The epidemiology of hearing impairment in an Australian adult population

Transcription

1 International Epidemiological Association 1999 Printed in Great Britain International Journal of Epidemiology 1999;28: The epidemiology of hearing impairment in an Australian adult population DH Wilson, a PG Walsh, b L Sanchez, c AC Davis, d AW Taylor, a G Tucker e and I Meagher a Background This study measured the prevalence of hearing impairment, and major demographic factors that influence the prevalence, in a representative South Australian adult population sample aged 15 years. Methods The study group was recruited from representative population surveys of South Australians. Participants in these surveys who reported a hearing disability were then recruited to an audiological study which measured air and bone conduction thresholds. In addition a sample of those people who reported no hearing disability were recruited to the audiological study. Results The data reported in this study are the first in Australia to assess the prevalence of hearing impairment from a representative population survey using audiological methods. The data show that 16.6% of the South Australian population have a hearing impairment in the better ear at 25 dbhtl and 22.2% in the worse ear at the same level. The results obtained in this representative sample compare well with those obtained in the British Study of Hearing, although some differences were observed. Conclusions Overall, there are only a few studies worldwide that have audiologically assessed the impairment of hearing from a representative population sample. The overall prevalence of hearing impairment in Australia is similar to that found in Great Britain, although there are some differences between the estimates of severity of impairment and some sex differences. The corroboration of the two studies reinforces the status of hearing impairment as the most common disability of adulthood. The present study also showed that there are a large number of Australians who may benefit from a more systematic community-based rehabilitation programme including the fitting of hearing aids. Secondly, the study identified the need for health goals and targets for hearing to be based on an epidemiological approach to the problem. Keywords Hearing, audiology, impairment, disability, prevalence, population survey Accepted 26 August 1998 Assessment of public health problems should be based on the best available epidemiological information if we are to accurately target solutions that make optimum use of scarce health resources. Hearing has been estimated to be the most prevalent disability in developed countries, 1 however, worldwide only a small number of hearing studies have provided estimates of a Centre for Population Studies in Epidemiology, Department of Human Services, PO Box 6, Rundle Mall, Adelaide, South Australia 5000, Australia. b 251 Morphett Street, Adelaide, South Australia 5000, Australia. c Department of Speech Pathology, Flinders University, Bedford Park, South Australia 5042, Australia. d MRC Institute of Hearing Research, University Park, Nottingham NG7 2RD, UK. e Family and Community Services, Department of Human Services, Hindmarsh Square, Adelaide, South Australia 5000, Australia. hearing impairment that are based on representative population samples and where impairment has been measured by standardized audiological methods. 1 9 Often, local decision making regarding health goals and targets for public health problems, like hearing impairment, is compromised by inadequate planning data. This is so because hearing studies have relied on convenience or clinic samples and, often, only self-reported hearing disability, or on using estimates derived from other geographical regions. Hitherto, in Australia, the epidemiological data available have been either self-report, and of little value in determining the public health priority of hearing impairment and/or guiding the investment of resources, or based on data derived in Great Britain Hearing loss can be a devastating disorder depending on its severity. At the extremes we can refer to the inability of Beethoven to hear the perfection of his own work or of the 247

2 248 INTERNATIONAL JOURNAL OF EPIDEMIOLOGY effect on Goya which may have contributed to his black painting period. 22 For most, though, hearing impairment is less traumatic but still strikes at a fundamental aspect of the individual s humanity: the ability to communicate effectively and subtly. Also, a considerable proportion of peoples information needs today relies on hearing via the telephone, radio and television. Hearing has also enjoyed a low medical and public health profile and this has not facilitated information on its true public health impact. Together with locomotor disorders, hearing disorders have been shown to top the English disability league for the number of life years affected. 23 Yet, Davis has shown that substantial gains can be achieved for people with moderate hearing impairment through appropriate fitting of hearing aids. 24 It is only as epidemiological studies, such as the British National Study of Hearing, provide accurate estimates of the problem that a true assessment of the impact can begin and service provision appropriately geared. This study was designed to provide reliable and representative estimates of hearing impairment for an adult Australian population and to compare these data with the British Study of Hearing, which had previously addressed the major epidemiological concerns outlined above in providing estimates of hearing impairment for Great Britain. 5 This study also makes a contribution to the few studies worldwide that have provided prevalence estimates from representative population samples and strengthens the hypothesis that it is the most common disability. Method This study used a two-stage sample design. Stage 1 involved a multistage clustered area sample of n = 9027 people aged 15 years (72% response rate) selected at random from South Australian households. In this process Australian Bureau of Statistics Census collectors districts were used as the sampling frame. First, collectors districts were systematically selected with probability of selection proportionate to their size. Within each collector district ten households were selected using a fixed skip interval from a random starting point. Within each household the person whose birthday was next was selected for interview and there was no replacement for non-respondents. A small variation was made to the sampling method in country regions where towns of 1000 population or more were selected prior to the selection of collectors districts. The survey vehicle is a biannual health survey known as the South Australian Health Omnibus Survey (SAHOS) in which respondents are interviewed about a range of health issues. The total sample of n = 9027 was selected in three consecutive SAHOS over a 12-month period. The people selected for interview were asked a preliminary screening question by an interviewer regarding their hearing. This was do you have trouble hearing what people say to you in a quiet room (a) when they speak loudly to you; (b) if they speak normally to you; (c) if they whisper to you; and, (d) none of these? People were considered to have a self-reported hearing disability if they answered yes to any of the first three categories and not having a self-reported hearing disability if they answered yes to the fourth category. The second stage of the survey involved an audiological assessment of hearing loss by one of eight audiologists. All participating audiologists had been trained in a workshop dealing with the study protocols, including: the calibration of all audiological equipment to Australian standards; history taking; the sequence of audiological examinations; recording of data on the study audiogram; translation of data for computer entry; and, appropriate referral of subjects with significant morbidity. Otoscopic examination was conducted for each ear and if significant cerumen was detected, which obscured a good view of the tympanic membrane, the participant was referred to their general practitioner for removal of the cerumen. A further appointment was made to complete the audiological assessment. All audiological assessment was performed in sound-attenuated booths, conforming to Australian Standard for measurement of air conduction thresholds of 0 dbhtl. A firm calibration protocol conforming to Australian Standards AS for air conduction and Australian Standards AS :1995 for bone conduction 27 was maintained throughout the study. Airconduction thresholds were obtained at 0.25, 0.5, 1, 2, 3, 4, 6 and 8 khz. Bone conduction thresholds were obtained at 0.5, 1, 2 and 4 khz. Home visits were conducted for 51 people in the sample who could not attend the audiologist. In these cases EAR TONE 3A insert earphones were used in conjunction with a portable audiometer conforming with the Australian standard. Following the self-reported hearing disability question of Stage 1, people were asked whether or not they would be prepared to be examined audiologically. Of the n = 9027 people interviewed in the SAHOS, n = 1378 (15.3%) reported a hearing disability. Of these, n = 689 (50%) completed the Stage 2 audiological examination. Of those reporting no hearing loss in the Omnibus Survey 75% agreed to attend for audiological assessment. Of these n = 300 were selected at random and asked to attend for audiological examination and n = 237 (79%) did so. This gives a final response rate for those reporting no disability of 59% ( ). Table 1 shows the response rates of the Health Omnibus Survey; the number recruited to Stage 2 and those finally examined at audiology. In all, 3.1% of people recruited to audiology were referred to their general practitioner for removal of cerumen prior to audiological assessment. This study therefore had a complex sampling design. The multistage sampling method of the SAHOS requires that the data are weighted by age, sex, household size, and part of state (country/metro). Re-weighting of the data was required in this hearing study in which people were first asked about their hearing in the SAHOS then recruited to the Stage 2 audiological assessment. Re-weighting of the data took into account the different probabilities of selection in each SAHOS, whether or not the respondents reported a hearing loss, and finally age, sex and part of state in which recruited. In re-weighting the data the South Australian age groups required to allow direct comparisons with the British National Study of Hearing were Table 1 Recruitment to the South Australian Health Omnibus Survey (SAHOS) and to the second stage audiological assessment of hearing Self-report Asked for Audiologically in the SAHOS audiology examined Impaired n = 1378 n = 1378 n = 689 (50.0) Not impaired n = 7649 n = 300 n = 237 (79.0) Total n = 9027 n = 1678 n = 926

3 HEARING IMPAIRMENT IN AUSTRALIA 249 years, years, years and 71+ years. There were two small variations between the British and Australian age categories. The youngest age category in the Australian data commenced at 15 years of age compared with 17 years in the National Study of Hearing. The 71+ age category for the British data truncated at 80 years of age, whereas the Australian data included all ages 71 years. As the number of cases 17 years and 80 years in the Australian data were small it is considered that these differences had marginal effect on the comparison of prevalence rates. Because of the complex sample design the most appropriate variance estimates are provided by the ultimate cluster variance estimator which calculates the total variance of the estimate based on the variation between sampling units. This estimator calculates the total variance of an estimate derived from a multistage sample. For each age- and sex-specific prevalence estimate the variance was derived from two sources and summed. These comprised both those who reported a hearing disability which was confirmed audiologically and those who reported no disability who were confirmed to have a hearing impairment when measured audiologically. For the purposes of the regression analysis people were classified according to the self-reported length of time they had been exposed to industrial noise in their occupation. Occupation was classified using the Australian Bureau of Statistics Standard Classification of Occupations (ASCO). 28 This listing was used to verify that the occupation would in fact be classifiable as noisy. Socioeconomic status (low, medium, high) was derived from ASCO classifications using a conventional method of aggregation. 29 Results To indicate expected difficulty with conversational speech the results of the Australian data were summarized over the frequencies 0.5, 1, 2 and 4 khz. The ears were classified as better or worse depending on this average score. Table 2 shows the prevalence for four severities of hearing impairment ( 25, 35, 45, 65 dbhtl) in the better and worse ears. Davis 5 has identified that the first and last two of these levels of impairment correspond to the lower boundaries of mild, moderate and severe impairment. It can be seen from Table 2 that 16.6% of adults have an impairment at 25 dbhtl, 6.9% an impairment at 35 dbhtl, 2.8% an impairment at 45 dbhtl and 0.5% an impairment at 65 dbhtl in both ears. Approximately 7.6% have a moderate hearing impairment in at least one ear, 2.8% in both ears. The prevalence of impairment is consistently higher in both the better and worse ears for males compared with females. If the worse ear is compared by sex, the point estimates for males is almost double that of females for each severity group 35 dbhtl. Although not shown in these Tables, there was less difference in the Great Britain estimates between males and females for both moderate and severe hearing impairment. Tables 3 and 4 show the data for the better and worse ear by age group and compare the estimates to the age-specific estimates for the British data. It can be seen that the overall prevalence in the better ear is comparable with the British estimate, although the level of severity is greater in the British population for people aged 70 years. It appears, however, that the South Australian estimates for moderate and severe hearing Table 2 Prevalence (%) of hearing impairment (db hearing threshold level averaged over 0.5, 1, 2, 4 khz) in the WORSE and BETTER ear for the South Australian population, by sex (n = 926) Worse ear (dbhtl) Gender Male n = 510 ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) Female n = 416 ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) Overall n = 926 ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) Table 3 Prevalence (%) of hearing impairment (db hearing threshold level averaged over 0.5, 1, 2, 4 khz) in the BETTER ear for South Australia (n = 926) and the United Kingdom (n = 2662), by age group South Australia United Kingdom Age group years n = 430 ( ) ( ) ( ) n = 1201 ( ) ( ) ( ) years n = 163 ( ) ( ) ( ) n = 695 ( ) ( ) ( ) years n = 174 ( ) ( ) ( ) n = 535 ( ) ( ) ( ) 71+ years n = 159 ( ) ( ) ( ) n = 277 ( ) ( ) ( ) Overall n = 926 ( ) ( ) ( ) n = 2708 ( ) ( ) ( )

4 250 INTERNATIONAL JOURNAL OF EPIDEMIOLOGY Table 4 Prevalence (%) of hearing impairment (db hearing threshold level averaged over 0.5, 1, 2, 4 khz) in the WORSE ear for South Australia (n = 926) and the United Kingdom (n = 2662), by age group South Australia United Kingdom Age group years n = 430 ( ) ( ) ( ) n = 1201 ( ) ( ) ( ) years n = 163 ( ) ( ) ( ) n = 695 ( ) ( ) ( ) years n = 174 ( ) ( ) ( ) n = 535 ( ) ( ) ( ) 71+ years n = 159 ( ) ( ) ( ) n = 277 ( ) ( ) ( ) Overall n = 926 ( ) ( ) ( ) n = 2708 ( ) ( ) ( ) impairment in the better ear catch up with the British population in the 70 age group. The Great Britain data show two age-specific differences from the Australian data in the better ear and one age-specific difference in the worse ear. The main difference observed is the overall estimate for severe impairment in the better ear, suggesting that disability in Great Britain may be slightly worse than Australia. In the SAHOS used to recruit the sample for this study the combined self-reported prevalence of hearing disability was 15.3%. This was not significantly different from the measured overall prevalence for the better ear (χ 2 = 1.1, d.f. = 1, P = 0.3). It is significantly different if the self-report rate is compared with the measured estimate for the worse ear (χ 2 = 1.6, d.f. = 1, P ). It is, however, not only statistical significance that should be considered in determining the value of selfreported hearing data. In this study there was considerable disagreement between self-reported and measured hearing status that was obscured when comparing only the overall prevalence rates. People classified themselves as hearing impaired, or not hearing impaired, according to the self-report question identified earlier. When measured audiologically, the false positive rate of the self-report question was found to be 46% and the false negative rate 17%. This means that on self-report there is a considerable misclassification problem even though the overall prevalence rates are similar. Given this information selfreported hearing disability cannot be considered valid for planning purposes. Table 5 shows the odds ratios from the additive main effects for the prevalence of average hearing impairment at 25 dbhtl and 45 dbhtl. Four variables, known to contribute to hearing impairment in other studies, were used in these analyses. These were: age, sex, socioeconomic status and length of time exposed to noise in their occupation. The logistic model proved a good fit of the hearing impairment data at 25 dbhtl (Hosmer & Lemeshow goodness of fit χ 2 = 3.04, d.f. = 8, P 0.93), and also at 45 dbhtl (Hosmer & Lemeshow goodness of fit χ 2 = 8.34, d.f. = 7, P = 0.3). It can be seen from Table 4 that the prevalence of hearing impairment at 25 dbhtl is affected significantly by age, sex and length of time exposed to noise. At the 45 dbhtl level, age and one category of noise exposure were significant. Table 5 Odds ratios from the logistic models showing the associations between variables of interest and hearing impairment at 25 dbhtl and 45 dbhtl Discussion Odds ratio n = 926 Factor 25 dbhtl 45 dbhtl Age group years (n = 430) years (n = 163) 5.6** 11.1** years (n = 174) 19.2** 18.0** 71+ years (n = 159) 123.9** 369.3** Sex Female (n = 416) Male (n = 510) 1.7* 1.7 Socioeconomic High (n = 382) status Medium (n = 287) Low (n = 243) Time exposed None (n = 460) to noise 1 10 years (n = 222) 2.1** 1.9* 11+ years (n = 243) 3.0** 2.6** *Significant at P = 0.05 level, **significant at the P = 0.01 level. Previous estimates for hearing impairment in South Australia (and Australia) had either used Australian data based on selfreport, or used data from Great Britain, which had audiometric assessment. This study has been able to obtain reasonably robust audiological data on a representative sample of the South Australian population. From the study, the best estimate of hearing impairment at 25 dbhtl, if the better ear is used, is 17% of the population aged 15 years. This decreases to 0.5% at 65 dbhtl. The data from this study provide the first valid representative population information for planning and resource investment in hearing outcomes for Australia. They also confirm the status of hearing impairment as the most frequent of disabilities. 1 Comparison with the British Study of Hearing was conducted mainly to provide a reference point for the Australian results with other data obtained in a high quality representative population sample and not to test any specific hypotheses. Hypothesis testing was possible, however, due to the different approaches

5 HEARING IMPAIRMENT IN AUSTRALIA 251 to obtaining representative samples in each of the surveys, 5 informal comparisons were made. The few age-specific differences that are observed between the overall Australian and Great Britain data may be real or could be due to differences in methodology. Despite this, considerable similarity is apparent in the prevalence of hearing impairment in both countries and the British audiological estimates can be viewed as corroborating the Australian audiological findings, or vice versa. Differences observed between the two countries are the prevalence comparisons between males and females. While the rates for Australian males were almost double those for females in the worse ear, the differences in Great Britain were not as large between sexes. This may reflect different aetiological and/or audiological history for British women. In the British Study manual socioeconomic status emerged as a significant explanatory variable. This was not the case in the Australian study and is most likely to be due to the different ways of classifying social class for each study. How do these estimates compare with previous Australian estimates? The best estimates to date are those provided in a 1991 self-report representative population survey of n = 2559 South Australians, which used the British Study self-report question and provided two estimates of 14.6% and 19.4%, depending on how hearing disability was defined in that study. 19 Despite the difference in aspects of methodology between the surveys, we can again make informal comparisons. As the estimates in the 1991 study were self-report it is not possible to say whether they apply to the better or worse ear or both. In testing the difference between the two studies, therefore, the audiological estimates obtained for the better and worse ears in the present study were compared with both of the 1991 self-report estimates. Only one comparison was statistically significant: that between the measured estimate in the worse ear of 22.2% in the present study, and the self-report estimate of 14.6% in the 1991 study (Z = 4.6). Again, however, it should not be concluded that self-reported estimates of hearing disability are a valid estimate of hearing impairment. As this study has shown, self-report can lead to a higher probability of false positives and false negatives. Consequently, the development of hearing policy based on self-report data is likely to be seriously flawed because of inaccurate descriptions of the target groups. The results of this study showed the prevalence of moderate hearing impairment at 35 dbhtl in the better ear was 6.9% and 12.0% in the worse ear. The first of these two estimates is a level of impairment at which people would usually benefit from wearing a hearing aid. 30 Across Australia 6.9% of people aged 18 years equates with people. A supplementary question in this survey showed that, at best, only 38% of this group used a hearing aid on a daily basis. The reasons for the failure to benefit from this technology is the subject of further investigation. The second of the prevalence estimates at 35 dbhtl, is a level of impairment where there is at least the need for education and aural rehabilitation that will modify handicap to the individual in some situations. Across Australia this service has largely been provided by small non-government hearing agencies, largely of the self-help variety, who operate on small budgets and are not resourced to the point where they can service the needs of the 1.6 million people who would be included in the second prevalence estimate. Both estimates now raise the need for an administrative framework that can consider a system wide approach to setting health goals and targets for hearing impairment, disability and handicap across Australia. Because of the differential response rates in this study a supplementary analysis was conducted to compare respondents and non-respondents. First all respondents to the Stage 2 audiological study were compared to all non-respondents by age, sex, and geographical area. No statistically significant differences were observed between the two groups overall. Comparison of response rates were also made for those who self-reported hearing impairment and those who self-reported no hearing impairment. This showed that people who reported no hearing impairment were younger. It is reasonable to suggest that younger people are more mobile and therefore more likely to respond to the offer of an audiological assessment and could therefore account for the higher response rates in the groups who self-reported no impairment. A final conclusion from this study relates to the epidemiology of hearing impairment worldwide. Given the increasing need to target health resources to achievable health outcomes, there have to date only been a handful of representative population studies in which hearing levels are assessed audiologically. If selfreported data are used for planning purposes, as has been the case in Australia, we have no clear understanding of whether selfreported disability is related to the better ear, the worse ear, or both. In addition, because of the false positive and false negative rates, we are unable to accurately assess the effects of impairment and disability on handicap. Davis 1 provides a comprehensive review of the domains of hearing disorders and proposes an epidemiological model for the investigation of hearing disorders in populations. The inherent lesson from his paper relates to the reliability and validity of data as the basis of policy and the development of interventions for hearing impairment, disability and handicap. Using Davis epidemiological model as the standard for population research on hearing there are few studies worldwide that would provide an adequate planning base for the most common of disabilities. The present study goes someway to redressing that situation. Acknowledgements This study received funding through a Public Health Research and Development Grant from the National Health and Medical Research Council. The authors also acknowledge the support of a number of South Australian audiologists without whom the data could not have been obtained. These were: Matthew Callaway, Ron Kendall, Sam Koroneous, Jill Hoggard, Kathy Holland and Tim Rayner. References 1 Davis AC. Epidemiology of hearing disorders. In: Kerr AG (ed.). Scott Brown s Otolaryngology. Boston: Butterworth Heineman, D Sousa MF, Irwig LM, Trevelyan HT et al. Deafness in middle age. J R Coll Gen Pract 1975;25: Milne JS. Hearing loss related to some signs and symptoms in older people. Br J Audiol 1976;10: Moscicki EK, Elkins EF, Baum HM, McNamara PM. Hearing loss in the elderly: an epidemiological study of the Framingham Heart Study cohort. Ear Hear 1985;6:

6 252 INTERNATIONAL JOURNAL OF EPIDEMIOLOGY 5 Davis AC. The prevalence of hearing impairment and reported hearing disability among adults in Great Britain. Int J Epidemiol 1989;18: Gates GA, Cooper JC, Kannel WB, Miller NJ. Hearing in the elderly: the Framingham cohort, Ear Hear 1990;11: Ostri B, Parving A. A longitudinal study of hearing impairment in male subjects an 8-year follow-up. Br J Audiol 1991;25: Cooper JC. Health and nutrition examination survey of Part 1. Ear and race effects in hearing. J Am Acad Audiol 1994;5: Quaranta A, Assennato G, Sallustio V. Epidemiology of hearing problems among adults in Italy. Scand Audiol 1996;42(Suppl.): Herbst KG, Humphrey C. Prevalence of hearing impairment in the elderly living at home. J R Coll Gen Pract 1981;March: Herbst KG, Meredith R, Stephens SDG. Implications of hearing impairment for elderly people in London and Wales. Acta Ololaryngol 1991;476(Suppl.): Gennis V, Garry PJ, Haaland KY, Yeo RA, Goodwin JS. Hearing and cognition in the elderly. Arch Int Med 1991;151: Sangster JF, Gerace TM, Sewald RC. Hearing loss in elderly patients in a family practice. Can Med Assoc J 1991;144: Slawinski EB, Hartel DM, Kline DW. Self-reported hearing problems in daily life throughout adulthood. Psychol Aging 1993;4: Evenhuis HM. Medical aspects of ageing in a population with intellectual disability: II. Hearing impairment. J Intellectual Disability 1995;39: Australian Bureau of Statistics. Hearing and the Use of Hearing Aids. Canberra: Australian Bureau of Statistics, 1978 (Catalogue No ). 17 Australian Bureau of Statistics. Australian Health Survey Canberra: Australian Bureau of Statistics, 1984 (Catalogue No ). 18 Australian Bureau of Statistics. Disability and Handicap Australia Canberra: Australian Bureau of Statistics, 1990 (Catalogue No ). 19 Wilson D, Xibin S, Read P, Walsh P, Esterman A. Hearing loss an underestimated public health problem. Aust J Public Health 1992; 16: Trumble SC, Piterman L. Hearing loss in the elderly. A survey in general practice. Med J Aust 1992;157: Ward JA, Lord SR, Williams P, Anstey K. Hearing impairment and hearing aid use in women over 65 years of age. Cross-sectional study of women in a large urban community. Med J Aust 1993;159: Vargas LM. The black paintings and the Vogt-Koyanagi-Harada syndrome. J Florida Med School 1995;82: Haggard M. Research in the Development of Effective Services for Hearing- Impaired People. Fifth HM Queen Elizabeth the Queen Mother Fellowship. Oxford: Burgess Ltd, Davis A, Stephens D, Rayment A, Thomas K. Hearing impairments in middle age: the acceptability, benefit and cost of detection (ABCD). Br J Audiol 1996;26: Standards Australia. Acoustics Hearing Conservation Australian Standards AS Canberra: Standards Australia. 26 Standards Australia. Australian Standard. Audiometers , Canberra: Standards Australia, Standards Australia. Acoustics Instrumentation for Audiometry. Part 4: A Mechanical Coupler for Calibration of Bone Vibrators : Canberra: Standards Australia. 28 Australian Bureau of Statistics. Australian Standard Classification of Occupations (First Edn.) Canberra: Australian Bureau of Statistics, Kelley JL, Evans MDR. Using ASCO for Socio-economic Analyses: Assessment and Conversion into Status and Prestige Indices. Research School of Social Sciences, Australian National University, Davis A, Stephens D, Rayment A, Thomas K. Hearing impairments in middle age: the acceptability, benefit and cost of detection (ABCD). Br J Audiol 1992;26:1 14.