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More than 50% of healthcare workers infected with SARS-CoV-2 report that their sense of smell has not returned to normal an average of 5 months post infection, new research shows.
The findings illustrate that olfactory problems are common not only during the acute COVID phase but also "in the long run" and that these problems should be "taken into consideration" when following up these patients, study investigator Johannes Frasnelli, MD, professor, Department of Anatomy, University of Quebec at Trois-Rivieres, Quebec, Canada, told Medscape Medical News.
Loss of sense of smell can affect quality of life because it affects eating and drinking, and may even be dangerous, said Frasnelli. "If your sense of smell is impaired, you may unknowingly eat spoiled food, or you may not smell smoke or gas in your home," he said.
In addition, Frasnelli noted that an impaired sense of smell is associated with higher rates of depression.
The findings will be presented at the American Academy of Neurology (AAN) 2021 Annual Meeting in April.
Research shows that about 60% of patients with COVID lose their sense of smell to some degree during the acute phase of the disease. "But we wanted to go further and look at the longer-term effects of loss of smell and taste," said Frasnelli.
The analysis included 813 healthcare workers in the province of Quebec. For all the patients, SARS-CoV-2 infection was confirmed through testing with a nasopharyngeal viral swab.
Participants completed a 64-item online questionnaire that asked about three senses: olfactory; gustatory, which includes tastes such as sweet, sour, bitter, salty, savory, and umami; and trigeminal, which includes sensations such as spiciness of hot peppers and "coolness" of mint.
They were asked to rate these on a scale of 0 (no perception) to 10 (very strong perception) before the infection, during the infection, and currently. They were also asked about other symptoms, including fatigue.
Most respondents had been infected in the first wave of the virus in March and April 2020 and responded to the questionnaire an average of 5 months later.
The vast majority of respondents (84.1%) were women, which Frasnelli said was not surprising because women predominate in the healthcare field.
The analysis showed that average smell ratings were 8.98 before infection, 2.85 during the acute phase, and 7.41 when respondents answered the questionnaire. The sense of taste was less affected and recovered faster than the sense of smell. Results for taste were 9.20 before infection, 3.59 during the acute phase, and 8.05 after COVID.
Among 580 respondents who indicated a compromised sense of smell during the acute phase, the average smell rating when answering the questionnaire was 6.89, compared to 9.03 before the infection. More than half (51.2%) reported not regaining full olfactory function.
The fact that the sense of smell had not returned to normal for half the participants so long after being infected is "novel and quite striking," said Frasnelli.
However, he noted, this doesn't necessarily mean all those with a compromised sense of smell "have huge problems." In some cases, he said, the problem "is more subtle."
Not a CNS Problem?
Respondents also completed a chemosensory dysfunction home test (CD-HT). They were asked to prepare common household food items, such as peanut butter, sugar, salt, and vinegar, in a particular way ― for example, to add sugar or salt to water ― and provide feedback on how these smell and taste.
For this CD-HT analysis, 18.4% of respondents reported having persistent loss of smell. This, Frasnelli said, adds to evidence from self-reported responses and suggests that in some cases, the problem is more than senses not returning to normal.
"From the questionnaires, roughly 50% said their sense of smell is still not back to normal, and when we look at the CD home test, we see that almost 20% of subjects indeed have pretty strong impairment of their sense of smell," he said.
The results showed no sex differences, although Frasnelli noted that most of the sample were women. "It's tricky to look at the data with regard to sex because it's a bit skewed," he said.
Male respondents were older than female participants, but there was no difference in impairment between age groups. Frasnelli said this was "quite interesting," inasmuch as older people usually lose some sense of smell.
The researchers have not yet examined whether the results differ by type of healthcare worker.
They have also not examined in detail whether infection severity affects the risk for extended olfactory impairment. Although some research suggests that the problem with smell is more common in less severe cases, Frasnelli noted this could be because loss of smell is not a huge problem for patients battling grave health problems.
As for other symptoms, many respondents reported lingering fatigue; some reported debilitating fatigue, said Frasnelli. However, he cautioned that this is difficult to interpret, because the participants were healthcare workers, many of whom returned to work during the pandemic and perhaps had not fully rested.
He also noted that he and his colleagues have not "made the link" between impaired smell and the degree of fatigue.
The COVID virus appears to attack supporting sustentacular cells in the olfactory epithelium, not nerve cells.
"Right now, it seems that the smell problem is not a central nervous system problem but a peripheral problem," said Frasnelli. "But we don't know for sure; it may be that the virus somehow gets into the brain and some symptoms are caused by the effects of the infection on the brain."
The researchers will extend their research with another questionnaire to assess senses 10 to 12 months after COVID.
Limitations of the study include the subjective nature of the smell and taste ratings and the single time point at which data were collected.
Commenting on the research for Medscape Medical News, Thomas Hummel, MD, professor, Smell and Taste Clinic, Department of Otorhinolaryngology, Technische Universität Dresden, Dresden, Germany, said the new results regarding loss of smell after COVID are "very congruent" with what he and his colleagues have observed.
Research shows that up to 1 in 5 of those infected with SARS-CoV-2 experience olfactory loss. "While the numbers may vary a bit from study to study or lab to lab, I think 5% to 20% of post-COVID patients exhibit long-term olfactory loss," Hummel said.
His group has observed that "many more are not back to normal," which conforms with what Frasnelli's study reveals, said Hummel.
Also commenting for Medscape Medical News, Kenneth L. Tyler, MD, professor of neurology, University of Colorado School of Medicine, Denver, Colorado, and a fellow of the American Academy of Neurology, said the study was relatively large and the results "interesting."
Although it "provides more evidence there's a subset of patients with symptoms even well past the acute phase" of COVID, the results are "mostly confirmatory" and include "nothing super surprising," said Tyler.
However, the investigators did attempt to make the study "a little more quantitative" and "to confirm the self-reporting with their validated CD home test," he said.
Tyler wondered how representative the sample was and whether the study drew more participants with impaired senses. "If I had a loss of smell or taste, maybe I would be more likely to respond to such a survey," he said.
He also noted the difficulty of separating loss of smell from loss of taste.
"If you lose your sense of smell, things don't taste right, so it can be confounding as to how to separate out those two," he noted.
The study was supported by the Foundation of the University of Quebec at Trois-Rivieres and the Province of Quebec. Frasnelli has received royalties from Styriabooks in Austria for a book on olfaction published in 2019 and has received honoraria for speaking engagements. Hummel and Tyler have disclosed no relevant financial relationships.
American Academy of Neurology (AAN) 2021 Annual Meeting: Abstract 2192. To be presented April 20, 2021.
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Cite this: Loss of Smell Lingers Post COVID - Medscape - Feb 23, 2021.