Presentation on theme: "NOISE-INDUCED HEARING LOSS IN SMALL- SCALE INDUSTRIES IN POKHARA, NEPAL: A CROSS-SECTIONAL PREVALENCE STUDY Michael Smith 1, Tim Robinson 2, Joshua Whittaker."— Presentation transcript:
NOISE-INDUCED HEARING LOSS IN SMALL- SCALE INDUSTRIES IN POKHARA, NEPAL: A CROSS-SECTIONAL PREVALENCE STUDY Michael Smith 1, Tim Robinson 2, Joshua Whittaker 2, Aanand Acharya 3, George Dowswell 4, Devesh Singh 5 1 ENT Department, Worcestershire Royal Hospital, UK 2 College of Medical and Dental Sciences, University of Birmingham, UK 3 ENT Department, University Hospitals Birmingham, UK 4 Primary Care Clinical Sciences, University of Birmingham, UK 5 ENT Department, Western Regional Hospital, Pokhara, Nepal EP617
Noise-induced hearing loss (NIHL) is an irreversible sensorineural hearing impairment characterised by high frequency (3−6 kHz) hearing loss. Consequences include social isolation, impaired communication, increased injury risk and reduced productivity for employers. Risk of NIHL increases with magnitude and duration of noise exposure. Regular exposure to >85 dBA considered hazardous to hearing. WHO estimate 16% of adult-onset hearing loss in South-East Asia attributable to occupational noise. INTRODUCTION
NIHL in Nepal Joshi et al. studied environmental NIHL in Kathmandu. Retrospective cohort: cases exposed >70dbA (n=36), controls <55 dBA (n=25). OR=4.2 (4.0 when adjusted for occupational noise). No previous occupational NIHL research identified. Economically active population = 16.6 million. >95% work informally; not covered by occupational health and safety legislation. Substantial proportion at risk of NIHL. Need for research to support generation of noise permissible exposure limit (PEL) legislation.
Aim To assess occupational noise exposure, hearing thresholds and NIHL prevalence in two small-scale industries in Pokhara, Nepal, and compare to non-exposed controls
METHODS AND MATERIALS Cross-sectional prevalence study based in Pokhara, Kaski District. – Conducted between February and April 2012. Convenience sampling of workplaces: − Metal and wood workers (exposed groups). − Hotel workers (control group). Exclusion Criteria Aged <15 years. Working in current occupation <6 months. Current bilateral outer/middle ear pathology. Permanent bilateral hearing loss preceding occupational noise exposure.
Assessment Protocol Noise exposure: Average workplace noise (L Aeq ) measured over 1 hour and extrapolated to an 8-hour working day (L Aeq,8h ) for each participant. All consented individuals received: – Hearing and occupational history questionnaire. – Otoscopy (exclusion/inclusion confirmed by ENT referral where necessary). – Air-conduction audiometry at 0.5, 1, 2 and 4 kHz. Those with a single ear average threshold >25dBHL OR >25dBHL at 4kHz, proceeded to: – Air-conduction audiometry at 3, 6 and 8 kHz. – Bone-conduction audiometry at 1, 2 and 4 kHz. – Masked thresholds where necessary according to British Society of Audiology standards. Peak threshold between 3-6kHz (‘notch configuration’) = NIHL. Stage 1: QuestionnaireStage 2: OtoscopyStage 3: Audiometry
Consent n=487 Met Exclusion Criteria n=122 Included n=359 Proceeded to Audiometry n=331 Final Dataset n=327 Metal n=99 Wood n=124 Hotel n=104 Excluded after Audiometry n=4 Lost to Follow Up n=28 Withdrew Consent n=6
Demographic Data Hotel Workers Metal Workers Wood Workers Difference (Kruskal-Wallis or chi-squared) n10499124- Age – median years (IQR) 26.5 (21−35) 24 (21−38) 25 (20−36) Non-significant P= 0.854 Gender – % males 76.9298.99100.00 Significant P<0.001 Smoking – % (median pack- years, IQR) 34.62 (0, 0−0.40) 48.48 (0, 0−0.95) 39.52 (0, 0−0.18) Significant P= 0.003 Time in occupation – median years (IQR) 4 (2−12) 4 (1.5−12) 6 (2−15) Non-Significant P=0.191 RESULTS - Demographics 67.15% of recruited completed assessment Sample from 17 hotels, 13 metal works and 15 wood works All continuous data non-normal (K-S test) 82.26% had a smoking history of <1 pack-year with 4.28% ≥ 5 pack-years 50.15% aged ≤ 25 years; 89.60% ≤45 years
RESULTS – NIHL Prevalence Populationn NIHL prevalence (%) Difference (Chi-squared) Odds Ratio (95% CI) Hotel Workers1045.05 Significant P<0.001 17.83 (5.53−57.51) Metal Workers9935.35 Hotel Workers1045.05 Significant P<0.001 11.46 (3.68−35.70) Wood Workers12427.37
Significant difference in average hearing threshold distribution between controls and exposed (medians = 11.25 dBHL vs. 17.50 dBHL; P<0.001). Non-significant difference in distribution between exposed groups (medians = metal 16.88 dBHL vs. wood 18.10 dBHL; P=0.403). L Aeq,8h distribution significantly different between controls and exposed (medians = hotel 59.10 dBA, metal 80.56 dBA, wood 85.10 dBA; P<0.001). Noise levels ranged between 51.4−68.6 dBA at hotel sites, 65.3−84.7 dBA at metal sites and 71.2−93.9 dBA at wood sites. All odds ratios generated through binary logistic regression, adjusted for age and time in occupation. All other demographics were non-significant in predicting risk of NIHL. Odds Ratio for risk of NIHL for any exposed vs. control = 13.44 (95% CI= 4.69−38.54). RESULTS - continued
Plot of average hearing threshold against age, showing increased hearing thresholds in noise-exposed groups
DISCUSSION As expected, occupational noise exposure, hearing thresholds and NIHL prevalence significantly higher in metal and wood industries. – Young age distribution and short exposure time may mask true disability associated with NIHL. – Significant differences in smoking level, but low pack-years so unlikely to significantly impact on hearing. Lack of comparable results as previous studies in small-scale workshop industries recruited significantly smaller samples. Industrialisation and a growing economically active population in Nepal likely to put further people at risk. Occupational health and safety guidelines currently provide minimal protection for workers.
Limitations Convenience sampling reduces generalisability of results. Workplace noise assessment did not account for variation in noise exposure levels caused by power- cuts, compromising validity of L Aeq,8h as comparator. Inability of data collection tool to standardise noise exposure and hearing history.
CONCLUSIONS Workers in small-scale metal and wood industries appear to be at significantly higher risk of NIHL, compared to control subjects. There is a need for hearing conservation policies to cover a growing workforce in Nepal. These measures may alleviate the effects of a widespread, yet preventable hearing impairment.
References 1. Concha-Barrientos et al. Occupational noise: assessing the burden of disease from work-related hearing impairment at national and local levels. WHO Environmental Burden of Disease, No 9. Geneva, WHO (2004) 2. Nelson et al. The global burden of occupational noise-induced hearing loss. American Journal of Industrial Medicine (2005) 48(6):446-458 3. Joshi et al. Environmental noise induced hearing loss in Nepal. Kathmandu University Medical Journal (2003) 1(3):177-183 4. International Labour Organisation. Labour and Social Trends in Nepal 2010. Geneva, ILO (2010)
This study was carried out as part of the International Health course at the University of Birmingham, UK. Logistical support was provided by the International Nepal Fellowship. The authors report no conflicts of interest.