Australian firm ResApp Health has seen positive results for a cough audio-based Covid-19 screening test that only requires a smartphone.

In an exploratory clinical trial of 741 patients, 446 of whom were Covid-19 positive, recruited in the USA and India, ResApp’s screening test, which uses machine learning to analyse the sound of a patient’s cough, was found to detect Covid-19 correctly in 92% of people with the infection.

ResApp will position this as a non-invasive, instant, smartphone-only screening test to rule out Covid-19 and be used prior to a rapid antigen or PCR test.

In the trial, the test achieved a sensitivity of 92%, which is said to be better than real-world data on rapid antigen tests, and a specificity of 80%. The combination of high sensitivity and 80% specificity results in eight out of ten people without Covid-19 being correctly screened as negative and not requiring a follow-on rapid antigen or PCR test.

The performance of the algorithm was obtained using K-fold cross-validation to provide an estimate of performance on unseen data. ResApp intends to submit the results for publication in a peer-reviewed journal in the coming weeks.

As a smartphone-based test, it is non-invasive, easy-to-use and instant; the entire test and results takes less than 30 seconds. The test also has unlimited scalability, no supply chain or distribution issues, and none of the environmental impacts of rapid antigen tests.

ResApp says it will target use in settings where frequent Covid-19 testing is required, such as employee, healthcare worker and student screening, travel, sports, entertainment, and aged care.

“The scale of this pandemic and the likely evolution to an endemic disease means we need more scalable diagnostic tools that can balance our current over-reliance on rapid antigen and PCR tests,” said Catherine Bennett, chair of epidemiology at Deakin University, and a member of ResApp’s Covid-19 scientific advisory board. “By rapidly ruling out Covid-19, ResApp’s Covid-19 test would significantly reduce the number of rapid antigen and PCR tests required, while still maintaining the disease surveillance needed to manage the continued impact of Covid-19. The simplicity, ease of use and unlimited scalability of ResApp’s test will be welcomed by public health officials around the world.”

Tony Keating, CEO of ResApp, added: “This non-invasive, smartphone test will offer a unique opportunity to provide a rule-out screening test for Covid-19 at scale across the world, delivering huge savings to government, insurers and the public as well as significantly reducing the environmental impact of rapid antigen and PCR tests. These results also build our confidence in the development of patient management and monitoring tools for Covid-19 and expanding our research into long-Covid.”