«THE ECONOMIC IMPACT AND COST OF HEARING LOSS IN AUSTRALIA A report by Access Economics Pty Ltd February 2006 Listen Hear! The economic impact and ...»
Measurement of hearing loss: Hearing can be tested using either subjective or objective testing methods. Subjective testing includes standard audiometric testing, usually conducted by an audiologist or hearing aid audiometrist, or an ear, nose and throat specialist. In adults, this test consists of presentation of a series of tones (known as pure tones) or other speech or environmental sounds through a pair of headphones 2 The decibel standard was based on "the average threshold level of listeners at the Bell Telephone Laboratory" at a given time (Noble, 1978:176ff).
worn by the individual being tested. Each ear is tested separately. The presentation level of the sound (in decibels) is varied, and the individual reports the lowest level of sound that they can hear at a number of individual frequencies (usually encompassing the range from 250-8,000 Hertz). In young children, audiometric testing is conducted using a variety of sounds and estimating threshold from the behavioural responses observed. Objective testing does not require a subjective response from the individual.
Rather, objective tests measure a physiological response from the individual. For example the hearing of newborn children can be measured using the auditory brain stem response technique or other electrophysiological measures of the neural response to an acoustic stimulus. These objective techniques can also be used in adults to measure thresholds or to help identify the site of lesion of a hearing loss.
Figure 2-2 depicts the audiogram with degrees of disability (mild, moderate, severe and profound) represented (these differ slightly in the diagram from the definitions of mild, moderate and severe used elsewhere in this report).
Just as noise levels doubled in intensity for each increase of 6dB, a person’s hearing acuity is halved for each 6 dB deficit in hearing threshold.
Source: CRC Hear – the red X line represents the hearing test for the left ear and red O line for the right ear. Note: severity categories differ slightly in the diagram from the definitions of mild, moderate and severe used elsewhere in this report.
Figure 2-3 depicts the audiogram and shows where key sounds fall by frequency and intensity. Overlaid on this audiogram is the result of a hearing test (pale red line for left ear and dark red line for right ear). In the left ear the audiogram depicts a hearing loss that is moderate by degree in the lower frequencies moving to profound in the higher frequencies. The hearing in the right ear is within the normal range. The level of hearing loss reported is commonly taken as an average of the three frequencies (500
Hz, 1,000Hz and 2,000 Hz). The audiogram in this example would be reported as normal in the right ear and moderate in the left ear. Taking measures of the better ear, this person would not be counted as having a hearing disability.
2.3 CAUSES OF HEARING LOSS Figure 2-4 depicts the hearing system; highlighting places within the ear where hearing loss occurs (see below).
The inability to hear generally stems from one of two causes.
Conductive hearing loss occurs when problems in the middle ear prevent it from conducting sound to the inner ear. A conductive loss can be transient or permanent. The most common cause of hearing loss in children is Eustachian tube dysfunction, which may affect up to 30% of children during the winter months. This problem, which all people may experience in terms of hearing loss associated with a severe head cold, may lead on to more serious problems such as fluid in the middle ear or the more serious otitis media, in which a bacterial or viral agent infects the middle ear or the ear drum. Otitis media may result in perforations of the ear drum as well. The level of hearing loss associated with this condition is approximately 40dB. More chronic types of otitis media can result in permanent scarring of the ear drum. Such scarring reduces the ability of the ear drum to respond to sound and hence the sound is not conducted well through the ossicular chain to the inner ear. Other forms of conductive loss can result from damage to the ossicular chain, which in some cases can ossify (harden into bone).
Sensorineural hearing loss, the second type of deafness, results from damage within or malformation of the cochlea itself, where the hairs cells are either damaged or destroyed. Injury to the hair cells can result from excessive noise exposures, chemical damage such as smoking (Nomura et al, 2004),
environmental agents (Rybak, 1992) or medications (Buszman, 2003), and long term wear and tear from the ageing process, which is referred to as presbycusis.
Hearing loss can also result from damage to the auditory or eighth nerve that runs from the cochlear to the brain – hence the term sensorineural. Sensorineural hearing loss is permanent by nature.
A smaller number of people can have a mixed hearing loss, where part of the hearing loss results from a conductive loss and part from sensorineural loss.
The first and primary impact of hearing loss is on the perception of usable information by the individual. Any disruption to this cascade of sounds, as they move from the environment through the various parts of the ear to the auditory nerve and on to the brain, poses a threat to the individual being able to hear and in turn to learn to recognise these sounds as speech and usable language. Hearing loss can impact on speech in adults who suffer a sudden and complete sensorineural hearing loss, but also particularly in children, as the motor pathways that control speech have a critical period for development that is thought to be within the first 5-7 years of life. Hearing loss in children also impacts on the acquisition of language and vocabulary, which may have a lifelong impact on educational and employment opportunities. Figure 2-5 summarises the relationship between speech and language.
The impact of hearing loss in a person’s life depends on the intersection of three key factors – the time a person acquires their hearing loss, the severity of the hearing loss, and the communication demands facing the person at their particular point of the life span. Hearing loss has a very specific impact on children, for example, who, while
representing a very small proportion of the population of people with hearing loss, require significant support in developing language and accessing education and employment.
Hearing loss in children is commonly congenital (the child is born with it) and sensorineural in nature. The cause can be genetic or arise though maternal infections or birth problems. A number of sensorineural losses also arise in children from infections such as meningitis occurring in early life. Conductive losses are also quite common, resulting from Eustachian tube dysfunctions and otitis media discussed in the previous section. Hearing loss, even of a mild nature, can have serious educational implications for children.
Hearing loss in adults is predominantly sensorineural in nature commonly caused by the ageing process and excessive noise exposures resulting from occupational or recreational noise. As the Beaver Dam study reported, hearing loss is associated with increasing age (Cruickshanks et al, 1998). Thus, as the Australian population ages, there will be increasing numbers of people with hearing loss. Some of the causal factors associated with hearing loss, such as ototoxic substances (i.e. chemicals that damage or destroy the hair cells), are not as yet well understood, limiting prevention efforts in this area. However, some conditions, such as noise induced hearing loss (NIHL), are preventable (see next Section 2.3.3).
Hearing loss in the Aboriginal community is very common. A systematic review of evidence commissioned by the Office of Aboriginal and Torres Strait Islander Health (OATSIH) reported that ear disease (particularly otitis media) and subsequent hearing loss were significant problems among Aboriginal communities. 3 Data quality problems and differing prevalence rates across regions limit the extent to which the problem can be credibly reported. The prevalence of otitis media in children was reported to vary between 10% and 54%. By United Nations criteria, a prevalence exceeding 4% is considered to be a significant public health problem. Subsequent perforated ear drums were reported to be between 9% and 35% and as high as 95% in some studies. Otitis media was occurring in newborn children with two thirds of babies having one ear drum affected by six months of age. Rates of hearing loss were reported between 10%-41%.
Hearing loss in comparative western populations was reported at between 5% and 7%.
Within the burden of disease model, otitis media is treated as a respiratory condition.
Costs associated with this ear disease in itself are therefore correctly excluded from this study. However, where hearing loss results, associated costs are included. For example, Australian Hearing and Office of Hearing Services data reported later in this study includes services for Aboriginal people with hearing loss. The spread of costs by ethnicity may be more important in certain areas. In the Northern Territory, for example, it is estimated that 60% of people with hearing loss are Aboriginal (Central Australian Aboriginal Congress, 2005). However, assessment of costs by ethnicity was outside the scope of this brief.
Time of onset: A person can acquire a degree of deafness at any age. The timing of onset has a direct bearing on the type of language skills a person may develop, the education s/he may receive and the type of employment opportunities available which s/he may access. As such, time of onset (coupled with degree of deafness) serves as 3 http://www.health.gov.au/internet/wcms/publishing.nsf/content/health-oatsih-pubs-omp.htm/$FILE/oc1.pdf
a critical marker with regards to service requirements and, potentially, lifetime costs.
There are two critical onset markers – pre and post lingual deafness.
The early identification of the onset of hearing loss at birth and/or prior to the development of spoken language (pre-lingual deafness) serves as a critical flag for the child’s future. Decisions are subsequently made with regard to the mode of communication to develop (sign language and/or speech), technologies to use (hearing aids, cochlear implants, and/or telephone typewriters (TTYs)), support services required (eg speech therapy, sign language interpreters) and the types of educational settings s/he may in turn access (such as early intervention programs, schools for the deaf, deaf support classes or mainstream classrooms).
Costs and opportunities are associated with the decisions made as are life opportunities for affected individuals. The impact of hearing loss on educational outcomes is evident in research, which indicates that young deaf people leave school with significantly lower educational outcomes than their hearing peers (Yoshinaga-Itano et al, 1998).
Post-lingual onset of deafness means that the person has acquired hearing loss after they have developed a language system. Following the onset of deafness, most people continue to use spoken language, supported by hearing devices and pursue a hearing culture, although a small number of people make the transition into the Deaf Community (see Section 2.4) and become sign language users.
NOISE INDUCED HEARING LOSS (NIHL)2.3.3
Wilson et al (1998:34) reports that a noise component was associated with 37% of the population of people with hearing loss. That is, for 37% of people with hearing loss, noise was responsible for at least part of their hearing loss. The most common sources of noise injury are workplace noise and recreational noise (personal stereos, domestic use of power tools, motor sports), although the attributable fractions for each have been debated.
RECREATIONAL HEARING LOSS (RHL)22.214.171.124
Sufficient exposure to recreational noise may result in recreational hearing loss (RHL).
Music exposure has been an issue for four decades – from rock and roll in the 1960s and 1970s, to walkmans in the 1980s and 1990s and more recently the emergence of MP3 players. However, the significance attributed to recreational noise by advocates and the media may be disproportionate to the risk. This may result in part because personal stereo systems are such a ubiquitous part of modern life. Apple, for example, advises that there are 28 million iPods in use worldwide. Despite such widespread use, there is no epidemiological data that systematically examines RHL, although there are studies that show short term or minor hearing damage resulting from personal stereo systems and music exposure generally. However, there have been no long term studies that document exposure outcomes resulting in permanent measurable and significant hearing loss eg 25 dB. Moreover, there is as yet no consensus on the contribution RHL makes to the overall prevalence of hearing loss (Mostafapour et al,
1998) and, indeed, in studies that have examined the contribution of recreational noise in the context of assessing people exposed to workplace noise, the contribution of other sources had been found to be so low as to be of minor consideration within calculations (see for example Neitzel et al, 2004). Finally, even where it was proposed that other conditions such as Ottis Media possibly made subjects more vulnerable to RHL, one study found this not to be the case (de Beer et al, 2003).
Recreational noise can cause hearing loss if the extent of exposure is loud enough and people are exposed over sufficient years (Williams, 2005b). While there is evidence that personal stereo system exposures are loud enough (Williams, 2005a) there is no evidence that exposures occur over a long enough period. A prospective study to this end is indicated. Rather recreational exposures appear to occur within a specific part of the life cycle (Serra et al, 2005) and not for the prolonged periods that would be required to sustain hearing loss (Williams 2005a). Studies linking substantial threshold shift (i.e. increases in hearing impairment) in the population with music are not there.