A quick olfactory test showed promise as a COVID-19 screening tool in a pilot study.
The novel screen had a sensitivity of 75% and specificity of 95.2% in detecting COVID-19, compared with polymerase chain reaction (PCR) testing from nasopharyngeal swabs, reported Carol Yan, MD, of the University of California San Diego, and co-authors.
When fatigue as a COVID-19 symptom was included with olfactory test results, sensitivity rose to 93.8% and specificity was 89.8%, the team reported in a JAMA Otolaryngology-Head & Neck Surgery research letter.
Smell loss is one of the earliest and strongest predictors of SARS-CoV-2 infection, Yan and colleagues noted. "Compared with objective testing, subjective olfactory assessments significantly underreport olfactory dysfunction."
The study prospectively evaluated 163 participants at a college campus COVID-19 screening site using a novel scent card from SAFER Diagnostics followed immediately by SARS-CoV-2 PCR testing. The SAFER card contained a single scent in a scratch-and-sniff label that each participant identified from eight options: lemon, grape, floral, blueberry, banana, mint, unsure, or no scent.
The answers were processed by scanning a QR code, and an incorrect choice was classified as olfactory dysfunction. The researchers also collected data about demographics, medical history, COVID-19 symptoms, and subjective smell function. Most participants were men, and mean age was 25.
A total of 16 people were PCR-positive for COVID-19 and 75% of them failed the olfactory test. Of the 147 people testing PCR-negative for COVID-19, 4.8% failed the olfactory test.
Only 37.5% of PCR-positive participants reported subjective anosmia, even though 75% had failed the scent card test. Compared with other symptoms including cough, fever, fatigue, and history of COVID-19 exposure, a failed scent card screen was the greatest predictor of COVID-19 positivity (OR 80.24, 95% CI 14.77-435.90), albeit with a wide confidence interval.
The positive predictive value of the scent card in detecting people with COVID-19 was 63.2%; the negative predictive value was 97.2%.
Screening with a single scent may lower test sensitivity at the expense of expediency, Yan and co-authors observed. Not all patients with COVID-19 experience smell loss, and other common COVID-19 symptoms like fatigue can help increase sensitivity.
The pilot study was limited by its small sample size, small percentage of PCR-positive participants, and recruitment at a single college campus, the researchers acknowledged.
"Future studies with a larger sample size and a heterogeneous population may better account for other olfactory dysfunction risk factors and optimize sensitivity using a combination of olfactory testing with other symptoms for screening COVID-19," Yan and co-authors wrote.
Disclosures
This work was supported by SAFER Diagnostics.
One co-author is the founder of SAFER Diagnostics; no other disclosures were reported.
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