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Meta-Analysis
. 2020 Oct 13;20(12):76.
doi: 10.1007/s11882-020-00972-y.

Frequency and Clinical Utility of Olfactory Dysfunction in COVID-19: a Systematic Review and Meta-analysis

Khang Wen Pang  1 , Jeremy Chee  2 , Somasundaram Subramaniam  3 , Chew Lip Ng  3
Affiliations
Meta-Analysis

Frequency and Clinical Utility of Olfactory Dysfunction in COVID-19: a Systematic Review and Meta-analysis

Khang Wen Pang et al. Curr Allergy Asthma Rep. .

Abstract

Background: Olfactory dysfunction (OD) has been gaining recognition as a symptom of COVID-19, but its clinical utility has not been well defined.

Objectives: To quantify the clinical utility of identifying OD in the diagnosis of COVID-19 and determine an estimate of the frequency of OD amongst these patients.

Methods: PubMed was searched up to 1 August 2020. Meta-analysis A included studies if they compared the frequency of OD in COVID-19 positive patients (proven by reverse transcription polymerase chain reaction) to COVID-19 negative controls. Meta-analysis B included studies if they described the frequency of OD in COVID-19 positive patients and if OD symptoms were explicitly asked in questionnaires or interviews or if smell tests were performed.

Results: The pooled frequency of OD in COVID-19 positive patients (17,401 patients, 60 studies) was 0.56 (0.47-0.64) but differs between detection via smell testing (0.76 [0.51-0.91]) and survey/questionnaire report (0.53 [0.45-0.62]), although not reaching statistical significance (p = 0.089). Patients with reported OD were more likely to test positive for COVID-19 (diagnostic odds ratio 11.5 [8.01-16.5], sensitivity 0.48 (0.40 to 0.56), specificity 0.93 (0.90 to 0.96), positive likelihood ratio 6.10 (4.47-8.32) and negative likelihood ratio 0.58 (0.52-0.64)). There was significant heterogeneity amongst studies with possible publication bias.

Conclusion: Frequency of OD in COVID-19 differs greatly across studies. Nevertheless, patients with reported OD were significantly more likely to test positive for COVID-19. Patient-reported OD is a highly specific symptom of COVID-19 which should be included as part of the pre-test screening of suspect patients.

Keywords: COVID-19; Coronavirus 2; Meta-analysis; Olfaction disorders; Severe acute respiratory syndrome.

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Conflict of interest statement

The authors declare no conflicts of interest relevant to this manuscript.

Figures

Fig. 1
Fig. 1
Flow diagram for meta-analysis A showing the clinical significance of OD in the diagnosis of COVID-19. aFifty-seven full-text articles were excluded: 49 did not include controls, 4 utilised inappropriate controls who were not swabbed for COVID-19 (3 studies used healthy asymptomatic individuals as controls and 1 study used historical influenza patients as controls), 2 utilised self-reported COVID testing results, 1 added in OD symptoms to their data collection sheet midway through the study and 1 did not explicitly ask for OD symptoms
Fig. 2
Fig. 2
Meta-analysis A showing the clinical significance OD in the diagnosis of COVID-19. a Diagnostic odds ratio. b Pooled sensitivity. c Pooled specificity of OD in predicting COVID-19 infection
Fig. 3
Fig. 3
Flow diagram for meta-analysis B estimating the frequency of OD amongst COVID-19 patients. aSixteen full-text articles were excluded: 9 did not specify if OD symptoms were explicitly asked, 5 likely used overlapping data and 2 utilised self-reported COVID testing results
Fig. 4
Fig. 4
Meta-analysis B estimating the frequency of OD amongst COVID-19 patients. Pooled prevalence of olfactory dysfunction (OD) amongst COVID-19 patients with subgroup analysis by OD testing method
Fig. 5
Fig. 5
Funnel plots for a meta-analysis A showing the clinical significance OD in the diagnosis of COVID-19 and b meta-analysis B estimating the frequency of OD amongst COVID-19 patients
See this image and copyright information in PMC

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