Rapid Olfactory Test Shows Potential as Screening Tool for COVID-19

A study that evaluated the feasibility of a novel, objective olfactory test as part of an initial screening for COVID-19 in adults with unknown disease status has concluded that olfactory dysfunction (OD) is one of the earliest and strongest predictors of COVID-19 infection, and thus is promising as a disease screening tool.

In the prospective, cross-sectional study, researchers at University of California, San Diego (La Jolla, CA, USA) enrolled healthy adults (aged ≥ 18 years) from a single college campus COVID-19 screening site. Participants were screened for OD using a novel scent card (SAFER Diagnostics) followed immediately by polymerase chain reaction (PCR) testing for SARS-CoV-2 from nasopharyngeal swabs. The SAFER card contained a single scent in a scratch-and-sniff label that the participant identified from 8 answer options: lemon, grape, floral, blueberry, banana, mint, unsure, or no scent. Answers were processed electronically via a QR code. An incorrect choice was classified as OD. Participant demographics, medical history, COVID-19 symptoms, and subjective smell function on a binary and 10-point visual analog scale (VAS, with 0 indicating no sense of smell and 10 indicating normal sense of smell) were also collected.

A total of 163 participants were prospectively screened for OD using the scent card followed by SARS-CoV-2 PCR testing. Of those who tested PCR-positive for COVID-19, 75% (12 out of 16) failed olfactory screening compared with 4.8% (7 out of 147) among those testing PCR-negative for COVID-19. The sensitivity, specificity, positive predictive value, and negative predictive value of the scent card in detecting those with COVID-19 were 75.0%, 95.2%, 63.2%, and 97.2%, respectively. Including the symptom fatigue along with OD achieved 93.8% sensitivity and 89.8% specificity in disease screening. The addition of fever and cough did not further increase sensitivity.

While only 37.5% (6 out of 16) of COVID-19 test-positive participants reported subjective anosmia, 75% failed screening with the scent card. A failed scent card screen was the greatest predictor of COVID-19 positivity (odds ratio [OR], 80.24; 95% CI, 14.77-435.90) when compared with other symptoms including cough, fever, fatigue, and a history of COVID-19 exposure. Thus, the study demonstrated that a rapid psychophysical olfaction test is feasible as a screening tool for COVID-19.

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University of California, San Diego