1. 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 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

2. 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 was introduced in 1811 The conscript system is phased out in July 2010 after almost 200 years 1866 1914 2004

3. 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

4. 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

5. 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 13.1 % All threshold 11.9 % High frequency threshold 3.2 % Bilateral high frequency thresholds 7.5 % Left ear 6.2 % Right ear

6.     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

7. 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

8. Hearing in young men – The influence of military noise exposure Two groups of conscripts studied 1999 – 2000, and 2002 - 2005 Design: prospective, longitudinal and cross-sectional studies n: 1724

9. 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

10. Incidence of significant threshold shift (STS), risk ratio (RR) and 95% confidence interval (CI) relative the comparison group

11. Incidence of STS, risk ratio (RR) and 95% confidence interval (CI) relative the comparison group and military servicemen with different noise exposure

12. Incidence of STS, RR and CI among the conscripts with and without a mild hearing loss at reporting for training relative the comparison group.

13. 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 Conclusions 1. Hearing in young men – The influence of military noise exposure

14. 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

15. ReportingDischarge Hearing problems20.7 (1.7)28.4 (3.3) Hearing probl. in noise35.7 (2.3)37.6 (4.8) Tinnitus23.2 (3.4)31.9 (4.8) Sensitive to noise15.5 (1.9)18.9 (2.2) ConscriptionReportingDischarge 0.5 – 8 kHz6.314.524 3, 4, 6 kHz2.67.412.3 8 kHz3.59.814.8 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

16. 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

17. 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

18. Research group P Muhr U Rosenhall PA Hellstrom B Mansson B Hagerman F Rasmussen