Self-rated smell ability enables highly specific predictors of COVID-19 status: a case control study in Israel

BACKGROUND: Clinical diagnosis of coronavirus disease 2019 (COVID-19) is essential to the detection and prevention of COVID-19 Sudden onset of loss of taste and smell is a hallmark of COVID-19, and optimal ways for including these symptoms in the screening of patients and distinguishing COVID-19 from other acute viral diseases should be established METHODS: We performed a case-control study of patients who were polymerase chain reaction-tested for COVID-19 (112 positive and 112 negative participants), recruited during the first wave (March 2020-May 2020) of the COVID-19 pandemic in Israel Patients reported their symptoms and medical history by phone and rated their olfactory and gustatory abilities before and during their illness on a 1-10 scale RESULTS:  Changes in smell and taste occurred in 68% (95% CI, 60%-76%) and 72% (95% CI, 64%-80%) of positive patients, with odds ratios of 24 (range, 11-53) and 12 (range, 6-23), respectively The ability to smell was decreased by 0 5 ± 1 5 in negatives and by 4 5 ± 3 6 in positives A penalized logistic regression classifier based on 5 symptoms had 66% sensitivity, 97% specificity, and an area under the receiver operating characteristics curve (AUC) of 0 83 on a holdout set A classifier based on degree of smell change was almost as good, with 66% sensitivity, 97% specificity, and 0 81 AUC The predictive positive value of this classifier was 0 68, and the negative predictive value was 0 97 CONCLUSIONS: Self-reported quantitative olfactory changes, either alone or combined with other symptoms, provide a specific tool for clinical diagnosis of COVID-19 A simple calculator for prioritizing COVID-19 laboratory testing is presented here