Estimated Leisure-Time Noise Exposure, Hearing Thresholds, and Hearing Symptoms of Finnish Conscripts

Transcription

1 MILITARY MEDICINE, 171, 2:112, 2005 Estimated Leisure-Time Noise Exposure, Hearing Thresholds, and Hearing Symptoms of Finnish Conscripts Guarantor: Lt Col (Med) Toivonen Contributors: Jaana Jokitulppo, MSc* ; Lt Col (Med) Markku Toivonen, MD ; Erkki Björk, PhD The aim of this study was to set up a statistical measure for determine the total cumulative noise exposure of Finnish conscripts (n 1,054) as a result of leisure-time noise activities. All of the conscripts underwent hearing screening. The conscripts time in noisy activities and their rating of the loudness and estimated noise levels of the activities were used as the predictors in the risk analysis. Self-reported hearing symptoms (i.e., tinnitus, pain in the ear) and hearing loss due to noise exposure were also inquired about. Twenty-seven percent of the conscripts had weekly noise exposure to 85 dba. Approximately 20% of the conscripts had 20 db hearing loss in either ear in the frequency range of 0.5 to 8 khz. The incidence of hearing symptoms seemed to correlate with an increased noise dose. Introduction ccupational noise hazards are well known and legislation O stipulates that noise exposure of 85 to 90 db is a risk to hearing 1,2 when working. The risk limits are mainly related to the risk of hearing loss, and less attention has been paid to noise limits with regard to other hearing symptoms (e.g., tinnitus). The noise levels in certain leisure-time environments can be as high or even higher than noise levels at work. 3 However, the effect of leisure-time noise on hearing is controversial due to the great variety of sound levels encountered in activities and personal tolerance to noise. 4,5 Studies of hearing handicaps among young men starting their military service have concluded that the hearing loss is attributable to exposure to high sound levels during leisure time. 6,7 According to these studies, the prevalence of hearing loss varies by 15 to 18%. In 1990, Borchegrevink 8 even speculated that the incidence of hearing loss would increase to 36% among young military men over the next decade, but clear evidence of this phenomenon is still lacking. All Finnish men are required to report for obligatory military service at the age of 18 years. Approximately 30,000 new conscripts ages 18 to 29 years of age start their military service annually. However, most conscripts are between 19 and 20 years of age, and they represent approximately 80% of their age group. This group is a representative sample for studies on the effect of leisure-time noise exposure on hearing. The general health of conscripts is at its best in the population and most of them have not been exposed to occupational noise. For those that have been exposed to occupational noise, the length of exposure is at most, 1 or 2 years. *Tampere Regional Institute of Occupational Health, P.O. Box 486, FIN Tampere, Finland. Department of Environmental Sciences, University of Kuopio, P.O. Box 1627, FIN Kuopio, Finland. Pori Brigade, Garrison Hospital, P.O. Box 38, FIN Säkylä, Finland. This manuscript was received for review in January The revised manuscript was accepted for publication in December Reprint & Copyright by Association of Military Surgeons of U.S., The aim of this study was to examine the hearing thresholds of the conscripts at the beginning of their conscription in the Pori Brigade in January 2001, to estimate their personal weekly noise exposure levels and their total cumulative noise exposure before starting military service, and to determine the effects of their personal noise exposure on hearing thresholds and selfreported hearing symptoms. Methods Altogether 30,000 conscripts start military service annually, but only 19,000 serve at the same time in Finland. Instead they are divided into two groups of approximately 15,000 each, one group usually starting in January and the other beginning in June. In the Pori Brigade, all 1,213 of the conscripts beginning in January 2001, approximately 8% of the total group of conscripts of 14,867, participated in this study. The conscripts filled out the questionnaires on a voluntary basis as part of their medical examination on arrival and they returned the questionnaire to the medical officer field nurse (in Pori Brigade), who sent the questionnaires to one of the researchers for analysis. The study was carried out using a basic noise exposure questionnaire format developed by Jokitulppo et al. in Some questions were added however on the special characteristics of tinnitus and hearing loss (Fig. 1). The results of the hearing test (personal audiometer) were also added to the questionnaire. All of the conscripts underwent an audiometric examination. Pure tone audiometry (air conduction) was performed using a Micromate 304 Madsen Electronics Screening Audiometer (GN Otometrics, Taastrup, Denmark). The tests were carried out in sound-insulated test rooms (Fin 2200, Audio & Kuulo, Turku, Finland or T-booth, C-A Tegnér AB, Bromma, Sweden). The tested frequencies were 500, 1,000, 2,000, 3,000, 4,000, 6,000, and 8,000 Hz. Hearing loss was defined as thresholds 20 db HL at one or more frequencies in one or both ears according to the following classification: type 1: normal hearing, 20 db or better at each frequency; type 2: mild hearing loss, hearing threshold of 20 db or better in the speech frequencies ( Hz) or a maximum of 40 db at 3 khz or of a maximum of 65 db at 4 khz; type 3: mild hearing loss, hearing threshold of an average better than 20 db in the speech frequencies, but a hearing threshold worse than that used for type 2; or type 4: moderate hearing loss, hearing threshold of an average of 20 db or worse in the speech frequencies. With the use of the Microsoft Excel computer program (version 1997, SR-1, Redmond, Washington), the weekly noise exposure levels (L EX,40h ) were calculated according to the noise energy principle both for each leisure-time activity separately and for all of the leisure-time activities combined (equation 1). The leisure-time noise exposure was calculated using the selfreported duration of exposure in leisure-time noise activities 112

2 Cumulative Noise Exposure of Finnish Conscripts 113 dba. If the used hours of activity were estimated as hours per year, the total sum of the hours per year was divided by 52 for the weekly noise exposure calculations: L Aeq,w LAeq 10*log 10 (T W /T 0 ), (1) where L Aeq,w is the weekly equivalent noise level of the activity; LAeq is the A-weighted sound pressure level of leisure-time activity, from 60 to 100 db; T w is time used (hours) on the activity in weeks; and T 0 is the reference weekly noise exposure of a 40-hour workweek. Some generalizations of noise types were done in this study. All of the leisure-time activities were regarded as the steady type of noise with the equivalent levels of 60 to 100 db for all of the activities, as well as impulse type of noise sources such as fireworks and firearms. The cumulative (lifetime) noise exposure was also calculated by using the self-reported total time of years spent in each activity and in all of the activities combined (equation 2). L Aeq,cum LAeq,w 10*log 10 T year, (2) where T year is time used on the activity in years. Cumulative noise exposure of each subject was compared to calculated cumulative hearing loss limits for an exposure level of 85 dba over 40 years, with 101 dba, exposure level of 80 dba over 40 years with 96 dba; and for 75 dba over 40 years with 91 dba (by equation 2). If the total number of years of exposure was not reported, 1 year was used in the calculations. Basic statistical analyses were used to describe the data. The limit for statistical significance was set at All of the statistical analyses were carried out with the SPSS program (version 11.5, SPSS, Chicago, Illinois). Fig.1. Hearing loss questionnaire. (per week or per year) and the subjective estimated loudness levels (from 1 to 5) of each activity. The rating of 1 to 5 was transformed into A-weighted equivalent sound pressure levels with the following: 1 60, 2 70, 3 80, 4 90, and Results Altogether 1,189 (response rate 98%) questionnaires were returned in this study and 1,054 were accepted and 135 were rejected because of missing information or overestimations of the time used on activities. The conscripts were between the ages of 19 and 27 years (all males). Their average age was 19.9 years and 90% were between 19 and 20 years of age. The most frequent activities were watching television, listening to a home stereo, and going to night clubs and pubs (Table I). The most time was also spent on watching television, listening to a home stereo, and using tools inside and outside the house (Table I). The average total sum of spent hours per week for all activities was 43.1 hours (range, hours), with a median of 39.0 hours. The average total sum of spent hours per year was 64.0 hours (range, 0.5 2,020 hours), with a median of 26.0 hours. The conscripts considered festivals and concerts, shooting firearms, playing in a band, and using tools indoors and outdoors to be the loudest leisure-time activities. The calculated weekly noise exposure medians of the different activities varied from 50 to 80 dba. The highest exposure levels were found for noisy work, using noisy tools indoors, playing in a band, and going to nightclubs and pubs. The median and average for the total weekly noise exposure was 80 dba (range, dba). For total lifetime noise exposure, both the median and average was 82 dba (range, dba).

3 114 Cumulative Noise Exposure of Finnish Conscripts TABLE I ATTENDANCE AND DURATION OF ATTENDANCE (AVERAGE HOURS) OF DIFFERE NT LEISURE-TIME ACTIVITIES Time Spent Activity Percentage of Conscripts Per Week (hours) Per Year (hours) Watching television Listening to a home stereo/ radio Going to nightclubs or pubs Watching movies/plays Playing computer games Attending musical festivals Exposure to other impulse noise, fireworks Listening to a home stereo/ radio headphones Attending indoor sports events Listening to a portable stereo Noisy work Using noisy tools indoors Using noisy tools outdoors Practicing a musical instrument Shooting firearms Playing in a band or orchestra Participating in motor sports Exercising to the accompaniment of music Altogether 27% of the conscripts were exposed weekly to noise levels over the 85 dba risk limit for hearing handicap. 10 Fifty percent of the conscripts were exposed weekly to noise levels over 80 dba and for 69% the noise levels were above 75 dba. A cumulative (the lifetime) noise exposure of 101 dba (85 db with 40 years) was reached by 2% of conscripts, 8% had a corresponding value of 96 dba (80 dba for 40 years), and 19% was 91 dba ( 75 dba for 40 years). Altogether 67% of conscripts experienced tinnitus sometimes during noise exposure and for 8% tinnitus occurred often or continuously (Table II). Tinnitus due to some other reason than noise exposure was experienced sometimes by 28% and often or continuously by 1%. The degree of tinnitus was described as moderate by 71% of the conscripts and as annoying or very annoying by 6%. Bilateral tinnitus was reported by 50%, whereas there was tinnitus in the middle of the head for 8%, and it was unilateral for 14%. Temporary hearing loss due to noise exposure occurred sometimes in 45% and often or continuously in 2%. Sixty-five percent of the conscripts described annoyance due to noise exposure sometimes, whereas 4% claimed it occurred often or continuously. Sound distortion was a problem sometimes for 29% and often or continuously for 1%. The average noise levels were calculated for each hearing symptom group (Table III). The estimated weekly noise dose was statistically significantly greater for the groups with tinnitus or temporary threshold shift (TTS) (both p 0.001) or with sound annoyance and distortion (both p 0.01) than in the groups with no symptoms. Hearing had been tested earlier for 96% of the conscripts, but of this group, 40% did not know the results of their hearing tests, 51% reported their hearing had been normal, and 4% reported permanent hearing loss. The most common reason for reporting hearing loss was exposure to loud music (60%), otitis media (8%), shooting firearms (4%), genetic reason (3%), and exposure to impulsive noise (2%). Type 1 hearing (normal) was found for 80% of the conscripts (n 841). However, 19% (n 202) had type 2, 3, or 4 hearing loss. When the group with actual hearing loss was compared with the self-reported hearing loss, 79% of the conscripts with hearing loss did not know or disclaimed their hearing loss, and only 18% knew their hearing was not normal. In the hearing loss group, the highest threshold shift was found at a frequency of 6,000 khz (25.1 db for the right ear and 29.9 db for the left ear on average). There was also a difference between the ears in the hearing loss group, the left ear having a 5 db lower average threshold than the right ear. No significant difference was found between the different frequencies and ears in the results of all of the conscripts. Discussion This study describes the hearing thresholds and leisure-time noise exposures of young men starting their military service in the Pori Brigade in Finland in January According to this study, 27% of the conscripts were exposed to weekly equivalent noise levels over 85 dba and 2% had already reached the lifetime limit for cumulative exposure. Our earlier studies with the same type of calculation method estimated that 50% of teenagers (12 16 years of age) and 9% of adults (25 55 years of age) are exposed to equivalent sound levels of 85 dba during the week. 9,11 Our results seem to fall between the teenagers and adults. There were some differences, TABLE II DISTRIBUTION OF SELF-REPORTED HEARING SYMPTOMS (N 1054) Symptom Never (%) Sometimes (%) Often (%) Continuously (%) Tinnitus related to noise Tinnitus for other reason Pain in ear Sound annoyance Sound distortion TTS

4 Cumulative Noise Exposure of Finnish Conscripts 115 TABLE III WEEKLY NOISE EXPOSURE (L EX,W ) AND LIFETIME NOISE EXPOSURE (L EX,TOT ) IN DIFFERENT HEARING SYMPTOMS GROUPS AND SIGNIFICANCE S OF DIFFERENCE a L EX,W Symptom Never Sometimes Often Continuously Never Sometimes Often Continuously Tinnitus related to noise Tinnitus for other reason Pain in ear NS NS Sound annoyance Sound distortion TTS a, p 0.5;, p 0.01; and, p 0.001; NS, not significant. L EX,tot however, in the activities reported by our conscripts and the teenagers and adults studied earlier, and these differences may have affected the results. The conscripts of this study more often attended nightclubs and pubs (two times more often), and they used home tools twice as much as teenagers and adults. However, their attendance at motor sports events was less frequent (50% less) than the teenagers. The differences in the hours used and participation in other activities between conscripts and the teenagers were however small. On a whole, the young adults were more active in several noisy activities and used more hours during the week in noisy activities than the adults did. This difference may explain the results in comparison to what is typical for an adult population. This study seemed to confirm the assumption that young men in their early 20s attend certain noisy activities, such as going to nightclubs during a certain period of their lifetime. 12 There seemed to be a connection between self-reported hearing symptoms, such as tinnitus and TTS, and personal noise exposure, those having symptoms statistically significantly more often also having high exposure levels. The conscripts with high personal lifetime noise exposures complained more often of hearing symptoms than the subjects with no symptoms did. Distortion and sound annoyance also seemed to be more common for the conscripts exposed to high noise levels. In this material, tinnitus in relation to noise exposure was experienced sometimes by 66.6% of the conscripts and often by 6.8%. TTS was reported sometimes by 45% and often by 1.6%. Jokitulppo et al. 9 reported tinnitus sometimes for 69.6% and often for 2.5% among teenagers (ages years) and TTS was experienced sometimes by 42.5% and often by 2.7%. The similar results have been reported by Smith et al. 13 for 66% of their subjects, who were 18- to 25-year olds attending nightclubs or rock concerts and who reported temporary effects on their hearing or tinnitus. The prevalence of permanent hearing loss ( 20 db HL) in this material was 19%. Axelsson et al. 14 found hearing loss in 15% of young Swedish males (n 500) and Sorri et al. 6 reported hearing loss for 18% of their subjects (n 536). The results of the present study seem to indicate a similar incidence, rather than an increase in recent years. However, Borchegrevink 7 reported high-frequency hearing loss of 20 db in 18% of his subjects in 1981, with an increase to 35.7% in In his study, it was suggested that the most probable cause of hearing loss was the increased exposure to loud music. 7 According to this study, the most common reason for self-reported hearing loss was exposure to loud music, but this result is the true cause of only 18% of hearing loss. Altogether 11% of hearing loss was related to otitis media, shooting firearms, genetic causes, or fireworks and 10% had a nonspecified reason. Altogether, for 61% of those diagnosed with hearing loss the cause was something other than a factor in the predicting list because most of these conscripts did not know they had hearing loss when they answered the questionnaire. The estimations of some leisure-time activities and the actual noise levels may have had an effect on the total weekly noise exposure levels to some extent. Equivalent noise levels may underestimate the actual noise exposure, because noise exposure includes both steady noise and impulse noise, such as shots from firearms and fireworks. In addition, in other activities, such as motor sports and movies, the noise levels vary during the performance, and the estimation of loudness may be based on relatively short periods of action. However, the results of this study provide one type of method for evaluating the total leisure-time noise in young adults. Conclusions According to this study, the prevalence of hearing loss is approximately 20% among young Finnish men before military service. One-third of the conscripts included in our study were exposed weekly to noise levels high enough to be a hearing risk. The high incidence of hearing symptoms with high exposure levels seems to confirm the assumption that leisure-time noise exposure is a significant factor in the development of hearing loss and hearing symptoms among the young. The cumulative effect of noise during military service opens a question about the progression of hearing loss during this period. In addition, more information on the equivalent sound levels of some leisure-time activities (e.g., listening to home stereo, watching movies) and more knowledge about the estimation of loudness levels of leisure-time activities is needed. References 1. EEC: Council Directive of May 12, 1986 on the Protection of Workers from the Risks Related to Exposure to Noise at Work. EEC Council Directive 86/88(EEC) Brussels, EEC, ACGIH: Threshold limit values for physical agents in the work environment: adapted by ACGIH Cincinnati, OH, ACGIH, Brown PJ, Yearout RD: Impacts of leisure noise levels on safety procedures and policy in the industrial environment. Int J Industrial Ergonomics 1990; 7: Clark WW: Noise exposure from leisure activities: a review. J Acoust Soc Am 1991; 90:

5 116 Cumulative Noise Exposure of Finnish Conscripts 5. Passchier-Vermeer W, Passchier W: Noise and public health. Environ Health Perspect 2000; 108: 1: Sorri M, Riihikangas P, Ojala K, Sipilä P: Audiometric findings at the beginning of military service. Ann Med Milit Fenn 1980; 55: Borchegrevink HM. One third of 18-year-old male conscripts show noise induced hearing loss 20 db before start of military service the incidence being doubled since 1981 reflecting increased leisure noise? In: Proceedings of the 5th International Congress on Noise as Public Health Problem, 1998, Vol 2, pp Edited by Berglund K, Karlsson J, Lindvall T. 8. Borchegrevink HM: Effects of noise and blasts. Scand Audiol 1990; 19(Suppl 34): Jokitulppo J, Björk E, Akaan-Penttilä E: Estimated leisure noise exposure and hearing symptoms in Finnish teenagers. Scand Audiol 1997; 26: International Organization for Standardization (ISO) (1990): 1999 Acoustics Determination of Occupational Noise Exposure and Estimation of Noise-Induced Hearing Impairment. Geneva, ISO, Jokitulppo J, Björk E: Estimated leisure-time noise exposure and hearing symptoms in Finnish urban adult population. Noise Health 2002; 5: Meyer-Bisch C: Epidemiological evaluation of hearing damage related to strongly amplified music (personal cassette players, discotheques, rock-concerts) high-definition audiometric survey on 1364 subjects. Audiology 1996; 35: Smith PA, Davis A, Ferguson M, Lutman M: The prevalence and type of social noise exposure in young adults in England. Noise and health 2000; 6: Axelsson A, Rosenhall U, Zachau G: Hearing in 18-year-old Swedish Males. Scand. Audiol 1994; 23: 2: