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