Latest discoveries related to taste and smell disorders in patients with post-COVID-19 and other neuroviruses – a systematic literature review

Introduction: The SARS CoV-2 infection, responsible for COVID-19, has spread worldwide start-ing with the end of 2019, with major impact in the years 2020 and 2021, especially through the alpha, beta, and delta strains respectively. These strains have also been associated with the de-velopment of symptoms of anosmia and ageusia, even after overcoming the acute form of the disease, as part of the post-COVID-19 sequalae that make up the so-called “long-Covid”. [1] The purpose of this systematic literature review was to study these disabling symptoms in the con-text of long-COVID syndrome. Material and methods: In order to accomplish this review, we used the method Preferred Re-porting Items for Systematic Reviews and Meta-Analyses (acronym - PRISMA) to filter and select the articles of interest that appeared in the period 1/01/2021-31/12/2022, in the international med-ical databases: Elsevier, NCBI/ PubMed,NCBI/ PMC and PEDro (= Physiotherapy Evidence Data-base classification), as well as ISI Web of Knowledge (Institute for Scientific Information - ex Thomson Reuters - Clarivate Analytics). We used the keywords for the selection: "COVID-19" / "viral neuroinfections" + "smell" /”olphactory” + "taste" /”gustatory”+ "anosmia" + 'ageusia' +'recovery'+'rehabilitation'. Results and discussion: After applying indirect and then direct quantitative and qualitative fil-tering, 25 articles remained that met the selection criteria (noted in order of relevance in table 1, at the end of the article). We also added a number of freely identified papers, considered relevant to our topic. We studied aspects of the "long-COVID" syndrome, mainly related to neu-ro-psychiatric symptoms - especially taste and smell disorders (anosmia/ageusia), risk factors, predictors for this status, pathophysiology, their intricate mechanism of action, frequency of symptoms, neuroanatomy imaging correlated with clinical aspects, effect of anosmia and ageu-sia on quality of life, recovery from such sequelae, favorable/unfavorable prognostic factors in this regard. Conclusions: Smell and taste are more than just simple sensations/perceptions and anosmia/ ageusia does not always recover spontaneously. The category of patients who are left with such permanent qualitative/quantitative alterations requires in-depth study in order to establish standardized and more effective methods of diagnosis, evaluation and treatment and recovery, than those available at the moment. The chosen topic represents a partially studied niche in the current well of knowledge, which will allow us, following the theoretical and practical deepen-ing of the subject, some possible elements of future contribution.