DATA SOURCES: PubMed, Scopus, Web of Science, Embase, and Google Scholar databases were searched to identify studies published between December 1, 2019, and June 23, 2020, without language restrictions. There was no restriction on the study design; therefore, observational studies, clinical trials, and case series were included. In addition, preprints were considered if data of interest were reported.

REVIEW METHODS: Two authors independently screened articles for eligibility. A random effects model was used to estimate the pooled prevalence with 95% CIs. Quality assessment was done with critical appraisal tools of the Joanna Briggs Institute. The robustness of the pooled estimates was checked by subgroup and sensitivity analyses.

RESULTS: Fifty-nine studies were included (N = 29,349 patients, 64.4% female). The pooled prevalence of taste disorders in patients with COVID-19 was 48.1% (95% CI, 41.3%-54.8%). The prevalence of taste disorders in studies with objective assessments was higher as compared with subjective assessments (59.2% vs 47.3%). The disorders were observed in 55.2% of European patients; 61.0%, North American; 27.1%, Asian; 29.5%, South American; and 25.0%, Australian. Ageusia, hypogeusia, and dysgeusia were detected in 28.0%, 33.5%, and 41.3% of patients with COVID-19. We identified 91.5% of the included studies as high quality.

METHODS: We searched the PubMed and Google Scholar on 15th May 2020, with search terms including SARS-COV-2, coronavirus, COVID-19, hyposmia, anosmia, ageusia and dysgeusia. The articles included were cross sectional studies, observational studies and retrospective or prospective audits, letters to editor and short communications that included a study of a cohort of patients. Case reports, case-series and interventional studies were excluded.

DISCUSSION: A total of 16 studies were selected. Incidence of smell and taste dysfunction was higher in Europe (34 to 86%), North America (19 to 71%) and the Middle East (36 to 98%) when compared to the Asian cohorts (11 to 15%) in COVID-19 positive patients. Incidence of smell and taste dysfunction in COVID-19 negative patients was low in comparison (12 to 27%). Total incidence of smell and taste dysfunction from COVID-19 positive and negative patients from seven studies was 20% and 10% respectively. Symptoms may appear just before, concomitantly, or immediately after the onset of the usual symptoms. Occurs predominantly in females. When occurring immediately after the onset of the usual symptoms, the median time of onset was 3.3 to 4.4 days. Symptoms persist for a period of seven to 14 days. Patients with smell and taste dysfunction were reported to have a six to ten-fold odds of having COVID-19.