Olfactory & taste dysfunction in COVID-19 patients: Pathogenesis and associated factors

Introduction: Olfactory and taste dysfunction (OTD) have been widely reported as a key symptoms in Covid-19 patients. It also can be manifested as an isolated symptom that caused delay in diagnosis of SARS-CoV2 infection. Identifying the mechanism of OTD and its associated factors may help to understand its association with Covid-19 manifestation. Methods: Literature search was conducted via database PubMed, Scopus, Embase and Science Direct using keyword (anosmia OR olfactory dysfunction) AND (ageusia OR taste dysfunction) AND (pathogenesis) AND (associated factor) AND (Covid-19 or SARS CoV-2). About 93 abstracts related to the keywords were retrieved. Only 54 articles which fulfilled the criteria such as published in English, available full text and peer-review or data based research have been selected. Results: Prevalence of OTD in Covid-19 patients varies markedly between studies from 5.1% to 98.0%. Duration of anosmia ranging from 4 to 28 days and appeared as early as day 1 post infection. Some authors postulated that OTD occurs due to angiotensin converting enzyme 2 (ACE2) assisted the coronavirus to stimulate neuronal damage. Besides, viruses also can directly damage the olfactory epithelium, nerve and central pathway. Most studies which looked at the association between OTD with olfactory damage using computed tomography scan and magnetic resonance imaging showed insignificant findings. There were studies that showed that OTD related with gender and age. High proportion of OTD in COVID-19 cases were female, young patients, non-smoker, patients without comorbid and in mild to moderate symptoms of COVID-19. There were limited and inconsistent results for the relationship between viral load and OTD. However, there was no relation between previous neurological disorder with OTD. Conclusion: The pathogenesis of OTD in Covid-19 and its association between viral load with its severity of OTD is still debatable and further study is warranted. The researchers need to look at all perspectives, allowing sufficient data to be explored to get more understanding about OTD in COVID-19.