Loss of smell and taste: Distinguishing between COVID-19 and the common cold/flu

The temporary loss of taste and smell are some of the earliest indicators of COVID-19.

Temporary loss of smell (anosmia), and taste (ageusia) are two symptoms that can differentiate COVID-19 from the common cold and flu, according to a new statement by the US Surgeon General Jerome Adams, MD, MPH. These two symptoms are also some of the earliest and most commonly reported indicators of COVID-19 and may better predict positivity compared with other symptoms such as fever and cough.

COVID-19 patients are 27 times more likely to experience the loss of smell, but only around 2.2 to 2.6 times more likely to have fever, cough, or respiratory difficulty, compared to those without COVID-19. An average of 47% (up to 80%) of people who test positive for COVID-19 can have subjective complaints of smell or taste loss. That percentage rises when these patients are tested using objective methods that measure the function of smell. Most patients first notice problems with their sense of smell; however, because smell is necessary to taste flavor, the symptoms are often connected.

According to one Italian report, out of 187 patients having a mild form of COVID-19 and not requiring hospitalization, 113 reported an alteration when asked to rate their sense of smell or taste. One month after initial positive diagnosis, 55 patients reported full recovery of taste and smell, 46 reported symptom improvement, and 12 reported no change or worsening of symptoms.

Another retrospective study showed that COVID-19 patients with normal smell function appeared to have a worse course of disease and were more likely to be hospitalized and placed on a ventilator. This suggests that patients who experience smell dysfunction may have a milder form of COVID-19 or for the most part be asymptomatic. The data also suggests that in a substantial percentage of the COVID-19–infected population, smell loss can be one of the first, or only, signs of disease which can be important to recognize in a largely asymptomatic younger population.

Although the exact mechanism behind the virus’ effect on smell and taste is elusive, one study suggests that the novel coronavirus changes the sense of smell/taste in patients not by directly infecting neurons but by affecting the function of supporting cells. Temporary loss of function of supporting cells in the olfactory epithelium, which indirectly causes changes to olfactory sensory neurons, results in symptomatic changes. According to lead author Sandeep Robert Datta, MD, PhD, “I think it’s good news, because once the infection clears, neurons don’t appear to need to be replaced or rebuilt from scratch,” which can take a longer period of time.

*from Perio-Implant Advisory, author: Scott Froum, DDS