Prevalence of acquired or “late” deafness
Although it has been over 20 years since the last major deaf census, the best estimate we have is that 75% of deaf adults became deaf after the age of 19 <Schein & Delk, 1974>. The rate of deafened adults in the National Deaf Census (Schein & Delk) was 670/100,000 population, or about 1 in every 150 people. In Canada’s 1997 population of 30 million for example <Statistics Canada>, this translates to 201,000 deafened adults, and in Ontario, 76,380 deafened adults. In a United States population of 258 million in 1993 <Statistics Canada> that would project 1,728,600 deafened adults in the United States! (The Association of Late-Deafened Adults consistently has had fewer than 500 paying members, including some residing outside the US population base.)
A major criticism of the body of research on deafened adults, and “adventitious” or “acquired” hearing loss, is that the definitions have been inconsistent. Some major studies have included subjects with only moderate hearing losses, drawn from rosters of hearing aid clinics. This “dilutes” the sample with people who may be able to cope quite well with substantial residual hearing, placing the profound subjects in a small minority. Those with the most profound degrees of hearing loss and no interest in hearing aids would not have been included at all.
Many of the historical causes of both congenital and adventitious deafness have changed in incidence over the years. Infant and child illnesses are better prevented, diagnosed, and treated, while industrial and environmental noise sources increase and hectic modern society includes many ways a person could sustain traumatic injury. At the same time, genetic screening for causes of late-onset deafness, such as NF-2, is more available, and public health programs may reduce the incidence of bacterial and viral causes of deafness. A new survey would be needed to see how the proportions have been affected.
I also remain concerned about neglecting deafened adolescents. “Hearing loss in adults” has been used as a synonym for late-deafness. I was deafened before the age of 19 and would be classified as “prevocationally deaf” in the deaf census population proportions, yet from the perspective of adjustment, I clearly fit into the deafened rather than “born deaf” category.
Prevalence across classifications
The chart illustrates the rates of different causal classifications among deafened people. A 1984 survey of over 100 people by the National Association of Deafened People (NADP) in the U.K. indicated that 13.4% were deafened from congenital/familial causes, 57.7% from medical and surgical causes, and 3.9% from accidents <Heath, 1987>. Among 348 responses from members of the Association of Late-Deafened Adults (ALDA) in 1994/1995, 41.5% reported experiencing progressive losses including the apparently hereditary, 40.5% had medical losses, 12.8% had surgical losses, and 5.2% became deaf as a result of traumatic injury <Boone & Scherich, 1995>. These figures should be interpreted cautiously. The samples were not drawn from the general population; to be included in these samples, someone had to already be a known deafened person on a mailing list somewhere. People hiding in their closets afraid to go out and other isolated deafened people are not going to receive questionnaires in this type of study. If any type of deafness was more likely to cause people to withdraw from others, the proportions of that type could be underrepresented. The memberships of deafened and other deaf organizations are a tiny fraction of the population, as estimated from the proportions found in the National Deaf Census.
Hearing loss is usually described by hearing health professionals as ‘conductive’, ‘sensorineural’ or mixed. Conductive hearing losses are those which result from some gumming-up of the mechanisms, from wax buildup, broken eardrum, arthritis in the inner ear bones, etc. A sensorineural hearing loss (‘nerve deafness’) results when the nerves go on the fritz. Sometimes the nerves deteriorate, and this may occur in only one bunch of nerves, resulting in a frequency range with poor hearing and leaving other frequencies undamaged. A mixed hearing loss occurs when some of both things happen.
We generally find that this talk of sensorineural and conductive is not very informative for deafened people other than to deal with the need to have a name to explain what has happened. In general, however, “you have a sensorineural hearing loss” provides this benefit for about the length of time it takes to get to the doctor’s parking lot. That information does not tell the individual why it happened, and even if the reason is “you were hit on the head and all the bones in your inner ear crumbled to dust” it doesn’t answer the question, why was I hit in the head? Or, why did I go there that day? These questions may be what really underlie the search for the diagnosis. Even the most detailed diagnosis doesn’t help the individual to evaluate his feelings about his condition, in particular, how normal those feelings are.
In contrast, the terms medical, surgical, progressive and traumatic can be helpful because they embody the experience of change and where the change came from. In medical losses, the person has the accompanying illness and either the illness or the medications causes the deafness. In surgical losses, the person often has foreknowledge that deafness will result from the surgery they must have (e.g. to remove a nerve tumour). In progressive losses, health is good, except there is this contant, gradual change in what the person is able to hear. Medical losses can be progressive too, but usually occur over shorter times (perhaps 5 years). Progressive losses often take 20 years or more. Traumatic losses involve some kind of head injury, and are sudden. Usually when there is a head injury, there are other problems to deal with. For further descriptions of the experiences of ‘medical’, ‘surgical’, ‘progressive’, and ‘traumatic’ routes to deafness, see elsewhere on this site.
References
J. Schein and M. Delk, The deaf population of the United States. (Silver Springs MD: National Association of the Deaf, 1974). <back>
Statistics Canada, Canadian Statistics—Population, Canada, the provinces and territories. (1998) http://www.statcan.ca/english/Pgdb/People/Population/demo02.htm <back>
Statistics Canada, Canadian Dimensions—Population, population density, births and deaths for selected countries, 1993. (1998) http://www.statcan.ca/english/Pgdb/People/Population/demo01.htm <back>
A. Heath, ‘The deafened: a special group,’ In J.G. Kyle, Ed., Adjustment to acquired hearing loss. (Bristol UK: University of Bristol, Centre for Deaf Studies, 1987), pp. 163-168. <back>
S. Boone and D. Scherich, ‘Characteristics of ALDAns: The ALDA Member Survey.’ ALDA News, (Fairfax VA: Association of Late-Deafened Adults, 1995), p. 1. <back>
