Olfactory disorders in COVID-19 patients as a prognostic factor: a systematic review

BACKGROUND: The reduction, loss, or impaired sense of smell and taste is common in patients with COVID-19. We aimed to investigate olfactory disorders (ODs) in patients with COVID-19 as a prognostic factor. METHODS: In this systematic review and meta-analysis, studies that assessed ODs in patients with COVID-19 were included. International databases, including PubMed, Embase, MEDLINE, Web of Science, and Scopus, were searched up to 20 March 2021. The random-effects model was used to combine the results of studies. Results were reported with a 95% confidence interval. RESULTS: In this study, out of 724 references, ten studies had the inclusion criteria. The odds of death in patients with the OD were 69% lower than in those without the ODs (OR = 0.31, 95% CI: 0.14, 0.69), and OD increased the odds of positive polymerase chain reaction (PCR) test (OR = 13.34, 95% CI: 4.2, 42.37). CONCLUSIONS: The findings of our study showed that OD had an inverse and significant relationship with death in COVID-19 patients, and the patients with OD seemed to have a lower risk of mortality.