Recent Smell Loss Is the Best Predictor of COVID-19 Among Individuals With Recent Respiratory Symptoms
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 Mehmet 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 , Dar Hwang Liang , 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 , Rohlfs Dominguez Paloma , Yanik Hüseyin , Hummel Thomas , Hayes John E , Reed Danielle R , Niv Masha Y , Munger Steven D , Parma Valentina ,   GCCR Group Author, Boesveldt Sanne , de Groot Jasper H B , Dinnella Caterina , Freiherr Jessica , Laktionova Tatiana , Marino Sajidxa , Monteleone Erminio , Nunez-Parra Alexia , Abdulrahman Olagunju , Ritchie Marina , Thomas-Danguin Thierry , Walsh-Messinger Julie , Al Abri Rashid , Alizadeh Rafieh , Bignon Emmanuelle , Cantone Elena , Paola Cecchini Maria , Chen Jingguo , Dolors Guàrdia Maria , Hoover Kara C , Karni Noam , Navarro Marta , Nolden Alissa A , Portillo Mazal Patricia , Rowan Nicholas R , Sarabi-Jamab Atiye , Archer Nicholas S , Chen Ben , Di Valerio Elizabeth A , Feeney Emma L , Frasnelli Johannes , Hannum Mackenzie E , Hopkins Claire , Klein Hadar , Mignot Coralie , Mucignat Carla , Ning Yuping , Ozturk Elif E , Peng Mei , Saatci Ozlem , Sell Elizabeth A , Yan Carol H , Alfaro Raul , Cecchetto Cinzia , Coureaud Gérard , Herriman Riley D , Justice Jeb M , Kaushik Pavan Kumar , Koyama Sachiko , Overdevest Jonathan B , Pirastu Nicola , Ramirez Vicente A , Roberts S Craig , Smith Barry C , Cao Hongyuan , Wang Hong , Balungwe Birindwa Patrick , Baguma Marius 
Published: December 2020

In a preregistered, cross-sectional study, we investigated whether olfactory loss is a reliable predictor of COVID-19 using 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 univariate and multivariate predictors of COVID-19 status and post-COVID-19 olfactory recovery. 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 univariate and multivariate models (ROC AUC = 0.72). Additional variables provide negligible model improvement. VAS ratings of smell loss were more predictive than binary chemosensory yes/no-questions or other cardinal symptoms (e.g., fever). Olfactory recovery within 40 days of respiratory symptom onset was reported for ~50% of participants and was best predicted by time since respiratory symptom onset. We find that quantified smell loss is the best predictor of COVID-19 amongst those with symptoms of respiratory illness. To aid clinicians and contact tracers in identifying individuals with a high likelihood of having COVID-19, we propose a novel 0–10 scale to screen for recent olfactory loss, the ODoR-19. We find that numeric ratings ≤2 indicate high odds of symptomatic COVID-19 (4 &lt; OR &lt; 10). Once independently validated, this tool could be deployed when viral lab tests are impractical or unavailable.