An international team created a mobile device app that allows users to report repeatedly on symptoms thought to be relevant for COVID-19 and to self-report results of reverse transcription polymerase chain reaction (RT-PCR) testing for SARS-CoV-2. The app has been used by more than 2.6 million people in the U.K. and U.S. who believed they had symptoms of COVID-19. Of about 18,500 participants who underwent RT-PCR testing, about 7,000 tested positive.
Loss of smell and taste were much more common in participants who were RT-PCR positive than in those who were RT-PCR negative (65% vs. 22%; odds ratio, 6.74); results were similar regardless of country of domicile, age, or sex. These two symptoms best discriminated test-positive from test-negative participants, although several other symptoms — particularly fatigue and skipped meals — also were significantly more common in the test-positive participants.
This study involves self-selected participants who self-reported various symptoms; there was no formal testing of smell and taste. Nevertheless, the study provides strong evidence that loss of smell and taste are associated with COVID-19. However, one third of people with COVID-19 do not report these symptoms.