The importance of olfactory and gustatory disorders as early symptoms of coronavirus disease (COVID-19).

Sir,

Early detection and isolation of pauci-symptomatic patients with coronavirus disease 19 (COVID-19) is proving to be a key factor in the fight against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

The first European case series are reporting a high frequency of olfactory and gustatory dysfunctions in COVID-19 patients.1, 2, 3 However, all these studies are anamnestic, without any objective sensitive evaluation of the patients.

Based on this evidence, we recently proposed an objective functional chemosensitive evaluation protocol for these patients. With this methodology we are bringing to a conclusion a vast Italian multicentre study on more than 300 patients. The first results seem to be very important and can be useful to alert the scientific community to the importance of chemosensitive disorders in early COVID-19.

First, chemosensitive disorders are common in the course of infection, affecting about 80% of our case studies. Moreover, these symptoms are typical of the early stages of the disease, generally occurring two days after the onset of the fever. In 15.3% of patients, temporary taste and / or smell disturbances were the only manifestation of COVID-19. Secondly, the reduction of taste and smell spontaneously regressed in a few days in 67.5% of cases. However, on functional tests, these patients had an increase in the sensory threshold when the discriminative ability was fully recovered. Thirdly, there appears to be a statistically significant correlation between the duration of the chemosensitive disorder and the severity of the disease. In patients in whom the alteration of taste and smell lasts more than 10 days, the risk of developing a severe pulmonary clinical picture was 2.4 times greater. These preliminary results could have important pathogenetic and clinical implications. The detection of sudden chemosensitive dysfunction, typically not associated with nasal obstruction or rhinitis symptoms, is highly suspicious of an ongoing COVID-19 infection. The tendency to spontaneous regression of these disorders, associated with the relative frequency of manifestations related to an involvement of the central nervous system, could suggest that the virus has non-neuronal targets rather than a pathogenesis linked to neuronal death induced in the olfactory bulb. Prospective follow-up of these patients and histopathological analysis of samples from patients who have died from COVID-19 will help us better understand the pathogenetic mechanisms that underlie these disorders. Finally, the correlation between the duration of chemosensitive disorders and the severity of the disease would suggest that there may be a relationship between the persistence of viral multiplication in the upper airways and the severity of the disease. However, to confirm this hypothesis, studies will be needed to correlate the symptomatic picture to the viral load in seriate rhino-pharyngeal swabs.

Conflict of interest

We have no conflicts of interest.

Ethics statement/confirmation of patient permission

Not applicable.