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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