and the lack of a standardized method of interpretation for audiograms. The unsuccessful history of efforts to develop and adopt methods and tools to analyze aggregate audiometric data is described. Consequently, the Standard Threshold Shift-a regulatorily defined, lagging indicator of individual, irreversible hearing loss that is not an effective preventive metric-remains the de facto standard of care. A population-based Best Practices approach is proposed to leverage the raw audiometric data already available and turn it into actionable data for effective secondary prevention to strategically manage and reduce occupational hearing loss risk. This approach entails statistical methods and information management tools necessary to transform audiometry from a compliance-driven, individual screening test with limited preventive capability into a medical surveillance process directly linked to aggregate corrective and prevention actions.

The prevalence and global burden of hearing loss in 204 countries and territories, 1990-2019

We aimed to describe the global prevalence and temporal trends of hearing loss. We collected detailed information of hearing loss from the Global Burden of Disease study between 1990 and 2019. Average annual percentage changes (AAPCs) in hearing loss age-standardized prevalence rate (ASPR), by sex, region, and category, were calculated to quantify the temporal prevalence trends. Globally, the prevalent cases of hearing loss increased from 7514.97×10⁵ in 1990 to 14566.62×10⁵ in 2019, and the ASPR increased from 173.33×10² per 100,000 in 1990 to 177.56×10² per 100,000 in 2019. The years lived with disability (YLDs) increased from 220080.97×10² in 1990 to 402353.05×10² in 2019. The AAPC was 83.27 (95% CI 70.66, 95.88) ×10^-3 in prevalence and -72.87 (95% CI -92.18, -53.56) ×10^-3 in YLDs. Significant correlations of AAPCs with ASPR (r=-0.60, p<0.001), and age-standardized YLD rate (r=-0.43, p=0.0012 for YLD<455, r=0.32, p<0.001 for YLD≥455) were detected. The YLDs of hearing loss owing to occupational noise (HLOON) increased from 39334.39 (95% UI 26881.04, 55999.67) ×10² in 1990 to 70014.49 (98% UI 47605.62, 100593.43) ×10² in 2019, and the increasing AAPC was observed for females and aged between 15 and 49 years old in global and most regions. The age effect was under zero in 7 age groups, the period effect of hearing loss prevalence was increasing and the birth cohort effect was decreasing with the time advance. The number of cases and ASPR of hearing loss in the world is still growing. Efforts to control hearing loss, especially HLOON, are imminent.

Kola nut from Cola nitida vent. Schott administered to pregnant rats induces histological alterations in pups' cerebellum

Kola nut (from Cola nitida) is popular in Nigeria and West Africa and is commonly consumed by pregnant women during the first trimester to alleviate morning sickness and dizziness. There is, however, a dearth of information on its effects on the developing brain. This study, therefore, investigated the potential effects of kola nut on the structure of the developing neonatal and juvenile cerebellum in the rat. Pregnant Wistar rats were administered water (as control) or crude (aqueous) kola nut extract at 400, 600, and 800 mg/kg body weight orally, from pregnancy to day 21 after birth. On postnatal days 1, 7, 14, 21 and 28, the pups were weighed, anaesthetised, sacrificed and perfused with neutral buffered formalin. Their brains were dissected out, weighed and the cerebellum preserved in 10% buffered formalin. Paraffin sections of the cerebellum were stained with haematoxylin and eosin for cerebellar cytoarchitecture, cresyl violet stain for Purkinje cell count, Glial Fibrillary Acidic Protein (GFAP) immunohistochemistry (IHC) for estimation of gliosis, and B-cell lymphoma 2 (Bcl-2) IHC for apoptosis induction. The kola nut-treated rats exhibited initial reduction in body and brain weights, persistent external granular layer, increased molecular layer thickness, and loss of Bergmann glia. Their Purkinje cells showed reduction in density, loss of dendrites and multiple layering, and their white matter showed neurodegeneration (spongiosis) and GFAP and Bcl-2 over-expression, with evidence of reactive astrogliosis. This study, therefore, demonstrates that kola nut, administered repeatedly at certain doses to pregnant dams, could disrupt normal postnatal cerebellar development in their pups. The findings suggest potential deleterious effects of excessive kola nut consumption on human brain and thus warrant further studies to understand the wider implications for human brain development.

Socio-economic disparity in the global burden of occupational noise-induced hearing loss: an analysis for 2017 and the trend since 1990

OBJECTIVES

To evaluate socio-economic disparity in the global burden of occupational noise-induced hearing loss (ONIHL) using disability-adjusted life-years (DALYs).

METHODS

The numbers of DALYs due to ONIHL, age-standardised DALY rates and national human development index (HDI) data from 1990 to 2017 were collected. The relationship between the age-standardised DALY rates and the 2017 HDI was analysed. A concentration index (CI) and a relative index of inequality (RII) were calculated to evaluate the trend in socio-economic disparity in the burden of ONIHL for the period 1990-2017.

RESULTS

From 1990 to 2017, the global DALYs due to ONIHL increased from 3.3 to 6.0 million, with the highest growth occurring in low-income countries (110.7%). Age-standardised DALY rates due to ONIHL were negatively associated with the HDI (β = -0.733, p<0.001), and these rates were significantly higher in countries with a lower HDI. From 1990 to 2017, the trend in between-country inequality was flat with little fluctuation, the CIs stayed near -0.17, and the RIIs remained near 0.35.

CONCLUSIONS

Over the past few decades, low-income countries have experienced the most rapid growth in DALYs worldwide. A widening socio-economic disparity has persisted in the global burden of ONIHL, with a higher burden in lower socio-economic countries. These data suggest that more prevention programmes and healthcare services should be provided for developing countries.

Noise Exposure and Hearing Loss among Brewery Workers in Lagos, Nigeria

The health risks of exposure to loud noises are a well-established fact and are widely addressed in modern industries. Yet, in less developed countries, it is thought these hazards receive less attention, both in the workplace and in private life. (1) Background: The aim of this study is to assess the occupational noise exposure in a developing country and identify possible risk groups for whom intervention is needed. (2) Methods: A cross-sectional study was performed among brewery employees in Lagos, Nigeria. Pure-tone audiometry (PTA) was performed, paired with a self-report questionnaire. Personal noise dosimetry (PND) was also performed with an additional group of participants. (3) Results: A total of 458 employees were submitted to PTA. The Packaging and Utilities department reported the largest shifts in hearing thresholds (18 dB [sd = 15] and 16 dB [sd = 15] @4kHz, respectively). No significant effect of department type on auditory health could be found. PND results were obtained from 39 employees. Packaging and Sales were identified as the most exposed departments. (4) Conclusions: A healthy hearing profile was found for a large proportion of the brewery employees (91.7%). However, NIHL (noise-induced hearing loss) proportions specifically among Bottling and Sales employees were elevated.

Apoptosis in the cochlear nucleus and inferior colliculus upon repeated noise exposure

The time course of apoptosis and the corresponding neuronal loss was previously shown in central auditory pathway of mice after a single noise exposure. However, repeated acoustic exposure is a major risk factor for noise-induced hearing loss. The present study investigated apoptosis by terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling (TUNEL) assay after a second noise trauma in the ventral and dorsal cochlear nucleus and central nucleus of the inferior colliculus. Mice [Naval Medical Research Institute (NMRI) strain] were noise exposed [115 dB sound pressure level, 5-20 kHz, 3 h) at day 0. A double group received the identical noise exposure a second time at day 7 post-exposure and apoptosis was either analyzed immediately (7-day group-double) or 1 week later (14-day group-double). Corresponding single exposure groups were chosen as controls. No differences in TUNEL were seen between 7-day or 14-day single and double-trauma groups. Interestingly, independent of the second noise exposure, apoptosis increased significantly in the 14-day groups compared to the 7-day groups in all investigated areas. It seems that the first noise trauma has a long-lasting effect on apoptotic mechanisms in the central auditory pathway that were not largely influenced by a second trauma. Homeostatic mechanisms induced by the first trauma might protect the central auditory pathway from further damage during a specific time slot. These results might help to understand the underlying mechanisms of different psychoacoustic phenomena in noise-induced hearing loss.

Noise Exposure and Self-reported Hearing Impairment among Gas-fired Electric Plant Workers in Tanzania

Background:

Gas-fired electric plants are equipped with heavy machines, which produce hazards including noise pollution. Exposure to high level of noise of above 85dB(A) is known to bring about Noise-Induced Hearing Loss (NIHL). This study aimed to assess noise exposure level and reported prevalence of noise-induced hearing loss among workers in gas-fired electric plants.

Material and Methods:

This cross-sectional study was conducted in three gas-fired electric plants in Dar es Salaam (Plant A, Plant B and Plant C) from July to August 2017. A noise logging dosimeter was used to measure personal noise exposure level. A questionnaire was used to collect information on managerial factors, individual factors, socio-demographic factors and history of the participants. A short screening validated questionnaire was used to obtain noise exposure score. Frequency distribution, Chi-square test and Regression analyses were done using SPSS version 20.

Results:

One hundred and six participants were involved in the study. Noise exposure level among gas-fired electric plant workers was above 85dB(A), n = 37. The equivalent sound level (LAeq) measured over 8 hours was (98.6 ± 9.7) dB(A). The mean noise peak level was (139.5 ± 9.4) dB(A). Plant C had higher mean noise exposure level (TWA) of (96.9 ± 5.1) dB(A) compared to plant B 96.4 ± 3.7dB(A) and plant A 78.7 ± 11.9dB(A). Participants in both operation and maintenance had higher equivalent sound level (LAeq) measured over eight hours of 101.980 ± 3.6dB(A) compared to maintenance alone 98.5 ± 12.4dB (A) or operation 97.7 ± 8.8dB (A). Proportion of participants with reported hearing loss was 57(53.8%) where 44(41.5%) participants reported difficulty hearing people during conversations. Hearing protective devices (HPDs) were reported to be used by a majority, 101(95.3%).

Conclusion:

Workers in gas-fired plants are exposed to high noise levels that could damage their hearing. Hearing conservation programs should be established and maintained in this work environment.

Respiratory Health Status of Workers in a Bottling Factory in Benin City, Nigeria

Introduction: There is a paucity of data on the respiratory health status of workers in bottling factories in Benin City, Nigeria. Such data will help to drive future studies and influence policy development on occupational health and safety in the country. This study assesses the respiratory symptoms and spirometric indices of exposed workers and controls. Methods: Respiratory symptoms and spirometric parameters of 18 workers on routine mandatory annual lung screening were assessed using the modified MRC (Medical Research Council) questionnaire and spirometer respectively, according to the European Respiratory Society and American Thoracic Society (ERS/ATS) guidelines. Results: The mean age of workers was 35.1 ± 6.7 years. Workers and controls were similar in age, sex, BMI (Body Mass Index) and health status (p > 0.05). Respiratory symptoms were significantly higher among workers compared to controls. Overall, the result was statistically significant in the variables of wheeze in a smoky or dusty environment, presence of at least one respiratory symptom, better symptoms at weekends and better symptoms during holidays (p < 0.05). In particular, 6 (33.3%) exposed workers had wheeze in a smoky or dusty environment, 9 (50.0%) exposed workers reported at least one respiratory symptom compared with 2 (11.1%) controls, 5 (27.8%) had better symptoms at weekends, and 7 (38.9%) had better symptoms at holidays (p < 0.05). Generally, the reported frequency of respiratory symptoms among exposed workers were: cough (22.2%), sputum production (5.6%), breathlessness (11.1%) and wheeze (44.4%). Similarly, workers had significantly lower spirometric indices than controls, particularly in forced expiratory volume in 1 s (FEV₁), FEV₁/forced vital capacity (FVC) ratio and forced expiratory flow between 25% and 75% of FVC (FEF 25–75%) measurements. Conclusions: This study provides evidence of adverse respiratory health effects among bottling factory workers which requires further investigation.

[Noise-induced neurodegeneration in the central auditory pathway : An overview of experimental studies in a mouse model]

BACKGROUND

A noise trauma induces central nervous system pathologies, which generate deficits in hearing and perception of sound.

OBJECTIVE

Are degenerative mechanisms in the central auditory system a direct impact of overstimulation or an effect of acoustic deprivation?

MATERIALS AND METHODS

Detection of cell death in a mouse model of noise-induced hearing loss at different times after single or repeated noise exposure.

RESULTS

A single noise exposure (3 h, 115 dB SPL, 5-20 kHz) induces acute (≤1 day) and long-term (observation period 14 days) degeneration, particularly in subcortical structures. Repeated noise trauma is followed by pathologies in the auditory thalamus and cortex.

CONCLUSION

Noise has a direct impact on basal structures of the central auditory system; a protection of cortical areas is possibly due to inhibitory neuronal projections. Degenerative mechanisms in higher structures of the pre-damaged system point to an increased impairment of complex processing of acoustic information.

Follow-up of latency and threshold shifts of auditory brainstem responses after single and interrupted acoustic trauma in guinea pig

Thresholds of auditory brainstem responses (ABRs) are widely used to estimate the level of noise-induced hearing loss or the level of acquired resistance to acoustic trauma after repeated exposures, i.e., the "toughening" effect. Less is known about ABR latencies and their relation to threshold changes. Guinea pigs were exposed to a traumatic pure tone at 5 kHz, 120 dB SPL, as either single (2 h, 4 h) or repeated (1 h every 48 h, four times) sessions. Thresholds and latencies of ABRs were monitored up to 45 days following the acoustic trauma. We show that latencies are prolonged in the case of large temporary threshold shifts observed in the days following trauma. The latency shift decreases after several repeated exposures, then stabilizes, similar to thresholds, suggesting that the "toughening" effect also applies to latencies. Permanent latency shift is usually very small compared to the permanent threshold shift. This effect could produce a recovery in the ability to process auditory information through the precise timing of neuronal events. Our study indicates that when estimated at suprathreshold stimulation level (70 dB SPL), latency provides complementary information to the sole threshold.