Adrian Davis

Screening for hearing loss in childhood: issues, evidence and current approaches in the UK

Until recently, screening for childhood hearing loss in the UK was based on two universal (i.e. whole population) screens: the infant distraction test screen at age eight months and the school entry hearing screen at age four to five years. Evidence reviewed in the 1990s indicated that the infant distraction test screen was seriously underperforming, but that (based on technology that had become available in the 1980s and 1990s) universal newborn hearing screening could be efficacious. At the same time, evidence was emerging on the importance and value of very early identification and intervention for permanent congenital childhood hearing loss. This led to the decision to implement a national newborn hearing screening programme (NHSP) in England and to phase out the distraction test at eight months. The initial implementation of the programme will be completed in 2005, and we summarize the evidence on the effectiveness of the first phase of the programme here. A number of important issues concerning childhood hearing loss and its management remain unresolved: the burden of late-onset and temporary childhood hearing losses, the most effective approaches to intervention and management, the case for screening for mild and/or unilateral hearing loss, and the role of the School entry screen. Some of the current research efforts to address these are outlined.

Hearing loss and paid employment: Australian population survey findings

This paper provides an analysis of participation in paid employment for people with a hearing loss over the full span of adult ages. The paper is based on original analysis of the 2003 Australian survey of disability, aging and carers (SDAC). This analysis shows that hearing loss was associated with an increased rate of non-participation in employment of between 11.3% and 16.6%. Advancing age and the existence of co-morbidities contribute significantly to reduced participation in employment. A disproportionate impact is evident for women and for those having low education and communication difficulties. Controlling for co-morbidities, hearing loss was associated with a 2.1% increase of non-participation in employment, a proportional difference of 1.4 times the population. People with hearing loss were less likely to be found in highly skilled jobs and were over-represented among low income earners. The SDAC data set provides self-report findings on the experience of disability rather than hearing impairment. As such, these findings serve as a conservative estimate of the impact of hearing loss on accessing well-paid employment.

Hearing in 44-45 year olds with m.1555A > G, a genetic mutation predisposing to aminoglycoside-induced deafness: a population based cohort study

Background The mitochondrial DNA mutation m.1555A>G predisposes to permanent idiosyncratic aminoglycoside-induced deafness that is independent of dose. Research suggests that in some families, m.1555A>G may cause non-syndromic deafness, without aminoglycoside exposure, as well as reduced hearing thresholds with age (age-related hearing loss). Objectives To determine whether adults with m.1555A>G have impaired hearing, a factor that would inform the cost–benefit argument for genetic testing prior to aminoglycoside administration. Design Population-based cohort study. Setting UK. Participants Individuals from the British 1958 birth cohort. Measurements Hearing thresholds at 1 and 4u2005kHz at age 44–45u2005years; m.1555A>G genotyping. Results 19 of 7350 individuals successfully genotyped had the m.1555A>G mutation, giving a prevalence of 0.26% (95% CI 0.14% to 0.38%) or 1 in 385 (95% CI 1 in 714 to 1 in 263). There was no significant difference in hearing thresholds between those with and without the mutation. Single-nucleotide polymorphism analysis indicated that the mutation has arisen on a number of different mitochondrial haplogroups. Limitations No data were collected on aminoglycoside exposure. For three subjects, hearing thresholds could not be predicted because information required for modelling was missing. Conclusions In this cohort, hearing in those with m.1555A>G is not significantly different from the general population and appears to be preserved at least until 44–45u2005years of age. Unbiased ascertainment of mutation carriers provides no evidence that this mutation alone causes non-syndromic hearing impairment in the UK. The findings lend weight to arguments for genetic testing for this mutation prior to aminoglycoside administration, as hearing in susceptible individuals is expected to be preserved well into adult life. Since global use of aminoglycosides is likely to increase, development of a rapid test is a priority.

Is the relation of social class to change in hearing threshold levels from childhood to middle age explained by noise, smoking, and drinking behaviour?

Recent work shows that variation in adult hearing function is related both to social class of origin and current social class. This study examines how much of this relationship after adjustment for childhood hearing impairment is explicable by occupational noise, current smoking, and alcohol consumption. A cohort of 9023 persons born in the UK during one week in 1958 was followed periodically, and hearing threshold levels (HTLs) were measured at 1 kHz and 4 kHz at age 45 years. Most (71% and 68%, at 1 kHz and 4 kHz respectively) of the relation to social class of origin of adult HTLs remains after adjustment for these other factors. For the relation to current social class, corresponding values are 64% and 44% (though varying by gender). The magnitude of social class effect is comparable to that of occupational noise. Susceptibility to hearing impairment is likely to be appreciably determined in early childhood.

Bilateral or unilateral amplification: is there a difference? A brief tutorial.

The literature contains many examples of the terms bilateral and binaural fittings used interchangeably (i.e., Carter, Noe & Wilson, 2001; Chmiel, et al, 1997; Dutt et al, 2002; Dermody & Byrne, 1995). In fact, however, humans are fit with hearing aids on either one ear (a unilateral fitting) or on both ears (a bilateral fitting), and generally, bilateral fittings have an impact on binaural hearing (the integration of two signals arriving from each ear independently). Standardization of this terminology should help to clarify future discussions and is essential to avoid confusion. The choice of when it is better to fit unilateral or bilateral hearing aids has been the subject of research, discussion and controversy for over fifty years (Carhart, 1946; Dirks & Carhart, 1962). It would seem a simple statement of fact and logic, that since humans have two ears, two ears wearing hearing aids would be better than one ear wearing one aid. However, evidence to date has not always been so factual, nor have the results been so logical. Dillon (2001) cites over 100 studies relevant to this topic. In 1999, 68% of hearing aid fittings in the U.S. were bilateral, up by 13% over the previous 10 years (Kochkin, 2000). Further, in 1999, prior to the modernized hearing aid plan, the United Kingdom (10 15%) and Finland (20%) fit fewer bilateral aids than Denmark (50 60%) and Norway (60%), with Sweden at 30% (Joint Nordic-British Project, 2001). Today, however, the number of bilateral fittings in England in some regions is 40% 80%. Why is there such variance? Shouldn’t everyone automatically receive and benefit from bilateral amplification? Unfortunately, the answer to that question is equivocal: some people benefit from two aids, and some do not. Generally speaking, hearing is the sensory system of import for oral communication, providing essential information about the environment that serves to alert and inform. Oft times these two functions interact. Thus, from a purely mechanical point of view, the ideal hearing aid enhances oral communication and permits perfect localization of sound in the environment. Consequently, tests for proper function of a hearing aid should include measures of speech intelligibility, sound quality (clarity, loudness, fullness, brightness, etc.), binaural redundancy (hearing the sound in both ears), noise tolerance and loudness discomfort levels as well as localization (in the vertical, lateral and horizontal planes). Further, consideration should be given to patient attitudes and physical comfort with the aid. The more normal the responses to all of these issues, the more satisfied the user and the more successful the fitting. Patients, as individuals, have unique auditory impairment and a unique set of personal, social, psychological and physical needs and characteristics. This means each fitting, and the results obtained from it, will be different, no matter how consistent the actual fitting process. Further, it should always be understood that any findings or opinions regarding the success or failure of any fitting may be completely independent of the actual benefit derived from the device itself. Measures of unaided versus aided threshold sensitivity are not good predictors of success. Two patients with similar degrees of threshold sensitivity often present with variant degrees of speech recognition in noise (Lyregaard, 1982). Patient attitudes, personality, the impact of the listening environment, perception of handicap and expectations from a hearing aid have all been significantly correlated to overall satisfaction and usefulness. So, even if formal audiometric measures do not show significant benefit from one fitting over another, the patient may feel otherwise (Humes, 1999; Cox & Alexander, 1999; Walden & Demorest, 1984). We know that audiometric measures do not reflect the value of a bilateral fitting. Real Ear Measurements, an excellent mechanism for determining the physical response of the ear itself, also do not adequately address questions of binaural interaction, how sound is perceived, comfort, or any of the myriad of psychological factors that could influence a successful outcome. Finally, current clinical procedures measure speech intelligibility and auditory localization. These excellent measures may not be entirely appropriate when assessing bilateral versus

Evaluation of a hearing screener

The objectives of the present study were to evaluate the compatibility of the hearing screener with pure tone audiometry and its capacity to predict the need and benefit of HAs. The device is a low-cost, easy to handle and safe instrument. It screens at 1 and 3 kHz at three different intensity levels. The outcome of the screen is categorized into six groups according to the number of tones heard and related to eventual fitting of HAs. One hundred and fifty persons (300 ears), with a median age of 65 years (range 20–86 years), consented to a hearing screen prior to pure tone audiometry, which was performed as part of the routine evaluation in the department. A comparative analysis of the pure tone audiometric thresholds and the screen thresholds showed that 27% of ears deviated >10 dB and 4%> 20dB at 1 kHz. At 3 kHz a deviation of >10dB was found in 34% and >20dB in 18%. The screen sensitivity was 92% related to persons and 89% related to ears, whereas the screen specificity was 65% and 62%, respectively. A PPV of 87% was indicated. The benefit of HAs was assured by the IOI-HA and SADL total scores of 3.9 and 4.0, respectively, with significant differences in the scores of the IOI-HA between the screened true and false positives. It is concluded that the screener has potential for use in developing countries and can be used as an alternative lean service delivery in developed countries.