Abstract
BackgroundHearing impairment is currently the third largest cause of disability and affects over 1.57 billion people globally. The WHO estimates that 34 million children have hearing impairment but estimates for the prevalence vary depending on methodology, severity thresholds and age of testing. The 2021 Global Burden of Disease studies estimate 70 million children aged 0-15 years live with hearing loss (HL)6 . A meta-analysis reported a median prevalence of 7.7%. Amongst the highest reported community rates from an individual study was 24.5% amongst rural children aged 4-6 years in Malawi.
Hearing impairment in childhood impacts language, literacy, learning and confidence with lifelong educational and economic impacts. Management can include the use of assistive technology devices like hearing aids. The availability and quality of these are another source of inequality.
This thesis sought to clarify the feasibility of testing a possible frugal ‘off the shelf’ hearing device for adults and children in both high and low resource settings. The intention was to ultimately advocate for its use in settings where delays in accessing care (high and low resource) or limitations in provision of hearing devices (with low human and technological resource settings, namely Blantyre) mean that other alternatives are not currently available. Due to the potential impact through the life course of an early intervention for hearing health, where little alternative provision exists, the final elements of the thesis involved the piloting of such a device for children’s hearing health in urban Blantyre in Southern Malawi.
Methods
This thesis includes a meta-analysis of expected hearing thresholds for individuals with perforated tympanic membranes, which were expected in high numbers in the Malawian context. It also includes chapters based on primary UK studies including an evaluation of a frugal bone-conduction device with adults with known hearing impairment and a qualitative interview describing their experiences through the life course. Primary chapters conducted in Malawi include a cross-sectional epidemiological study of school age children in urban Blantyre and a mixed-methods, randomised, placebo-controlled cross-over pilot study of a direct-to-consumer bone conduction device.
Results
A systematic review of expected hearing threshold for those with tympanic membrane perforation or CSOM (our expected population of interest) predicted mean air conduction hearing thresholds of 48.3dBHL in adults and 31.9dBHL in children. Mean bone conduction thresholds were 26.6dBHL in adults and 9.5dBHL in children. The cross-sectional study found 12% prevalence of hearing impairment in school age children in urban Blantyre but the number who had conductive loss or perforated eardrums was lower than anticipated. The qualitative interviews with UK adults described “A changing relationship over time with deafness, themselves and society” and therefore a selection of mixed methods assessment tools was decided for the child studies including CHU9D, The Youth Quality of Life Instrument–Deaf and Hard of Hearing (YQOL-DHH), Digits in Noise (DIN) and a selection of visual analogue scores (VAS). A mixed methods study of acceptability and efficacy of a low-cost self-fitted bone-conduction device in UK adults with known conductive or mixed hearing impairment <50dBHL had a median speech score improvement of 11% with high acceptability. A pilot randomised prospective cross-over study of the impact of the bone conduction device for school-age children with mixed hearing impairment in Malawi found acceptability and safety but did not demonstrate an effect size, with few significant mean differences versus placebo.
Conclusion
Because of burden of disease and issues with healthcare access and affordability in Malawi, including low human resource for health, low wages and a highly rural population, an assessment was made of a frugal, low cost over the counter assistive technology that uses bone conduction. It was felt from initial literature reviews that given the high rate of conductive hearing loss, perforated tympanic membrane, otitis media and chronic suppurative otitis media in the school age population, that the device in question would be a suitable intervention for this population. A cross-sectional study found lower than anticipated prevalence of school age hearing loss in four urban Blantyre schools. This may represent an urban-rural divide with the superior health and socioeconomic status of children in the city, or indicate that children with hearing impairment are less likely to attend school. Very few children had access to assistive technology in this setting. We sought to explore impacts through the life course in adults in the UK who had previously identified hearing issues, and they identified the lasting impacts of hearing impairment at school age, continuing into adulthood, including how they wished to hide or control how they “display their deafness”. This meant that we sought to conduct a mixed methods evaluation of children to better describe their first-hand experience. The UK device study showed reasonable improvement for those adults with thresholds up to 50dBHL. However, the pilot study in children in Malawi failed to demonstrate a significant effect size in the primary outcome and although acceptability and safety was demonstrated, further studies are required. 15 These findings provide new insights regarding implementation of a similar frugal device for larger scale pilots with higher power. Recommendations are made for candidate selection (i.e. conductive loss with preserved sensorineural thresholds) and outcome selection (i.e. mixed methods assessment including generic and hearing specific quality of life scores and qualitative interviews), as well as device and delivery optimisation in partnership with local hearing health experts whether clinicians or D/deaf participants.
| Date of Award | 1 Jan 2025 |
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| Original language | English |
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| Supervisor | Graham Devereux (Supervisor), Kevin Mortimer (Supervisor), Mahmood Bhutta (Supervisor), Terry C Jones (Supervisor) & Wakisa Mulwafu (Supervisor) |