Department of Clinical Science, Intervention and Technology, Karolinska Institutet, and the Department of Audiology,
Karolinska University Hospital, Stockholm, SwedenThe Swedish Armed Forces, The Occupational Health
Center at the Garrison of Halmstad, Sweden
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
The Swedish Armed Forces have relied on a conscript system where allyoung men, liable for compulsory military service, constitute the
fundament - recently also voluntary for women
The conscript systemwas introduced in 1811
The conscript system isphased out in July 2010after almost 200 years
1866
1914
2004
All servicemen who are drafted undergo medical examinations, including screening audiometry at:
1) Conscription at age 18 years2) 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
Year of birth
Year of conscription
Conscripts with
audiogram
Participation rate, %
1953 1971 52 859 92.9 1958 1976 50 676 93.0 1963 1981 54 325 92.2 1968 1986 51 757 88.6 1973 1991 49 752 86.5 1977 1995 42 504 82.0
1953 – 1977 1971 - 1995 301 873 91.1
Numbers of participants in the study (n: 301 873) and participation rate
Prevalence values of mild – moderate hearing loss in six age cohorts of 18-year old men from 1971 to 1995
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
A, Left ear
0
1
2
34
5
6
7
8
0,5 1 2 3 4 6
Frequency
Pre
vale
nce
, %
>=45 dB
35 - 40 dB
25 - 30 dB
Prevalence values of threshold elevations
• 13.1 % All threshold• 11.9 % High frequency
threshold• 3.2 % Bilateral high
frequency thresholds
• 7.5 % Left ear• 6.2 % Right ear
0
2
4
6
8
10
Per
cen
t
1971 1976 1981 1986 1991 1995
Year of Conscription
LEFT EAR
0
2
4
6
8
10
1971 1976 1981 1986 1991 1995
Year of Conscription
0.5kHz
1kHz
2kHz
3kHz
4kHz
6kHz
RIGHT EAR
Development of hearing loss at discrete frequencies in 18-year old men from 1971 to 1995
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
2
4
6
8
10
12
14
16
18
1971 1976 1981 1986 1991 1994
Year
Pre
vale
nce
% >= 45 dB HL
35-40 dB HL
25-30 dB HL
Prevalence of at least one threshold 25 dB HL in one or both ears at 3, 4 or 6 kHz, %
>40 dB HL the prevalence decreased from 3.8% in 1971 to 1.9% in 1995
Peak level156 dB SPL
103-107 dB(A)
Peak level 175-184 dB SPL
Hearing in young men – The influence of military noise exposure
Two groups of conscriptsstudied 1999 – 2000, and 2002 - 2005Design: 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
number
Incidence of STS,
number
Incidence of
STS, %
RR CI, 95
%
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
number
Incidence of STS,
number
Incidence of STS,
%
RR CI, 95 %
Comparison group 138 4 2.9
Engineers, command and
support
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 69 16 23.2 8.0 2.8-23.0
Incidence of STS, RR and CI among the conscripts with and without a mild hearing loss at reporting for
training relative the comparison group.
Hearing thresholds at
reporting
Total
number
Incidence of
STS, number
Incidence of
STS, %
RR CI, 95 %
Comparison group 138 4 2.9
All freq. 20 dB HL or
better
652 43 6.6 2.2 0.8 – 6.0
At least one freq. >20
dB HL
95 16 17 6.8 2.1-29
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
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
The study resulted in stricter military safety rules in 2000
Conclusions1. Hearing in young men – The influence of military
noise exposure
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
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
Hearing impairment<20 dB HL(per cent)Prevalence values
Self-assessed auditory symptoms (per cent)Prevalence values(often always)
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
2. Hearing in young men – The influence of military noise exposure
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 trainingImprovements of the Hearing Conservation Program for the Swedish Armed Forces, now with professional personnel, are suggested
Research group
P MuhrU RosenhallPA HellstromB ManssonB HagermanF Rasmussen