Smell disorders at COVID-19-the current level of knowledge

Early reports of SARS-CoV-2 infections only rarely mentioned smell and taste disorders. Several studies, particularly from Europe and the USA, have now confirmed these symptoms as an early key feature of COVID-19. About 70 % of patients seem to experience a reduction of smell and taste in the course of the disease, with most of the studies published to date based on questionnaires and anamnestic data. Validated smell tests have so far only been used in a few studies. A distinction between taste and taste disorders, i.e. a distinction between retronasal aroma taste and the olfactory system from the dysfunction of taste capsules and the further cranial nerves, was mostly not made in the studies available to date. Some reports associate olfactory disorders with a milder clinical course. At the same time, the olfactory system via the olfactory bulb represents an entry point into the central nervous system, and an olfactory disorder could be a predisposing factor for central neurological symptoms. The clinical significance of smell and taste disorders in COVID-19 patients is currently still unclear. Further open questions concern the exact prevalence and the prognosis, so that overall higher quality studies with validated smell tests and larger numbers of patients are required.