Covid-19 and the Loss of Smell

In a little more than half of people infected with COVID-19, the sense of smell is compromised. Compared to people with other respiratory issues, those who test positive for COVID-19 are 27 times more likely to have smell loss while being only 2.2 to 2.6 times more likely to have fever, cough or respiratory difficulty. According to a report from the Harvard Medical School, SARS-CoV-2 does not directly infect olfactory neurons but may instead interfere with brain function by affecting vascular cells in the nervous system. The hypothesis hasn’t been verified, but given that most COVID-19 positive patients regain their sense of smell within 8 weeks, it suggests that nerve cells themselves aren’t damaged.

Two weeks ago my wife and I started experiencing mild symptoms: congestion, slight cough, and a fever that was gone within 36 hours. Our autistic son who often takes off his mask had been asking for his salbutamol inhaler a few days earlier. A couple of days after our symptoms surfaced ( Wednesday and Thursday) we all tested positive for COVID-19. But my wife and I only lost our sense of smell 5 days after the appearance of other symptoms.

I had tested my sense of smell using a jar of oregano. Each morning, for each of us, the smell seemed to get a little fainter until Monday March 15 (see graphic), when it totally disappeared. When its volatiles failed to excite our olfactory receptors that morning, it was then that we noticed that we were not smelling coffee, apples, tomato sauce, almond oil, nasal rub, eau de toilette, compost or any of the usual bathroom stenches. The next morning we also tested our ability to smell vanilla, peppermint, and lemon extract. Anosmia had kicked in.

This persisted until Friday. On that day there was faint smell for each of the three extracts and for oregano, and even coffee grounds led to a very faint stimulus. This condition is called hyposmia. There was little change until one of us observed some improvements on the morning of Tuesday, 8 days after the onset of anosmia. Encouragingly, for me, oregano’s smell was more intense and so was that of the other three. Coffee’s smell was still weak, and those of apples and other fruits were still totally absent.

On Thursday, 10 days after the onset of anosmia, although there was no response from rubbing my fingers on oleander and bringing them to my nose, but that did not apply when I did the same thing with a plant of lemon thyme. There was a faint aroma. Similarly whereas in the previous week I had not been able to smell broth, after leaving the house for half an hour, upon reentering there was an olfactory response, but it smelled like a less complex mixture than it really was. Meanwhile on the same day, the lemon, vanilla and peppermints extracts all seemed stronger, and the same was true when I stuck my nose into the 250 ml oregano jar.

Rather than tediously continue with prose, I recorded the rest of the observations in the following table. Initially I was apprehensive, given that there’s no guarantee that the sense would come back unblemished. The sense of smell alerts us to dangers, strongly evokes distant memories, makes eating far more pleasurable, puts us in tune with nature and plays an underappreciated role in romance. Unlike hearing and vision which depend on waves, smell involves a direct interaction with matter. I was relieved when the sense started to function again and fascinated by the way different smells were restored at different rates. Oddly, except for the smell of tomato sauce, the last smells to come back were mostly unpleasant ones.

A daily log of how my sense of smell gradually became more functional. Most smells returned within a month, but oddly hyposmia persisted mostly for unpleasant smells for at least 4 more weeks.

A Greek study published in January 2021 in the Journal of Clinical Medicine, most of the 182 patients (88%) recovered their sense of smell by two months, confirming the findings of last year’s studies. MRIs have been conducted in other patients for those who have recovered and for those less fortunate. In the latter case, the olfactory bulb has been not only inflamed but damaged.

Does this imply that anosmia for such patients is permanent? Olfaction without apparent bulbs is seen in 0.6% of women, but not in men. Somehow part of the cortex compensates for the bulb’s absence. Whether this corrective measure can only happen soon after birth and not necessarily after COVID remains to be seen.

Postscript

As shown above, in keeping track of my sense of smell’s recovery, I exposed my nose to a variety of smells almost on a daily basis. Inadvertently I imposed upon myself a form of “smell training therapy” , an approach that is effective in helping patients recover from COVID19 smell loss. We’ve often encountered how self-reporting can introduce a bias in medical studies. Here there was an experimental component to the tracking itself, which could have artificially accelerated my recovery.

If you are familiar with BBC’s Crowd Science, this week’s episode covered COVID19 smell loss.

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