You sit down to tuck into a piping hot plate of char kway teow, but something’s not quite right. That familiar savoury smell is missing, and the first bite is far from satisfying. The sudden loss of smell, or anosmia, is now globally recognised as an early telltale sign of COVID-19.
To public health authorities, this curious symptom represented a potentially powerful approach for blocking the spread of infections; those experiencing anosmia could promptly get tested and self-isolate.
However, self-reported loss-of-smell accounts need to be confirmed with follow-up clinical tests, most of which were cumbersome and expensive, and cannot be re-used, said Ciarán Forde, a Senior Principal Investigator at A*STAR’s Clinical Nutrition Research Centre (CNRC).
Forde and colleagues envisioned a more practical and reliable alternative. “Our approach was to develop a rapid and cheap self-administered test that a person suspecting they had lost their sense of taste and smell could use to repeatedly test over time,” he said.
Unfortunately, the team’s research path was fraught with (pandemic-related) obstacles: faced with strict social-distancing mandates, Forde and his collaborators had to conduct their study entirely over Zoom. The researchers chose a panel of easy-to-recognise smells, such as mango and detergent, and taste-tested flavours that spanned the five basic tastes from bitter to sour.
Dubbed the Singapore Smell and Taste Test (SSTT), participants’ test package included an easy-to-follow poster, 'odour pens' and sachets of powdered taste tests. The poster also featured a QR code that users could scan to register their daily results remotely on their smart phones.
The team tested the effectiveness of the SSTT in COVOSMIA-19, a clinical trial in a cohort of 99 Singaporeans, 72 of whom tested positive for COVID-19. Most participants gradually stopped entering their data over the 28-day trial, which the team suggests could be because most recover their senses within a week of infection, reducing the incentive to continue testing.
Nevertheless, by comparing participants’ self-reported changes in taste and smell in questionnaires with their SSTT results, the team determined that these symptoms signal the beginnings of a COVID-19 infection.
“We concluded that ‘If you can’t smell, you’re not well’ is a good mantra to present for a COVID-19 PCR test to confirm a suspected COVID-19 infection,” Forde said, adding that future studies should include incentives and feedback loops to boost participant engagement.
The A*STAR-affiliated researchers contributing to this research are from the Clinical Nutrition Research Centre (CNRC).