Unilateral hearing impairment in Oman: a community-based cross-sectional study.Abstract
This report on unilateral hearing loss Unilateral hearing loss (UHL) or single-sided deafness (SSD) is a type of hearing impairment where there is normal hearing in one ear and impaired hearing in the other ear. is based on the findings of a national survey on hearing loss and blindness in Oman. The survey of randomly selected households was conducted by trained healthcare personnel between Oct. 1, 1996, and Feb. 28, 1997. A total of 11,402 subjects of all ages were screened for hearing loss. Those who reported hearing impairment hearing impairment
A reduction or defect in the ability to perceive sound. in either ear were subsequently reexamined by otologists in hospitals to confirm the findings and to determine the cause of the hearing loss. Based on these findings, we calculated that the prevalence of unilateral hearing impairment throughout Oman was 30.06 per 1,000 population (95% confidence interval confidence interval,
n a statistical device used to determine the range within which an acceptable datum would fall. Confidence intervals are usually expressed in percentages, typically 95% or 99%. [CI]: 29.80 to 30.31). Males had a significantly higher rate (36.67/1,000 [95% CI: 34.55 to 38. 79]) than females (23.88/1,000 [95% CI: 21.82 to 25.94]). The causes of unilateral hearing loss were different from the reported causes of bilateral hearing loss. Impacted earwax earwax /ear·wax/ (er´waks) cerumen.
A waxlike secretion of certain glands lining the canal of the external ear; cerumen.
see cerumen. (16.0% of cases) and otitis media with effusion otitis media with effusion Secretory otitis media, see there (13.1%) were the most common identifiable causes of unilateral hearing loss; genetic causes were responsible for less than 2% of cases. Just over one-half of the hearing-impaired patients had only a mild hearing loss. Impairment rates varied in different regions of the country.
The global thrust for the management and prevention of hearing loss focuses mainly on bilateral impairment] but unilateral hearing loss is also important. Most affected patients either do not notice a loss of hearing when it occurs in only one ear or they are not bothered by it. Therefore, they are unlikely to seek intervention unless the hearing loss reaches an advanced stage.
The causes of unilateral hearing loss are largely different from those of bilateral hearing loss. (2) Evaluation of unilateral hearing impairment is critical to planning early intervention ear·ly intervention
n. Abbr. EI
A process of assessment and therapy provided to children, especially those younger than age 6, to facilitate normal cognitive and emotional development and to prevent developmental disability or delay. strategies that may prevent patients from becoming disabled--because of either disease progression or the development of comorbidity in the healthy ear.
Researchers in Oman conducted a survey on hearing loss (3) and blindness (4) during the mid-1990s. In this article, we present some of the findings of that survey. Our intention is to highlight the prevalence and causes of unilateral hearing impairment in the hope that this will enhance efforts to reduce this disability. This article complements our report on bilateral deafness, which was published in 2004. (3)
Patients and methods
We patterned the design of this community-based, cross-sectional study cross-sectional study
See synchronic study.
n the scientific method for the analysis of data gathered from two or more samples at one point in time. on a survey protocol recommended by the World Health Organization, (5) modifying it according to according to
1. As stated or indicated by; on the authority of: according to historians.
2. In keeping with: according to instructions.
3. disease trends particular to Oman. The survey was conducted into two phases: the screening phase (phase I) and the diagnosis and management phase (phase II).
The present study was part of a larger study of the prevalence of hearing loss (3) and blindness (4) in Oman. The sample size was calculated on the basis of a bilateral blindness rate of 1.5%. This resulted in a large sample for the hearing loss portion of the study, but this was unavoidable. For statistical analysis, the population of Oman was estimated at 1.65 million (mid-1996 projection). (6) Initially, we randomly selected 9,744 persons of all ages and both sexes for enrollment. At this size, the sample would achieve a 95% confidence interval (CI) with 90% power and a 15% error margin. However, to compensate for the "cluster effect The cluster effect is the effect of buyers and sellers of a particular good or service congregating in a certain place and hence inducing other buyers and sellers to relocate there as well. " and the expected loss of 15% of the sample, we enlarged the study population to 12,437. A three-stage, stratified stratified /strat·i·fied/ (strat´i-fid) formed or arranged in layers.
Arranged in the form of layers or strata. , and randomly selected cluster-sample method was used. The population was divided into clusters, and from this sampling frame, 116 clusters were selected at random.
Oman is made up of 10 health regions (figure). Within each region, clusters were stratified on the basis of population. Each cluster was made up of 12 neighboring neigh·bor
1. One who lives near or next to another.
2. A person, place, or thing adjacent to or located near another.
3. A fellow human.
4. Used as a form of familiar address.
v. houses. The selection of the first house in a cluster was made in a uniform manner. Then we selected the direction in which we would travel to visit other houses in a random fashion. All available family members were included in each household survey.
Thirty-four phase I teams carried out the household visits. Each of these teams included a physician and a nurse who routinely screen schoolchildren schoolchildren school npl → écoliers mpl;
(at secondary school) → collégiens mpl; lycéens mpl
schoolchildren school for hearing status.
The phase II teams were made up of selected specialists and nurses from hospital ENT ENT ears, nose, and throat (otorhinolaryngology).
ear, nose, and throat
ear, nose and throat.
ENT Ears, nose & throat; formally, otorhinolaryngology departments. A central committee headed by the authors coordinated all survey activities. Permission to conduct surveys was obtained from village elders or tribal chiefs. To promote citizen participation and cooperation, the dates and purpose of the survey were publicized pub·li·cize
tr.v. pub·li·cized, pub·li·ciz·ing, pub·li·ciz·es
To give publicity to.
Adj. 1. publicized - made known; especially made widely known
publicised in the national news media.
Survey teams recorded personal data (name, age, sex, etc.) and clinical information (hearing status and the results of an otoscopic ear examination) for each participant on a household register. All subjects aged 4 years and older were screened with a portable audiometer au·di·om·e·ter
An electrical instrument for measuring the threshold of hearing for pure tones of normally audible frequencies generally varying from 200 to 8000 hertz and recorded in decibels. ; sound stimuli at 1, 2, and 4 kHz and 25 and 35 dB were applied to each ear in random order. Data on the hearing status of children 3 years and younger were collected by subjective methods.
All subjects with definite or possible hearing loss or ear disease were referred to a phase II specialist for confirmation of findings or refutation ref·u·ta·tion also re·fut·al
1. The act of refuting.
2. Something, such as an argument, that refutes someone or something.
Noun 1. of suspicion. Any subject who failed to hear pure tones at 25 dB in the range of 2 to 4 kHz and at 35 dB at 1 kHz was tested a second time; if he or she still failed to hear the stimulus, hearing impairment was suspected and the subject was referred for a phase II investigation.
In accordance with the WHO guidelines, (5) a subject was considered to have unilateral hearing impairment when an unaided un·aid·ed
Carried out or functioning without aid or assistance: made an unaided attempt to climb the sheer cliff. heating threshold of 26 dB or greater was found in either ear. The threshold of the better-hearing ear was used to establish the degree of hearing loss in the worse-hearing ear. Hearing loss was classified as mild (hearing threshold: 26 to 40 dB), moderate (41 to 60 dB), severe (61 to 80 dB), or profound ([greater than or equal to] 81 dB).
Prior to the actual survey, the central committee conducted a pilot survey in a wilayat (district) outside the survey area to test the methodology and maintain high standards. Afterward, all survey teams participated in a workshop in which standard methodology, definitions, parameters, and possible difficulties were discussed and agreed upon Adj. 1. agreed upon - constituted or contracted by stipulation or agreement; "stipulatory obligations"
noncontroversial, uncontroversial - not likely to arouse controversy . To test the quality of the phase I component of the survey, we compared the findings of the phase I teams with that of otologists and estimated the agreement rates. Depending on the outcomes of this quality assessment, the otologists recommended steps to improve screening. The survey protocol was written in a manual so that it could be used as a reference by the field staff.
The data were audited in the field and forwarded to a data manager. Data were compiled on EPI EPI
exocrine pancreatic insufficiency. 6 software, and precautions were taken to reduce errors. Univariate analysis was carried out using the Statistical Package for the Social Studies (SPSS A statistical package from SPSS, Inc., Chicago (www.spss.com) that runs on PCs, most mainframes and minis and is used extensively in marketing research. It provides over 50 statistical processes, including regression analysis, correlation and analysis of variance. ), version 9. The frequencies, crude rates, estimated number of persons with hearing impairment in the entire population, and age- and sex-adjusted prevalence rates were calculated. For statistical validation, 95% CIs were calculated.
Confidentiality of individual subjects' health information was maintained. Group findings were used to promote the improvement of ear care services in Oman, and this information was disseminated among the various regions via national seminars.
A comparison of the study population with the overall Omani population by sex and age group is shown in table 1. The male-to-female ratio among the overall population at the time of the study was 1.03:1, whereas the ratio in the study population was 0.9:1. Also, our study population included disproportionately fewer subjects from the working class (primarily younger men who were away at work) and disproportionately more children (even so, note that Oman has a large population of young people). Therefore, we took the sex and age differences into consideration and adjusted our findings accordingly.
Of the 12,437 subjects chosen for the study, 11,402 (91.7%) were actually surveyed. Of the remainder, 128 (1.0%) refused to participate and 907 (7.3%) were not present when the survey teams visited their homes. Hearing status could not be determined in 11 subjects. Regional variation in the amount of participation was minimal, ranging from 88.0 to 94.9%.
A total of 1,548 subjects were referred for phase II investigation of possible hearing loss or ear disease, and 1,478 (95.5%) actually underwent the follow-up examination. Of the 70 subjects who did not participate in phase II, 4 were suspected of having unilateral hearing loss; the rest had a common ear disease that did not affect their hearing in one ear.
Phase II investigation identified unilateral hearing impairment in 306 subjects (2.7% of the 11,402 subjects who were surveyed) (table 2). Impairment was mild in 166 subjects (54.2%), moderate in 90 (29.4%), severe in 31 (10.1%), and profound in 19 (6.2%). After further statistical analysis, we estimated that the adjusted prevalence of unilateral hearing impairment throughout Oman was 30.06 per 1,000 population (95% CI: 29.80 to 30.31). Males had a significantly higher rate than did females--36.67 and 23.88 per 1,000 population, respectively. As would be expected, hearing loss rates were highest in the oldest age group (65.66/1,000 adjusted); the rates decreased progressively and were lowest in the youngest group (8.53/1,000).
The lowest rate of unilateral hearing impairment was found in the Dhahira region (8.32/1,000), and the highest was in the South Sharqiya region (74.11/1,000) (figure). No cluster in the Wousta region was selected during randomization randomization (ranˈ·d·m , and therefore no rate is available.
The cause of unilateral hearing impairment was identified in only 180 of the 306 cases (58.8%) (table 3). The most common cause was impacted earwax (16.0%), and the second most common cause was otitis media with effusion (13.1%). A genetic cause was found in less than 2% of subjects. In 75 patients (24.5%), the cause was undetermined--that is, a detailed examination was not possible for various reasons. In 51 patients (16.7%), the cause was unknown--that is, the physician could not discern the cause after a proper examination.
Of the 166 cases of mild impairment, 86 (51.8%) were successfully resolved at the survey visit by simply clearing the ear canal ear canal
The narrow, tubelike passage through which sound enters the ear. Also called external auditory canal. of wax.
The participation rate in our study was 91.7%, so we clearly achieved our goal of high participation among eligible persons. The study sample's representation of the entire Omani population was not ideal, but it was acceptable. The primary problem in this regard was that many young men were away at work when the survey teams visited their homes. We attempted to compensate for this limitation by using age- and sex-standardized estimates.
The regional variation in the high and low rates of unilateral hearing loss was significant. One possible explanation might be climatic differences. The region with the lowest rate, Dhahira (8.32/1,000), is a landlocked landlocked adj. referring to a parcel of real property which has no access or egress (entry or exit) to a public street and cannot be reached except by crossing another's property. area with a hot and dry climate. The region with the highest rate, South Sharqiya (74.11/1,000), lies on the coast, and its climate is hot and humid.
Study limitations. Two limitations of our study might have skewed skewed
curve of a usually unimodal distribution with one tail drawn out more than the other and the median will lie above or below the mean.
skewed Epidemiology adjective Referring to an asymmetrical distribution of a population or of data the results somewhat:
* The hearing and otic profiles obtained by otologists from the 4 subjects with suspected unilateral hearing loss who did not participate in phase II screening were not available to us for analysis, and these 4 subjects were considered to be lost to follow-up. If all 4 actually did have unilateral hearing impairment, our reported prevalence would be underestimated by 1 per 1,000.
* The fact that data on children aged 3 years and younger were collected by subjective methods might have introduced a differential measurement bias into the study. Because subjective methods are less sensitive than audiometric au·di·om·e·ter
An instrument for measuring hearing activity for pure tones of normally audible frequencies. Also called sonometer.
au evaluation, the rate of unilateral hearing impairment among the youngest children might have been underestimated.
Comparisons with previous studies of children. Few studies have been conducted to determine the prevalence of unilateral hearing loss anywhere in the world. Of those that have been performed, most involved only children. Therefore, it is difficult to compare the results of previous studies with ours, which involved a population of all ages. However, we did attempt to compare our findings in the pediatric pediatric /pe·di·at·ric/ (pe?de-at´rik) pertaining to the health of children.
Of or relating to pediatrics. age groups with those of others. The prevalence of unilateral hearing loss in our study among children aged 10 through 19 years was 23.83 per 1,000. In the United States United States, officially United States of America, republic (2005 est. pop. 295,734,000), 3,539,227 sq mi (9,166,598 sq km), North America. The United States is the world's third largest country in population and the fourth largest country in area. , Lee et al reported that the prevalence among children aged 6 through 19 years in five racial subgroups ranged from 6.4 to 12.3 per 1,000.7 The higher rate in Oman is indicative of the limited amount of ear care services that were available in the past.
Our study found that males (of all ages) had a significantly higher prevalence of unilateral hearing impairment than did females. Vartiainen and Karjalainen (8) observed a similar sex variation among children in Finland, but Lee et al (7) found no sex difference among Hispanic children in the United States.
Etiology. Perhaps as many as one-third of the cases of unilateral hearing impairment in our study were the result of infection-related causes. A possible genetic etiology was implicated im·pli·cate
tr.v. im·pli·cat·ed, im·pli·cat·ing, im·pli·cates
1. To involve or connect intimately or incriminatingly: evidence that implicates others in the plot.
2. in fewer than 2% of cases. In their study, Vartiainen and Karjalainen reported a genetic cause in 2% of cases. (8) By contrast, Kiese-Himmel and Kruse reported a genetic cause in 12.6% of patients. (9) In view of the fact that Oman has a 38% consanguinity consanguinity (kŏn'săng-gwĭn`ĭtē), state of being related by blood or descended from a common ancestor. This article focuses on legal usage of the term as it relates to the laws of marriage, descent, and inheritance; for its rate (10) and a high rate of genetic blood disorders blood disorders,
n.pl hematologic dyscrasias that affect the component cells and plasma elements of the blood. They are generally divided into two broad groups: those in which an increase in bulk occurs (e.g. , (11) the low rate of genetic causes in our study should be investigated further to determine whether it is, in fact, that low. Moreover, it is possible that a genetic etiology might have been responsible for the hearing loss in those patients who had an inner ear condition and in those whose cause was undetermined or unknown.
Since 1994, as many as 90% of pregnant women in Oman have received prenatal care prenatal care,
n the health care provided the mother and fetus before childbirth. , and 95% have been immunized against rubella rubella or German measles, acute infectious disease of children and young adults. It is caused by a filterable virus that is spread by droplet spray from the respiratory tract of an infected individual. . (12) Therefore, the likelihood that a congenital hearing impairment was caused by a maternal infection is low.
We observed some interesting findings in comparing the causality causality, in philosophy, the relationship between cause and effect. A distinction is often made between a cause that produces something new (e.g., a moth from a caterpillar) and one that produces a change in an existing substance (e.g. of unilateral hearing impairment in the present study and bilateral hearing impairment in our previous study. (3) As mentioned, infective infective /in·fec·tive/ (in-fek´tiv)
1. capable of producing infection.
2. infectious (1).
Capable of producing infection; infectious. causes were responsible for perhaps as many as one-third of unilateral hearing losses but less than 20% of bilateral hearing losses. Aging-related conditions appear to be associated equally with unilateral and bilateral hearing loss, as does the presence of earwax. The cause was not determined in 24.5% and 29.2% of cases, respectively.
Children with unilateral hearing loss have been reported to have significant deficits in auditory and psycholinguistic psy·cho·lin·guis·tics
n. (used with a sing. verb)
The study of the influence of psychological factors on the development, use, and interpretation of language. skills, resulting in poor school performance. (13) Adults with unilateral impairment generally experience difficulty understanding conversations. All patients with unilateral hearing impairment are at risk of potential disability if the healthy ear subsequently becomes affected. Therefore, regardless of a patient's age, unilateral hearing impairment demands attention.
We hope that the findings of our study will enhance the continued improvement of ear health in Oman and reduce the prevalence of hearing loss. A national hearing-loss--control program should stress strategies for early detection and treatment.
(1.) Future Programme Developments for Prevention of Deafness and Hearing Impairment. Report of the Third Informal Consultation. WHO/PBD/PDH/00.9. Geneva Geneva, canton and city, Switzerland
Geneva (jənē`və), Fr. Genève, canton (1990 pop. 373,019), 109 sq mi (282 sq km), SW Switzerland, surrounding the southwest tip of the Lake of Geneva. : World Health Organization; Feb. 11-12, 1999.
(2.) Watier-Launey C, Soin C, Manceau A, Ployet MJ. [Necessity of auditory and academic supervision in patients with unilateral hearing disorder hearing disorder Audiology Any disruption in the normal hearing process, where sound waves are not converted to electrical signals or nerve impulses are not transmitted to the brain for interpretation . Retrospective study retrospective study,
a study in which a search is made for a relationship between one phenomenon or condition and another that occurred in the past (e.g. of 175 children]. Ann Otolaryngol Chit Cervicofac 1998;115:149-55.
(3.) Al Khabori M, Khandekar R. The prevalence and causes of hearing impairment in Oman: A community-based cross-sectional study. Int J Audiol 2004;43:486-92.
(4.) Khandekar R, Mohammed A J, Negrel AD, Al Riyami AA. The prevalence and causes of blindness in the Sultanate of Oman: The Oman Eye Study (OES). Br J Ophthalmol 2002;86:957-62.
(5.) WHO Ear and Hearing Disorders hearing disorders,
n.pl a structural or functional impairment of the ability to detect and recognize sound.
hearing disorders, indications of,
n. Survey. Protocol for a Population-Based Survey of Prevalence and Causes of Deafness and Hearing Impairment and Other Ear Diseases. Geneva: World Health Organization; 1999.
(6.) Annual Health Report 1996. Muscat, Oman Muscat (Arabic: مسقط Masqaṭ, IPA: [mʌsqʌtˁ]) is the capital and largest city in the Sultanate of Oman. : Ministry of Health, Sultanate of Oman; 1997:1-8.
(7.) Lee DJ, Gomez-Marin O, Lee HM. Prevalence of unilateral hearing loss in children: The National Health and Nutrition Examination Survey II and the Hispanic Health and Nutrition Examination Survey. Ear Hear 1998; 19:329-32.
(8.) Vartiainen E, Karjalainen S. Prevalence and etiology of unilateral sensorineural hearing impairment sensorineural hearing impairment
Hearing impairment caused by dysfunction of the neural elements involved in the conduction or interpretation of nerve impulses originating in the cochlea. in a Finnish childhood population. Int J Pediatr Otorhinolaryngol 1998;43:253-9.
(9.) Kiese-Himmel C, Kruse E. [Unilateral hearing loss in childhood. An empirical analysis comparing bilateral hearing loss]. Laryngorhinootologie 2001;80:18-22.
(10.) Rajab A, Patton MA. A study of consanguinity in the Sultanate of Oman. Ann Hum Biol 2000;27:321-6.
(11.) Sulaiman AJ, A1-Riyami A, Farid S Farid (فريد),also spelt Fahrid is an Arabic masculine personal name, meaning unique. Farid is a common male name in the Middle East, South East Asia, and other places with large muslim populations.
Farid is also Arabic name for red ruby. , Ebrahim GJ. Oman Family Health Survey 1995. J Trop Pediatr 2001;47(suppl 1): 1-33.
(12.) The World Health Report 2000--Health Systems: Improving Performance. Available at http://www.who.int/whr/2000/en/(access verified Jan. 16, 2007).
(13.) Brookhouser PE, Worthington DW, Kelly WJ. Unilateral hearing loss in children. Laryngoscope la·ryn·go·scope
A tubular endoscope that is inserted through the mouth and into the larynx and that is used for examining the interior of the larynx.
la·ryn 1991; 101:1264-72.
Mazin Al Khabori, FRCS FRCS Fellow of the Royal College of Surgeons.
Fellow of the Royal College of Surgeons (ENT); Rajiv Khandekar, Dip (Epi), MS (Ophth)
From the Department of Otolaryngology--Head and Neck Surgery and Communication Disorders communication disorder
Any of various disorders, such as stuttering or perseveration, characterized by impaired written or verbal expression. , Al Nahdha Hospital (Dr. Al Khabori), and the Eye and Ear Health Care Program (Dr. Khandekar), Ministry of Health, Muscat Muscat, Maskat, or Masqat (all: mŭs`kăt, mŭs`kət), city (1993 pop. 533,774), capital of Oman, SE Arabia, on the Gulf of Oman. It is flanked by rugged mountains. , Sultanate of Oman.
Reprint reprint An individually bound copy of an article in a journal or science communication requests: Dr. Rajiv Khandekar, Ophthalmologist ophthalmologist /oph·thal·mol·o·gist/ (of?thal-mol´ah-jist) a physician who specializes in ophthalmology.
A physician who specializes in ophthalmology. and Epidemiologist, EHCP, DGHA, MOH See modem on hold. (HQ) POB PoB - Prisoner of Bill : 393, Pin: 113, Muscat, Oman. Phone: 968-607-524; fax: 968-2460-1832; e-mail: rajshpp@ omantel.net.om
Table 1. Comparison of the study population with the overall Omani population by sex and age group Male population Age group Overall (A) Study (B) Difference (yr) (%) (%) (A - B) / A [less than or equal to] 9 32.5 37.2 -0.145 10 to 19 29.6 35.4 -0.196 20 to 29 14.9 8.6 0.423 30 to 39 8.1 5.2 0.358 40 to 49 5.6 5.0 0.107 50 to 59 4.7 3.6 0.234 [greater than or equal to] 60 4.6 5.0 -0.087 Female population Age group Overall (A) Study (B) Difference (yr) (%) (%) (A - B) / A [less than or equal to] 9 32.2 31.6 0.019 10 to 19 29.5 33.0 -0.119 20 to 29 14.3 13.3 0.070 30 to 39 8.8 8.9 -0.011 40 to 49 6.3 5.9 0.063 50 to 59 4.5 3.2 0.289 [greater than or equal to] 60 4.4 4.1 0.068 Table 2. Breakdown of cases of unilateral hearing loss (UHL; n = 306) by sex and age group Number of UHL cases per 1,000 Estimated number UHL cases in the study of UHL cases in the Variable n (%) population overall population Sex Male 158 (51.6) 29.27 30,173 Female 148 (48.4) 24.65 21,019 Age group (yr) [less than or equal to] 9 36 (11.8) 5.81 4,508 10 to 19 95 (31.0) 40.60 12,140 20 to 29 47 (15.4) 51.31 12,108 30 to 39 36 (11.8) 48.26 6,631 40 to 49 35 (11.4) 64.22 5,426 50 to 59 27 (8.8) 72.19 4,128 [greater than or equal to] 60 30 (9.8) 103.09 6,251 Total 306 26.84 51,192 Adjusted number of UHL cases per 1,000 Variable in the overall population 95% CI Sex Male 36.67 34.55 to 38.79 Female 23.88 21.82 to 25.94 Age group (yr) [less than or equal to] 9 8.53 8.28 to 8.78 10 to 19 23.83 23.42 to 24.25 20 to 29 45.22 44.43 to 46.00 30 to 39 47.71 46.59 to 48.83 40 to 49 54.28 52.87 to 55.68 50 to 59 64.97 63.06 to 66.89 [greater than or equal to] 60 65.66 64.09 to 67.23 Total 30.06 29.80 to 30.31 Table 3. Causes of unilateral hearing loss by sex Cause Male Female Total (%) n (%) n (%) Impacted earwax 25 (15.8) 24 (16.2) 49 (16.0) Otitis media with effusion 18 (11.4) 22 (14.9) 40 (13.1) Chronic suppurative otitis media 13 (8.2) 14 (9.5) 27 (8.8) Noninfectious etiology 16 (10.1) 11 (7.4) 27 (8.8) Dry perforation 8 (5.1) 16 (10.8) 24 (7.8) Inner ear condition 4 (2.5) 5 (3.4) 9 (2.9) Genetic cause 3 (1.9) 1 (0.7) 4 (1.3) Undetermined * 42 (26.6) 33 (22.3) 75 (24.5) Unknown * 29 (18.4) 22 (14.9) 51 (16.7) Total 158 148 306 * "Undetermined" indicates that a detailed ear examination was not performed for various reasons; unknown indicates that a cause could not be identified after a proper examination.