Background: In the context of Covid-19 infections, acute Olfactory Dysfunction (OD) is defined as decreased or altered sense of smell of duration of 14 days or less, in the absence of chronic rhinosinusitis, a history of head trauma, or neurotoxic medications. OD can be associated with flavor (smell+taste) dysfunction. However, Covid-19 may also affect real taste (sweet, salty, bitter, acidic, umami). OD is estimated to afflict 3%-20% of the population. Post-viral anosmia accounts for up to 40% of cases of anosmia or coronaviruses are thought to account for 10%-15% of these cases. As such, it is plausible that Covid-19 may cause OD. Aim: This work aims to determine the prevalence of olfactory dysfunction in coronavirus disease 2019 (Covid-19) patients. Materials & Methods: A systematic search was performed over different medical databases to identify sss studies, which studied the prevalence of olfactory dysfunction in Covid-19 patients. We conducted a meta-analysis process on the pooled prevalence of olfactory dysfunction as a primary main outcome. Results: Twelve studies were identified involving 16866 Covid-19 patients. Our meta-analysis process showed a pooled prevalence of olfactory dysfunction in Covid-19 patients=42.7% (95% CI=28.83 to 57.24) (p<0.001). Conclusion: To conclude, olfactory dysfunction is common in Covid-19 and maybe the only symptom. Coronavirus disease 2019-related OD can be severe and prolonged. Mucosal infiltration by CD68+ macrophages expressing SARS-CoV-2 viral antigen may contribute to Covid-19-related OD.
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