The Prevalence of Olfactory Dysfunction in the General Population: A Systematic Review and Meta-analysis.

Background: Olfactory dysfunction (OD) is common and has been reported as an early indicator of COVID-19. However, the reported prevalence of OD in the general population varies widely depending upon the metric used to assess olfaction. To perform a systematic review and meta-analysis of the prevalence of OD in the healthy general population, review the various assessment metrics used, and compare pooled OD prevalence rates.

Results: A total of 175,073 subjects were identified (mean age 63.5 years, range 18 to 101) with an overall OD prevalence of 22.2% (95% CI 14.8-30.6). OD prevalence was significantly greater using objective olfactory assessments, compared to subjective measures (28.8%, CI 20.3-38.2 versus 9.5%, CI 6.1-13.5, p < 0.001). The prevalence of OD was greater using expanded identification tests (>8 items) compared to brief test with ≤8 items (30.3%, CI 16.2-46.5 versus 21.2%, CI 12.3-31.8). Prevalence was higher in studies with a mean age greater than 55 years compared to those with a mean age of 55 years or less (34.5%, CI 23.4-46.5 versus 7.5%, CI 2.6-14.5, p < 0.001).

Conclusions: The reported prevalence of OD in the general population depends on the testing method and population age. OD prevalence was greater in studies using objective tests, expanded identification tests, and in those with older subjects.