Transcript noise-induced hearing loss in small-scale industries

EP617
NOISE-INDUCED HEARING LOSS IN SMALLSCALE INDUSTRIES IN POKHARA, NEPAL:
A CROSS-SECTIONAL PREVALENCE STUDY
Michael Smith1, Tim Robinson2, Joshua Whittaker2,
Aanand Acharya3, George Dowswell4, Devesh Singh5
1 ENT
2
Department, Worcestershire Royal Hospital, UK
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
INTRODUCTION
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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.
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
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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
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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
Withdrew
Consent
Included
n=122
n=359
n=6
Lost to Follow Up
n=28
Proceeded to
Audiometry
n=331
Excluded after
Audiometry
n=4
Final Dataset
n=327
Metal
Wood
n=99
Hotel
n=124
n=104
RESULTS - Demographics
Demographic
Data
Hotel
Workers
Metal
Workers
Wood
Workers
Difference
(Kruskal-Wallis
or chi-squared)
n
104
99
124
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Age – median
years (IQR)
26.5
(21−35)
24
(21−38)
25
(20−36)
Non-significant
P= 0.854
Gender – %
males
76.92
98.99
100.00
Significant
P<0.001
34.62
48.48
39.52
(0, 0−0.40)
(0, 0−0.95)
(0, 0−0.18)
Significant
P= 0.003
4
(2−12)
4
(1.5−12)
6
(2−15)
Non-Significant
P=0.191
Smoking – %
(median packyears, IQR)
Time in
occupation –
median years
(IQR)
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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
NIHL
Difference
prevalence
(Chi-squared)
(%)
Population
n
Hotel Workers
104
5.05
Metal Workers
99
35.35
Hotel Workers
104
5.05
Wood Workers
124
27.37
Odds Ratio
(95% CI)
Significant
P<0.001
17.83
(5.53−57.51)
Significant
P<0.001
11.46
(3.68−35.70)
RESULTS - continued
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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).
Average Hearing Threshold (0.5, 1, 2, 4kHz) (dBHL)
60
Hotel Workers
Metal Workers
Wood Workers
50
40
R² = 0.2505
30
R² = 0.1474
R² = 0.2559
20
10
0
10
20
30
40
50
Age (Years)
60
70
Plot of average hearing threshold against age, showing
increased hearing thresholds in noise-exposed groups
DISCUSSION
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As expected, occupational noise exposure, hearing thresholds and
NIHL prevalence significantly higher in metal and wood industries.
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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 powercuts, 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.