Download 1724 1. Hearing in young men – The influence of military noise

Prevalence values of hearing impairment and self-assessed
auditory symptoms among young Swedish men, 1971 - 2005
Per Muhr, Ulf Rosenhall
Presenter: Ulf Rosenhall, MD, PhD
Department of Clinical Science, Intervention and Technology,
Karolinska Institutet, and the Department of Audiology,
Karolinska University Hospital, Stockholm, Sweden
The Swedish Armed Forces, The Occupational Health
Center at the Garrison of Halmstad, Sweden
The Swedish Armed Forces have relied on a conscript system where all
young men, liable for compulsory military service, constitute the
fundament - recently also voluntary for women
The conscript system is
phased out in July 2010
after almost 200 years
The conscript system
was introduced in 1811
1914
1866
2004
All servicemen who are drafted undergo
medical examinations, including screening
audiometry at:
1) Conscription at age 18 years
2) Reporting to service at 18 – 22 years of age
3) Discharge after 260 days of military service
4) Any occasion during military service, if indicated
All medical data are filed and available to research after ethical
approval
There is a possibility to add questionnaires for quality assurance
Prevalence values of mild – moderate hearing loss in
six age cohorts of 18-year old men from 1971 to 1995
Numbers of participants in the study (n: 301 873)
and participation rate
Year of
birth
Year of
conscription
1953
1971
1958
1976
1963
1981
1968
1986
1973
1991
1977
1995
1953 – 1977 1971 - 1995
Conscripts
with
audiogram
52 859
50 676
54 325
51 757
49 752
42 504
301 873
Participation
rate, %
92.9
93.0
92.2
88.6
86.5
82.0
91.1
Prevalence of hearing loss at discrete frequencies (0.5 to 6 kHz), in
the total material 1971 - 1995. Threshold elevations 25 – 30 dB HL,
35 – 40 dB HL, and ≥45 dB HL. Left ear
Prevalence values of
threshold elevations
Prevalence, %
A, Left ear
8
7
6
5
4
3
2
1
0
• 13.1 % All threshold
>=45 dB
35 - 40 dB
25 - 30 dB
0,5
1
2
3
Frequency
4
6
• 11.9 % High frequency
threshold
• 3.2 % Bilateral high
frequency
thresholds
• 7.5 % Left ear
• 6.2 % Right ear
Development of hearing loss at discrete frequencies
in 18-year old men from 1971 to 1995
10
10
LEFT EAR

8
Percent
RIGHT EAR
8
4kHz


6
6kHz
6

4
4
3kHz
2kHz
1kHz
2
2
0
0
1971
1976
1981
1986
1991
Year of Conscription
1995
1971
1976
1981
1986
1991
1995
Year of Conscription
High frequency hearing loss decreased from 15.3 % in 1971 to
8.3 % in 1981, and increased to 14.3 % in 1995 above all at 6 kHz
0.5kHz
Prevalence of at least one threshold 25 dB HL
in one or both ears at 3, 4 or 6 kHz, %
18
16
Prevalence %
14
12
>= 45 dB HL
10
35-40 dB HL
8
25-30 dB HL
6
4
2
0
1971
1976
1981
1986
1991
1994
Year
>40 dB HL the prevalence decreased from 3.8% in 1971 to 1.9% in 1995
Hearing in young men – The influence of military
noise exposure
Peak level
156 dB SPL
Peak level 175-184 dB SPL
103-107 dB(A)
Two groups of conscripts
studied 1999 – 2000,
and 2002 - 2005
Design: prospective,
longitudinal and
cross-sectional studies
n: 1724
1. Hearing in young men – The influence of military
noise exposure
• To investigate the incidence and the relative risk of hearing
deterioration during primary military service among military
servicemen with different noise exposure
• To investigate if those of the conscripts who had a mild hearing
loss when reporting for training had an increased risk of hearing
decline compared to those with normal hearing
747 servicemen, aged 20 - 24 years, studied 1999 - 2000
291 military engineers, 252 infantry men, 204 artillery men
Subgroup: 95 conscripts (12.7%) who had a mild hearing
loss at reporting for training
Comparison group: 138 men followed from the
conscription to reporting for training
Incidence of significant threshold shift (STS), risk ratio
(RR) and 95% confidence interval (CI) relative the
comparison group
Group
Total
Incidence of STS,
Incidence of
RR
CI, 95
number
number
STS, %
Comparison group
138
4
2.9
Engineers
291
11
3.8
1.3
0.4-4.0
Infantry
252
13
5.2
1.8
0.6-5.4
Artillery
204
35
17
5.9
2.2-16
Total
747
59
7.9
2.7
1.0-7.4
%
Incidence of STS, risk ratio (RR) and 95% confidence
interval (CI) relative the comparison group and military
servicemen with different noise exposure
Group
Total
Incidence of STS,
Incidence of STS,
RR
CI, 95 %
number
number
%
Comparison group
138
4
2.9
Engineers, command and
131
3
2.3
0.8
0.2-3
Engineers, builders
160
8
5.0
1.7
0.5-5.6
Infantry, command and support
135
6
4.4
1.5
0.4-5.3
Infantrymen
117
7
6.0
2.1
0.6-6.9
Artillery, command and support 135
19
14.1
4.9
1.7-13.9
Artillery, howitzer platoons
16
23.2
8.0
2.8-23.0
support
69
Incidence of STS, RR and CI among the conscripts
with and without a mild hearing loss at reporting for
training relative the comparison group.
RR
CI, 95 %
6.6
2.2
0.8 – 6.0
17
6.8
2.1-29
Hearing thresholds at
Total
Incidence of
Incidence of
reporting
number
STS, number
STS, %
Comparison group
138
4
2.9
All freq. 20 dB HL or
652
43
95
16
better
At least one freq. >20
dB HL
Conclusions
1. Hearing in young men – The influence of military
noise exposure
Hearing decline:
Controls: 2.9%; Military servicemen: 7.9%
Conscripts with HI at reporting to service: 17%
From 2.3% to 23.2% related to military noise
exposure
There still occurs hearing deterioration above all in the artillery
in spite of the military hearing preservation program
Those of the conscripts who already at reporting for training
had a mild hearing loss seemed to be at higher risk
The study resulted in stricter military safety rules in 2000
2. Hearing in young men – The influence of military
noise exposure
• To estimate prevalence and incidence values of and relations
between auditory symptoms, slight hearing loss, and noise
exposure before and during primary military service
• To study prognostic values of tinnitus and ototraumatic
indicators on auditory deterioration during military service
• To study knowledge, attitude to and efficacy of the present
Hearing Conservation Program in the Swedish Armed Forces
839 servicemen, aged 19 - 22 years, studied longitudinally
2002 – 2005 at reporting to training and at
the end of the service. Length of military
service: 260 days (7.5 - 11 months)
Military units: Anti-aircraft regiment;
Artillery regiment; Armoured regiment
Methods: screening audiometry and
questionnaires
2. Hearing in young men
The influence of military
noise exposure
Reporting
Discharge
Hearing problems
20.7 (1.7)
28.4 (3.3)
Hearing probl. in noise
35.7 (2.3)
37.6 (4.8)
Tinnitus
23.2 (3.4)
31.9 (4.8)
Sensitive to noise
15.5 (1.9)
18.9 (2.2)
Conscription
Reporting
Discharge
0.5 – 8 kHz
6.3
14.5
24
3, 4, 6 kHz
2.6
7.4
12.3
8 kHz
3.5
9.8
14.8
Self-assessed auditory
symptoms (per cent)
Prevalence values
(often always)
Hearing impairment
<20 dB HL
(per cent)
Prevalence values
2. Hearing in young men – The influence of military
noise exposure
• High prevalence values of self-assessed problems and of noise exposure
• Risk factors for tinnitus: Tinnitus/TTS after noise exposure;
Active music performance; Frequent otitis media in childhood;
History of concussion and loss of consciousness
• Elevated incidence of hearing decline during military service,
especially for those who reported acoustic accidents
• Auditory symptoms and hearing loss are common at reporting among
the group (4%) who interrupted the training because of hearing
problems
The risk of hearing decline during military service has decreased
(RR: 2.7 in the late 90:ies to 1.8) but has not been eliminated
Conclusions and Summary
Audiometric data collected by
the Swedish Armed Forces
during the last 40 years have been
used to study the epidemiology of
mild - moderate hearing loss
in young men
Long-term fluctuations of prevalence values of pure tone threshold
elevations have been demonstrated, with increasing prevalence of
high frequency hearing loss to the mid 90:ies
Military service implies a risk for hearing impairment and auditory
symptoms (e.g. tinnitus). The risk is related to the noise levels during
military training
Improvements of the Hearing Conservation Program for the Swedish
Armed Forces, now with professional personnel, are suggested
Research group
P Muhr
U Rosenhall
PA Hellstrom
B Mansson
B Hagerman
F Rasmussen