- Researchers from Europe think one of the most puzzling coronavirus symptoms might have an unexpected silver lining.
- The sudden loss of smell and taste is associated with a better COVID-19 prognosis, doctors from France and Belgium concluded.
- The scientists studied hundreds of COVID-19 patients, separating them into four groups depending on the severity of the illness. They said the loss of smell seems to be a good indicator of a milder course of COVID-19.
The clinical manifestations of COVID-19 make it difficult for physicians to diagnose the illness without a PCR test. Most early symptoms can be associated with the flu or a common cold, and that’s not the only problem. Some people infected with the novel coronavirus never experience any symptoms at all, and those who do won’t always report the same symptoms. There is one particular symptom that points to a coronavirus infection fairly reliably though, and that’s the sudden loss of smell (anosmia) and taste (ageusia). Doctors have already been trained to expect the symptoms and associate them with COVID-19 rather than other illnesses. Anosmia can appear with other medical conditions, so a regular PCR test would still be required to confirm the COVID-19 diagnosis.
As telling as the loss of smell might be, however, not everyone who gets COVID-19 will experience it. Several studies already explained why anosmia occurs, but there’s now an exciting development on the matter from Europe. Researchers think that the loss of smell can be used as a predictor for the prognosis of the illness. Specifically, anosmia might be an indication of a mild-to-moderate case of the disease.
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Researchers from the Foch de Suresnes hospital in France and Mons University in Belgium analyzed data from 1,300 COVID-19 patients, dividing the group into four types of COVID-19. The “light” group could be treated at home without any problems. The “moderates” showed some trouble breathing. The “severe” group included patients who required oxygen therapy in hospitals. The “very severe” group needed intensive care.
“The loss of smell is a factor of good prognosis, in the evolution of a COVID,” Dr. Jérôme Lechien told Le Parisien. The doctors found that only 10% to 15% of patients in groups 3 and 4 experienced loss of smell. Comparatively, 70% of patients in group 1 and 85% of patients in group 2 developed anosmia.
Previous studies have shown that the virus can infect cells in the olfactory region of the nose, and the resulting inflammation would then block the nerves from sensing smell. The symptom is transitory, and COVID-19 patients typically regain their sense of smell a few weeks after clearing the disease.
The researchers from France and Belgium can’t explain why anosmia indicates a better prognosis for COVID-19. The running hypothesis is that the symptom triggers a faster immune response, potentially preventing the virus from reaching the lungs and impacting blood vessels. Both of these organs see significant harm in severe COVID-19 cases.
“Our hypothesis is that the loss of smell means that the virus gets not only to the nose but also to the central nervous system,” Lechien said. “MRI images then show damage to the olfactory bulb, a region located at the base of the brain and which has a major role in smell. The virus is then contained by the immune system. This prevents it from having too much passage through the lungs and the blood, which is the case in the most serious cases.”
He continued, noting that the loss of smell would then trigger the loss of taste. “The ability of Covid-19 to invade the olfactory bulb and the central nervous system helps to explain the associated frequency of taste disorders.”
The researchers also said that 75% to 85% of patients who lose their sense of smell recover it within two months after the illness is cleared. Other studies said it could be even sooner. The sense of taste returns in 90% of cases. More good news concerns treatment with steroids, a class of drugs that proved effective against the virus in clinical trials — dexamethasone is one of them. These drugs can reduce the inflammation of the olfactory bulb, treating anosmia as a result.
As always with new COVID-19 studies, more research on the matter could further support these findings. But it’s important to note that anosmia will not guarantee a better COVID-19 prognosis. Some of the people in the study who experienced the symptom still went on to develop severe complications.