Regional and chronological differences in prevalences of olfactory and gustatory dysfunction in coronavirus disease (COVID-19): a systemic review and meta-analysis

Abstract Olfactory and gustatory dysfunction are frequently reported in patients with coronavirus disease (COVID-19). However, the reported prevalence of olfactory and/or gustatory dysfunction varies widely, and the reason for the inter-study differences is unclear. Hence, in this meta-analysis, we performed subgroup analyses to investigate the factors that contribute to the inter-study variability in the prevalence of olfactory and gustatory dysfunction. Out of 943 citations, we included 55 eligible studies with 13,527 patients with COVID-19 for a systematic review. The overall pooled prevalences of olfactory and gustatory dysfunction were 51.4% and 47.5%, respectively, in the random-effect model. In subgroup analyses, the prevalences of olfactory and gustatory dysfunction were significantly different among four geographical regions (both P < 0.001, respectively). Although the prevalences of olfactory and gustatory dysfunction did not significantly differ according to the time of enrollment, the subgroup analyses including only studies from the same geographical region (Europe) revealed a significant difference in olfactory dysfunction according to the time of enrollment. The regional and chronological differences in the prevalences of olfactory and gustatory dysfunctions partly explain the wide inter-study variability.