The best COVID-19 predictor is recent smell loss: a cross-sectional study
Authors: Gerkin Richard C. , Ohla Kathrin , Veldhuizen Maria G. , Joseph Paule V. , Kelly Christine E. , Bakke Alyssa J. , Steele Kimberley E. , Farruggia Michael C. , Pellegrino Robert , Pepino Marta Y. , Bouysset Cédric , Soler Graciela M. , Pereda-Loth Veronica , Dibattista Michele , Cooper Keiland W. , Croijmans Ilja , Di Pizio Antonella , Ozdener M. Hakan , Fjaeldstad Alexander W. , Lin Cailu , Sandell Mari A. , Singh Preet B. , Brindha V. Evelyn , Olsson Shannon B. , Saraiva Luis R. , Ahuja Gaurav , Alwashahi Mohammed K. , Bhutani Surabhi , D’Errico Anna , Fornazieri Marco A. , Golebiowski Jérôme , Hwang Liang-Dar , Öztürk Lina , Roura Eugeni , Spinelli Sara , Whitcroft Katherine L. , Faraji Farhoud , Fischmeister Florian Ph.S , Heinbockel Thomas , Hsieh Julien W. , Huart Caroline , Konstantinidis Iordanis , Menini Anna , Morini Gabriella , Olofsson Jonas K. , Philpott Carl M. , Pierron Denis , Shields Vonnie D.C. , Voznessenskaya Vera V. , Albayay Javier , Altundag Aytug , Bensafi Moustafa , Bock María Adelaida , Calcinoni Orietta , Fredborg William , Laudamiel Christophe , Lim Juyun , Lundström Johan N. , Macchi Alberto , Meyer Pablo , Moein Shima T. , Santamaría Enrique , Sengupta Debarka , Dominguez Paloma Rohlfs , Yanik Hüseyin ,   GCCR Group Author, Hummel Thomas , Hayes John E. , Reed Danielle R. , Niv Masha Y. , Munger Steven D. , Parma Valentina ,   Non-byline authors (to be listed as collaborators in PubMed under the GCCR Group Author)
Published: July 2020

Background

COVID-19 has heterogeneous manifestations, though one of the most common symptoms is a sudden loss of smell (anosmia or hyposmia). We investigated whether olfactory loss is a reliable predictor of COVID-19.

Methods

This preregistered, cross-sectional study used a crowdsourced questionnaire in 23 languages to assess symptoms in individuals self-reporting recent respiratory illness. We quantified changes in chemosensory abilities during the course of the respiratory illness using 0-100 visual analog scales (VAS) for participants reporting a positive (C19+; n=4148) or negative (C19-; n=546) COVID-19 laboratory test outcome. Logistic regression models identified singular and cumulative predictors of COVID-19 status and post-COVID-19 olfactory recovery.

Results

Both C19+ and C19-groups exhibited smell loss, but it was significantly larger in C19+ participants (mean±SD, C19+: -82.5±27.2 points; C19-: -59.8±37.7). Smell loss during illness was the best predictor of COVID-19 in both single and cumulative feature models (ROC AUC=0.72), with additional features providing negligible model improvement. VAS ratings of smell loss were more predictive than binary chemosensory yes/no-questions or other cardinal symptoms, such as fever or cough. Olfactory recovery within 40 days was reported for ∼50% of participants and was best predicted by time since illness onset.

Conclusions

As smell loss is the best predictor of COVID-19, we developed the ODoR-19 tool, a 0-10 scale to screen for recent olfactory loss. Numeric ratings ≤2 indicate high odds of symptomatic COVID-19 (4<OR<10), which can be deployed when viral lab tests are impractical or unavailable.