COVID and loss of taste

This morning I woke up with a pretty strong sore throat. I took some throat lozenges and while it is is not necessarily sore, I have a strange sensation in my throat and my sense of taste is a bit impaired. My girlfriend and I had plans for tonight, so I texted her explaining that I had this throat issue (but still tested negative for COVID). I also explained that I heard that loss of taste is not a common symptom of COVID anymore so I thought I didn’t have COVID.

But…this is what I heard through friends. I wanted to see for myself what the evidence was. Some searching turns up a May 2022 article in a medical jorunal first-authored by Daniel Coelho. Coelho used a database consisting of 3.7 million COVID+ patients (the “National COVID Cohort Collaborative” or “N3C” database). The authors did a very simple tabulation of COVID strain and whether or not the patient was formally diagnosed with smell/taste disturbance.

One thing that struck me about this table is that smell/taste disturbance makes up quite a small fraction of COVID patients, and it always has. Only 1.3 percent of COVID patients from the initial wave were formally diagnosed with smell/taste loss, and this has only gone down with recent variances, to less than one percent of people with the Alpha, Delta, and Omicron variants.

My one question about this is how was smell/taste disturbance measured and to do that I would have to know more about the N3C data. Apparently a medical practitioner would have to make this determination (which I am guessing is based on asking the patient), but do we know if this means the patient ever had smell/taste disturbance or only if they had it at the time they were seeking medical treatment? Are the practitioners asking all 3.7 million patients if they have smell/taste disturbance or is that recorded only if the patient volunteers that information? Or, are doctors even bothering to officially record this diagnosis even if they know the symptoms exist, since it is a relatively benign symptom and they have bigger fish to fry, namely, a potentially lethal case of COVID?

Another point is that my assurance to my girlfriend that I probably did not have COVID because smell/taste loss is becoming less of a symptom of COVID was falling prey to a common numeracy error I caution my students again. Smell/taste disturbance may be an uncommon symptom of COVID (e.g. the proportion of COVID cases with smell/taste disturbance is small) but COVID may be common among people with smell/taste disturbance (the proportion of smell/taste disturbance cases with COVID is high). In fact, Coelho did say that this is the case when he was interviewed by the PR person at Virginia Commonwealth University: “Loss of smell and taste is still a good indicate of a COVID-19 infection…” Of course, to speak authoritatively to this, one would have to have data on cases of people with smell/taste disturbance and calculate the fraction of COVID cases, but I assume Coelho is using his medical expertise to say that smell/taste disturbance is very uncommon outside of the COVID context.