NOISE-INDUCED HEARING LOSS IN SMALL-SCALE INDUSTRIES IN POKHARA, NEPAL:

A CROSS-SECTIONAL PREVALENCE STUDY

Michael Smith1, Tim Robinson2, Joshua Whittaker2, Aanand Acharya3, George

Dowswell4, Devesh Singh5

1 ENT Department, Worcestershire Royal Hospital, UK2 College of Medical and Dental Sciences, University of Birmingham, UK

3 ENT Department, University Hospitals Birmingham, UK4 Primary Care Clinical Sciences, University of Birmingham, UK5 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.

AimTo 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 (LAeq) measured over 1 hour and

extrapolated to an 8-hour working day (LAeq,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: Questionnaire Stage 2: Otoscopy Stage 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)

n 104 99 124 -

Age – median years (IQR)

26.5 (21−35)

24(21−38)

25(20−36)

Non-significantP= 0.854

Gender – % males 76.92 98.99 100.00 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)

SignificantP= 0.003

Time in occupation – median years

(IQR)

4 (2−12)

4(1.5−12)

6(2−15)

Non-SignificantP=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

Population nNIHL

prevalence (%)

Difference (Chi-squared)

Odds Ratio (95% CI)

Hotel Workers 104 5.05 SignificantP<0.001

17.83(5.53−57.51)Metal Workers 99 35.35

Hotel Workers 104 5.05 Significant P<0.001

11.46 (3.68−35.70)Wood Workers 124 27.37

• 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).

• LAeq,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

10 20 30 40 50 60 700

10

20

30

40

50

60

R² = 0.147441765481942

R² = 0R² = 0Hotel WorkersLinear (Hotel Workers)Metal Workers

Age (Years)

Aver

age

Hear

ing

Thre

shol

d (0

.5, 1

, 2, 4

kHz)

(dBH

L)

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 LAeq,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.