Hearing screening with the digits-in-noise test : evaluating a national test and new stimulus approach

Abstract

The prevalence of hearing loss is high, affecting 1.3 billion people globally. Most persons with disabling hearing loss reside in low-and-middle-income countries (LMICs) where current hearing healthcare systems are insufficient to meet the need for services. To decentralise hearing loss detection the digits-in-noise (DIN) test was released in South Africa as a smartphone application, called hearZA. The test corresponds well with pure tone audiometric thresholds with high sensitivity and specificity. However, in a binaural test setup designed to make the test more efficient, the DIN is not sensitive to detect unilateral or severely asymmetric hearing loss. Sequential testing of each ear would double test time and possibly reduce test uptake by consumers. The study retrospectively analysed 24072 DIN tests, completed between March 2016 and August 2017, to determine characteristics of hearZA App users and predictors of test performance. Furthermore, in a comparative within-subjects research design, the study determined if dichotic speech could improve the sensitivity of the DIN test compared to conventional diotic speech. Adults with normal hearing (n=51; pure tone average thresholds (PTA) ≤ 25 dB HL in both ears), symmetric sensorineural hearing loss (n=47; PTA ≥ 26 dB HL) and asymmetric sensorineural hearing loss (n=24; PTA ≥ 26 dB HL in the poorer ear) were recruited. Overall referral rate of the hearZA DIN test was 22.4%, and 37% of these reported a known hearing difficulty. Age distributions showed that 33.2% of listeners were 30 years and younger, 40.5% were between 31 and 50 years, and 26.4% were older than 50 years. Age, self-reported English-speaking competence and self-reported hearing difficulty were significant predictors of the SRT. Furthermore, dichotic digit presentation markedly improved sensitivity of the DIN test to unilateral, asymmetric and symmetric sensorineural hearing loss. Dichotic testing Receiver Operating Characteristic area under the curve (0.94), and linear regression slope (0.18) and correlation (0.84) with SRT were higher than diotic (0.84, 0.08 and 0.79 respectively). High test uptake, particularly among younger users and high overall referral rate indicates that the hearZA App addresses a public health need. Furthermore, accurate detection of hearing loss is possible using a dichotic test paradigm. Population-wide access to the dichotic DIN test provides a promising prospect to address undetected hearing loss by making detection accessible and affordable.