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|Year : 2013
: 15 | Issue : 67 | Page
|The prevalence of audiometric notches in adolescents in Germany: The Ohrkan-study
Dorothee Twardella1, Carmelo Perez-Alvarez2, Thomas Steffens2, Gabriele Bolte3, Hermann Fromme4, Ulla Verdugo-Raab1
1 Department of Occupational and Environmental Medicine and Epidemiology, Bavarian Health and Food Safety Authority, Munich, Germany
2 Department of Otorhinolaryngology, University Hospital Regensburg, Germany
3 Department of Occupational and Environmental Medicine and Epidemiology, Bavarian Health and Food Safety Authority, Munich; Department of Social Epidemiology, University of Bremen, Germany
4 Department of Chemical Safety and Toxicology, Bavarian Health and Food Safety Authority, Munich, Germany
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|Date of Web Publication||12-Nov-2013|
Although there is concern about increasing hearing loss in adolescents caused by leisure noise exposure, prevalence data are scarce. In an US study, about 16-17% of adolescents were affected by audiometric notches. To estimate the prevalence of audiometric notches in adolescents in Germany, baseline data of the cohort study Ohrkan, recruitment during the school years 2009/2010 and 2010/2011 were analyzed. All students in grade 9 visiting any school in the city of Regensburg were eligible for participation. Data was collected via standardized questionnaires from students and their parents. In addition, students were asked to visit the University Clinics of Regensburg for ear examination including a tympanogram and the determination of hearing thresholds in air conduction audiometry. The prevalence of audiometric notches was determined in students with normal tympanogram in both ears and complete audiometry data. Audiometric notches were defined according to criteria used to analyse US data. Overall, 2149 students (1158 girls, 991 boys mainly aged 15-16 years) of the 3846 eligible adolescents (56%) participated. Among the 1843 adolescents with complete audiometry and tympanometry data, the prevalence of audiometric notches was 2.4% (95% confidence interval 1.7-3.1%). We could not confirm the high prevalence of audiometric notches as reported in National Health and Nutrition Examination Surveys for adolescents in the US. Differences in prevalence might be at least partly due to methodical differences in audiometry. Even if empirical evidence is presently ambiguous, it is reasonable to educate young people about the potential risks of high leisure noise exposure.
Keywords: Adolescent, hearing loss, noise, socio-economic factors
|How to cite this article:|
Twardella D, Perez-Alvarez C, Steffens T, Bolte G, Fromme H, Verdugo-Raab U. The prevalence of audiometric notches in adolescents in Germany: The Ohrkan-study. Noise Health 2013;15:412-9
|How to cite this URL:|
Twardella D, Perez-Alvarez C, Steffens T, Bolte G, Fromme H, Verdugo-Raab U. The prevalence of audiometric notches in adolescents in Germany: The Ohrkan-study. Noise Health [serial online] 2013 [cited 2014 Sep 23];15:412-9. Available from: http://www.noiseandhealth.org/text.asp?2013/15/67/412/121241
| Introduction|| |
Cross-sectional studies from the 1980s on hearing conducted among male conscripts have produced alarming results: Prevalence of hearing loss as high as 36% among 18-year-old has been observed. , Since these young men had not been exposed to occupational noise yet, leisure time exposures such as listening to amplified music at rock concerts and discotheques and via earphones have been assumed to be responsible for the presumed increase in prevalence. Other research has shown that noise levels at concerts and in discotheques easily reach 100 dB , and that those who visit discotheques stay there for on average of about four hours per week h. ,, According to observations from occupational health, the exposure to these high noise levels at reported durations over a long period of time can cause noise-induced hearing loss.  Similarly, a review of the Scientific Committee on Emerging and Newly Identified Health Risks on health risks of personal music players (PMP) concluded that considering the daily time spent on listening to music through PMP and the typical volume control settings, approximately 5-10% of the listeners are at high risk of developing permanent hearing loss after 5 or more years of exposure. 
Good hearing is a prerequisite for the detection, identification and localization of sounds and for speech recognition, especially in difficult environments. Uncorrected hearing loss can reduce social activity and quality of life.  Because of the consequences for the affected individuals and the associated societal and the economic costs , an increase in the prevalence of hearing loss would be of major public health importance.
Still, only few prevalence data are available. ,, The most comprehensive prevalence data come from the US American National Health and Nutrition Examination Surveys (NHANES). ,, In the survey 1988-1994 (NHANES III, 2519 youth aged 12 to 19 years, 50.3% female), the prevalence of audiometric results suggestive of a noise-induced hearing loss (audiometric notches) was 15.9%. In the NHANES survey 2005-2006 (1791 youth of the same age group, 48.0% female), i.e., about 14 years later, the prevalence of audiometric notches did increase to 16.8%, but this increase was not statistically significant. Comparable up-to-date data from Europe are missing. In addition, since prevalence studies often were based on male conscripts or adolescents entering the industrial workforce, prevalence data among female adolescents are especially scarce.
To collect data on hearing thresholds in adolescents in Germany, on their exposure to leisure noise, and to assess associations prospectively, we initiated the cohort study Ohrkan (The name "Ohrkan" was made-up for the study from the German word for ear "Ohr" as well as the German word for thunderstorm "Orkan"). The current paper reports results of the baseline data collection and focuses on the prevalence of audiometric notches and low and high frequency hearing loss in adolescents and socio-demographic determinants.
| Methods|| |
For Ohrkan, a cohort of adolescents was recruited in the city of Regensburg, a small city in the state of Bavaria, Germany, with about 135,000 inhabitants. The background and design of Ohrkan has been described in detail elsewhere.  The basic features are given below. The study was approved by the Ethics Committee of the University of Regensburg. The baseline assessment of the cohort members took place between October 2009 and July 2011.
To achieve a high participation rate, adolescents were approached in schools. All students who visited any school in the city of Regensburg and were in grade 9 in the school year 2009/2010 or 2010/2011 were eligible for participation. Since according to the German school system all adolescents have to finish at least the 9 th grade, this sample can be regarded representative of the general population of adolescents. In Regensburg, considering all types of schools and private as well as public institutions, 27 schools covering grade 9 were identified. To calculate the number of eligible subjects, the number of boys and girls in each class of grade 9 was obtained. For the second school year, the number of boys and girls who repeated class was subtracted. This resulted in 3846 students (1970 girls and 1876 boys) who were eligible for study participation.
Among the 27 secondary schools in Regensburg, all except one remedial school with 11 eligible subjects (4 girls, 7 boys) cooperated in recruitment. Written material including information sheets and questionnaires were distributed in class. In addition, during one class hour study personnel gave an oral presentation on the study background and aimed to motivate students for participation. Informed consent was obtained from students as well as from their parents.
Students had to fill out a standardized questionnaire which comprised data on noise exposures and self-reported hearing ability and tinnitus. An additional standardized questionnaire was answered by parents, which included information on socio-demographic factors and medical history of the adolescent. Adolescents were asked to undergo an examination of the ears. Just before the examination the students had to fill out a short standardized documentation sheet which included information on noise exposure within the last 24 h and current diseases, which could affect hearing ability. To increase response rates participants received a gift certificate for a local cinema and a lottery of prizes with the overall value of 3,000 € was implemented.
Tympanometric compliance and audiometric measures
All examinations were conducted at the Department of Otorhinolaryngology at the University Hospital Regensburg by clinic staff using the usual standardized procedures. Compliance testing and audiometry were conducted in two sound-treated rooms with comparable equipment. For compliance testing, MADSEN Zodiac 901 Tympanometer was used in both rooms. Failure of tympanogram was defined as (a) a peak of the curve at pressure below- 100 daPa (decapascal) (low pressure) or (b) a peak of the curve at pressure above +100 daPa (excess pressure) or (c) no peak observable. Audiometry was performed either with clinical audiometer MADSEN-Aurical (GN Otometrics, Denmark) and Holmco PD95 headphone (Holmco Elektroakustik, Germany), calibrated according to DIN EN ISO 389-1:2000-09, or MADSEN Itera II (GN Otometrics, Denmark) with Sennheiser HDA200 headphone (Sennheiser Electronic, Germany), calibrated according to DIN EN ISO 389-1:2000-09. , Both head phones are designed for pure-tone air conduction and speech audiometry.
Holmco PD95 is a supra-aural headphone with a bandwidth of 50 up to 15 000 Hz, HDA 200 is a pair of closed (circum-aural) dynamic ear protector headphones with a bandwith of 20 to 20 000 Hz. Both audiometers are standard two-channel clinical audiometers and comply with DIN EN 60645-1.  This part of IEC 60645 specifies general requirements for audiometers and requirements specific to pure-tone audiometer, which are provided for determining the hearing threshold compared with the standard reference threshold level using psychoacoustic testing.
Air conduction thresholds were determined for each ear for the frequencies 1000 Hz, 2000 Hz, 3000 Hz, 4000 Hz, 6000 Hz, 8000 Hz, 500 Hz, 250 Hz, 125 Hz across intensity ranges of −10-110 dB using 5 dB step intervals.
The main outcome was the presence of a notched audiogram. To identify a notched audiogram we used the criteria that were applied by Niskar et al., to describe the so called "noise-induced threshold shift" in the analysis of the NHANES data. , An audiometric notch was considered to be present if in at least one ear
- threshold values at 0.5 and 1 kHz were ≥15 dB HL (better), and
- the maximum (poorer) threshold value at 3, 4, or 6 kHz was at least 15 dB HL higher (poorer) than the highest (poorest) threshold value for 0.5 and 1 kHz, and
- the threshold value at 8 kHz was at least 10 dB HL lower (better) than the maximum (poorest) threshold value for 3, 4, or 6 kHz.
As secondary outcomes, low frequency hearing loss (LFHL) and high frequency hearing loss (HFHL) were specified according to criteria from Henderson et al.  LFHL was present if in at least one ear the average threshold at 0.5, 1, and 3 kHz was >15 dB HL. HFHL was defined as an average threshold at 3, 4, and 6 kHz of >15 dB HL in at least one ear.
Only subjects who in both ears passed compliance testing and had complete data on pure tone air conduction audiometry were considered. Firstly, students were described with respect to their socio-demographic characteristics. If the adolescent was born in Germany, had German parents and German was the only language spoken at home, migration background was categorized "None". Else if both the mother and father were of German nationality, but the adolescent was born abroad and/or foreign languages were spoken at home, the category "possible" was chosen. In case of foreign nationality of father and/or mother migration background was categorized "yes".
Next, we described the distribution of hearing thresholds at each frequency and in each ear separately and determined the proportion of students meeting the criteria for LFHL, HFHL and audiometric notches. The association between LFHL, HFHL and audiometric notches and the socio-demographic background of the adolescents was evaluated using bivariate logistic regression. All statistical computations were implemented using SAS statistical software, release 9.2 (SAS Institute Inc., Cary, North Carolina).
| Results|| |
Overall, 2149 students (55.9%) agreed to participate in Ohrkan and 1933 took part in the examination of the ears. Of those, four subjects had to be excluded from the present analysis because audiometry data were incomplete, five had to be excluded because of incomplete compliance data, and 76 because they failed compliance testing. Further five students wore hearing aids at the examination and thus their data were not used in the analysis. As a result, analysis was based on data from 1843 students (47.9% of all eligible subjects). Most of the students were 15 to 16 years old, 55% were female [Table 1].
The majority of hearing thresholds at any frequency in both ears showed levels between 0 dB HL and 10 dB HL [Figure 1], [eTable 1] [Additional file 1] and [eTable 2] [Additional file 2]. Hearing thresholds of 15 dB HL or worse were observed in only 2-18% of participants' ears depending on frequency. Higher thresholds were more prevalent at frequencies 4 kHz, 6 kHz and 8 kHz and to a lesser degree also at frequencies of 125 Hz and 250 Hz.
An audiometric notch was observed in 44 subjects (2.4%, 95% confidence interval (CI) 1.7-3.1%) [Table 2]. High frequency hearing loss was more prevalent (3.6%, 95% CI 2.8-4.5%) than LFHL (1.5%, 95% CI 0.9-2.0%). Bilateral hearing loss was observed in 14% (audiometric notches), 44% (LFHL), and 30% (HFHL) of the cases respectively. In case of LFHL (left ear 20, right ear 19) and HFHL (left ear 45, right ear 42) both ears were equally often affected while in case of audiometric notches more subjects were affected in the left ear (30) than in the right ear (20).
|Table 2: Prevalence of audiometric notches, LFHL, and HFHL in relation to the sociodemographic background of adolescents|
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The prevalence of hearing loss differed by socio-demographic background of the adolescents [Table 2]. Audiometric notches as well as LFHL and HFHL were more prevalent in school types of lower educational status. In addition, audiometric notches occurred more often in students with (possible) migration background and consistent with that, in students born abroad. The prevalence of audiometric notches was little higher in males than females. There was no increase in audiometric notches by age.
LFHL occurred more often in adolescents with parents of medium school education than in adolescents with parents of high school education (Odds ratio (OR) = 2.78; 95% CI 1.18-6.56). Adolescents with parents of low school education showed prevalence similar to those from high education parents. HFHL occurred more often in students from private than from public schools, and there also appeared to be some increase with age.
With respect to HFHL no significant association with socioeconomic factors could be observed. However, there was a trend of increased prevalence in students from lower school types.
| Discussion|| |
Ohrkan is the only recent study on the prevalence of hearing deficits in adolescents from Europe. We were able to analyse air conduction hearing thresholds from 1843 students in grade 9 (mostly 15 to 16 years old). Hearing losses were seldom observed; the prevalence of audiometric notches, HFHL, and LFHL, respectively, was only a few percent. The prevalence of audiometric notches was associated with school type and migration background but not significantly associated with age or sex.
Only few studies did provide data on the prevalence of hearing loss in adolescents in the past. [Table 3] shows prevalence estimates from studies on adolescents conducted in Germany, published in scientific journals as well as in reports, and in addition journal articles since the year 2000 from other European countries. Studies are heterogeneous in particular with respect to the study population and criteria used to define hearing loss. To facilitate comparison, prevalence estimates using the data of the Ohrkan study were calculated by applying the criteria of the respective study. The comparison reveals, that apart from the study by Barrenäs et al.,  in all studies a higher prevalence of hearing loss is reported as would be estimated if the same criteria were applied in Ohrkan.
|Table 3: Prevalence estimates of hearing loss in adolescents from studies conducted in Germany and European studies published since the year 2000|
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This is also true for the NHANES study. Although in Ohrkan as well as in NHANES only subjects who passed tympanometry were used in analyses and the same criteria for audiometric notches were applied, the prevalence in Ohrkan (2.4% in mostly 15-16 year old adolescents) was much lower than in the NHANES survey 1988-1994 (15.9% in youth aged 12 to 19 years) and in the NHANES survey 2005-2006 (16.8% in youth of the same age group). , Green argued that the high prevalence of audiometric notches in NHANES would be an artefact caused by systematic measurement errors as well as statistical variability.  In particular, a higher variability at 6 kHz or a systematic calibration error related to specific types of headphones were given as possible reasons for a mean threshold at 6 kHz, which was higher than the mean thresholds at other frequencies.  This poorer thresholds at 6 kHz increase the likelihood of false positive diagnosis of audiometric notches, as shown in simulations. In Ohrkan, a different type of headphone (Holmo PD95 and Sennheiser HDA200) was used than in NHANES (supra-aural earphone TDH-50). Mean threshold at 6 kHz was not increased in Ohrkan. A reduced number of false-positive diagnoses in Ohrkan could thus be one possible explanation for a reduced prevalence of audiometric notches in Ohrkan compared to NHANES.
Differences in audiometric notches prevalence may at least be partly due to differences in leisure noise exposure of adolescents in the US compared to Germany. For example, in NHANES 2005-2006 42% of male and 15% of female adolescents have ever used firearms.  In Ohrkan, less than 6% of the adolescents report that they shoot with firearms. In addition, in Ohrkan only 9% of the participants are aged 17-19 years. In NHANES, 23% of participants are of age 18-19 and probably an additional 13% of age 17. If we assume that noise exposure results in hearing loss only after some years, this difference in age distribution might at least partly be responsible for the difference in the prevalence of audiometric notches.
The low prevalence in Ohrkan could also be due to selective participation. About 50% of the adolescents participated in Ohrkan. This response rate is high in comparison to other surveys among adolescents,  but still leaves much possibility for selection bias. Since the topic of the study was on hearing, the probability that those adolescents who have already problems with hearing decline to participate is larger than in studies such as NHANES, in which hearing is just one of a multitude of topics. As can be seen from [Table 1], participation differed by sex, school type and ownership, respectively. The increased participation of students from Gymnasium and Hauptschule, however, does, if at all, indicate rather an overestimation than an underestimation of audiometric notches prevalence in Ohrkan.
Finally, audiometry methods differed. The Ohrkan study was implemented in a clinical setting and the professional clinic staff with a 3 year education in audiology used regularly calibrated clinic-owned equipment for the examinations. In NHANES as in other field studies examinations were conducted in a mobile examination booth by particularly trained staff. Control of background noise may be less efficient in a mobile examination booth. Experienced staff may make fewer mistakes. In Ohrkan, the examinee and the study assistant conducting the examination were sitting in the same room. A visual barrier was used to prevent the examinee from observing the keyboard of the study assistant and thus knowing when the assistant stroke a key to switch-on a tone in audiometry. However, this barrier was small and may not have been sufficient. To prevent errors by visually information when a tone is switched-on, sham stimulations were included by simulating the movement of the hand without switching-on a tone.
Recent data on the prevalence of hearing loss in female youth are particularly scarce since many studies either are based on males only. ,,, Data from NHANES III (1988-1994) and from the German Environmental Survey on Children 2003-2006 suggest that the prevalence of audiometric notches is higher in male than in female adolescents. , However, in the more recent NHANES survey from 2005 to 2006 the prevalence estimates of males and females have equalled and differences are no longer statistically significant.  Similarly, we found only a non-significant difference in prevalence among males and females. In NHANES 2005-2006 it was argued that the increase in audiometric notches in females was caused by a catch-up in noise exposure. However, data of the same study do not suggest this causal effect: the noise exposure was still higher in males than in females, and noise exposure was not associated with audiometric notches. 
In our study data, there are no indications that a high proportion of young adolescents is already affected by hearing loss caused by leisure noise exposure as was suggested based on NHANES or other studies. Possible reasons for differences in prevalence estimators have been discussed above. Besides, when looking at the results of our study as well as results of other cross-sectional surveys including NHANES, the interpretation of a notched audiogram as a noise-induced threshold shift is worth discussing. While long term noise exposure typically causes a notched audiogram, a notched audiogram alone may not be sufficient evidence for a noise-induced hearing loss. Green argues that the definition of a noise-induced threshold shift entails a difference in hearing levels between baseline and follow-up audiograms as well as concurrent noise exposure.  To overcome this limitation repeated examinations of the Ohrkan cohort are planned in the future so that a comparison of audiograms from different time points as well as analysis of concurrent noise exposure will be possible.
| Conclusion|| |
In our cohort of 1843 adolescents we could not confirm the high prevalence of audiometric notches that was reported by former studies. Differences in methods of audiometry may have contributed to the difference in prevalence. Also, lower leisure noise exposure as well as differences in age distribution might explain the low prevalence in Ohrkan. Selection effects in the Ohrkan study cannot be excluded. Since the effects of leisure noise exposure might manifest not until several years, we plan to follow the study participants prospectively. Even if empirical evidence is presently ambiguous, it is highly plausible, that leisure noise as much as industrial noise has the potential to cause a risk for hearing. Thus, information and education about this potential risk particularly among young people is warranted.
| Acknowledgment|| |
This study was funded by the Bavarian Ministry for the Environment and Health. We wish to thank the participating schools, the teachers and students for their support of the study as well as Carmen Moritz for her never fading commitment in the recruitment of study participants, the staff of the University Hospital Regensburg (Christine Fleischmann, Gerlinde Kammerl, Susan Kerta, Katrin Rau, Jessica Rögner, Heike Schmidt, and Stefanie Schnabel) for the reliable organisation and conduction of the auditometry, Martina Hoffmann, Annette Mangstl, and Simone Zyzik-Zinn for support in data management, Angelika Zirngibl for data management and Petra Böhm and Angelika Schwaiger for assistance in organisational matters.
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Department of Occupational and Environmental Medicine and Epidemiology, Bavarian Health and Food Safety Authority, Pfarrstrasse 3, 80538 Munich
[Table 1], [Table 2], [Table 3]