New Olfactory Dysfunction Test May Help Diagnose Mild COVID-19

By Marilynn Larkin

January 19, 2021

NEW YORK (Reuters Health) - A new rapid test, the Clinical Olfactory Dysfunction Assessment (CODA), uses paper strips and essential oils to help in the diagnosis of COVID-19, researchers say.

"Olfactory dysfunction is not anecdotal; our study confirms its high prevalence in COVID-19 (one out of three patients), and the follow-up shows a significant proportion of patients for whom recovery is late or incomplete - i.e., one out of four without full olfactory recovery at three months follow-up," Dr. Charles Villerabel of the University of Montpellier told Reuters Health by email.

"Our study confirms the strong specificity of the evaluation of olfactory dysfunction in the diagnosis of COVID 19, by the patient interview and by a psychophysical test," he said. "Our results suggest that patients suspected of having COVID 19 should, at a minimum, be questioned about their sense of smell as a first line of assessment."

As reported in JAMA Otolaryngology-Head and Neck Surgery, the prospective diagnostic study was conducted in a COVID-19 screening center at a university hospital in France from March 23 to April 22, 2020. Participants were 809 healthcare workers or outpatients with symptoms or with close contact with an index case. The mean age was 42 and close to two-thirds were women.

All participants underwent CODA assessment, in which participants identified and rated the intensity of three scents - lavender, lemongrass, and mint - to achieve a summed score ranging from 0 to 6 (lower score meant smells not recognized and/or lower intensities detected).

COVID-19 status was assessed using RT-PCR.

Fifty-eight patients (7.2%) tested positive for SARS-CoV-2. Chemosensory dysfunction was reported by 34.5% of those with COVID-19 versus 3.9% who tested negative.

Olfactory dysfunction, either self-reported or clinically ascertained (CODA score, 3 or less), yielded similar sensitivity (0.31 vs. 0.34) and specificity (0.97 vs. 0.98) for a COVID-19 diagnosis, with high concordance.

Fifteen of 19 participants (78.9%) with both reported olfactory dysfunction and a CODA score of 3 or less were confirmed to have COVID-19. The CODA score also revealed five participants (26.3%) with confirmed COVID-19 who had previously unperceived olfactory dysfunction.

However, 14 patients with a CODA score of 3 or less also tested negative for COVID-19.

Dr. Masha Niv, Vice Dean at the Hebrew University of Jerusalem's Faculty of Agriculture, Food and Environment and a member of the leadership team of The Global Consortium for Chemosensory Research, commented by email to Reuters Health. "Three different scents located on the extremity of paper strips previously dipped in 5 microL of essential oil seems very practical," she said. However, "As noted by authors, the specific scents may be need to be chosen according to the geographic region."

Further, she noted, "CODA enabled identification of five additional patients among those who did not report smell loss, but had low CODA scores. However, CODA also falsely predicted 14 patients, who had negative tests."

"Given the extra cost and complexity of administering the CODA test, and seeing that it has a rather high false positive rate when applied to patients who did not self-report smell loss, there is potential and promise in the CODA approach," she said, "but I think that further optimization of specificity is advisable."

"A more sensitive scale, using more scents, perhaps giving more weight to intensity rating over ability to recognize scents, and other tweaks to the procedure can be envisioned," she concluded.

Dr. Aria Jafari, an otolaryngologist at the University of Washington School of Medicine in Seattle, also commented by email. "A screening tool that has not yet been validated such as the CODA should be used with great caution," he said. "While the study demonstrated the value of using this tool in a context where there was relatively high prevalence of COVID-19 disease (screening facility), the extractor ability to the general population is less clear."

"Furthermore, we know that olfactory loss is relatively common within the general population and much more so with advanced age," he said. "For this reason, the utility of this as a screening tool, which would include a significant proportion of the population, is unclear, particularly as other symptoms such as cough and fever are much more suggestive, specific, and may be more temporally sensitive."

"It is known that olfactory loss can persist for several weeks after infection with COVID-19," he noted. "So, although one may have these symptoms, the temporal association with the infection and infectivity would not be able to be ascertained by the CODA test, limiting its utility."

SOURCE: JAMA Otolaryngology-Head and Neck Surgery, online January 7, 2021.