Smell dysfunction: a biomarker for COVID‐19

Background Severe acute respiratory syndrome‐coronavirus‐2 (SARS‐CoV‐2), the virus that causes coronavirus disease 2019 (COVID‐19), is responsible for the largest pandemic since the 1918 influenza A virus subtype H1N1 influenza outbreak. The symptoms presently recognized by the World Health Organization are cough, fever, tiredness, and difficulty breathing. Patient‐reported smell and taste loss has been associated with COVID‐19 infection, yet no empirical olfactory testing on a cohort of COVID‐19 patients has been performed. Methods The University of Pennsylvania Smell Identification Test (UPSIT), a well‐validated 40‐odorant test, was administered to 60 confirmed COVID‐19 inpatients and 60 age‐ and sex‐matched controls to assess the magnitude and frequency of their olfactory dysfunction. A mixed effects analysis of variance determined whether meaningful differences in test scores existed between the 2 groups and if the test scores were differentially influenced by sex. Results Fifty‐nine (98%) of the 60 patients exhibited some smell dysfunction (mean [95% CI] UPSIT score: 20.98 [19.47, 22.48]; controls: 34.10 [33.31, 34.88]; p < 0.0001). Thirty‐five of the 60 patients (58%) were either anosmic (15/60; 25%) or severely microsmic (20/60; 33%); 16 exhibited moderate microsmia (16/60; 27%), 8 mild microsmia (8/60; 13%), and 1 normosmia (1/60; 2%). Deficits were evident for all 40 UPSIT odorants. No meaningful relationships between the test scores and sex, disease severity, or comorbidities were found. Conclusion Quantitative smell testing demonstrates that decreased smell function, but not always anosmia, is a major marker for SARS‐CoV‐2 infection and suggests the possibility that smell testing may help, in some cases, to identify COVID‐19 patients in need of early treatment or quarantine.