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

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. Metaanalysis 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.

The usefulness of a quantitative olfactory test for the detection of COVID-19

“…Our results showed that the olfactory test specificity to detect OD in patients infected with COVID-19 was very high (∼95%), which is consistent with other reports 23 including by the CDC 24 indicating that “a new loss of taste or smell” is the single best indicator symptom of COVID-19, as based on the odds ratio. Although OD is acknowledged by many research teams and listed on the WHO website as a finding consistent with SARS-CoV-2 infection, little attention is given that OD is a better indicator of COVID-19 than other symptoms.…”

Population-based seroprevalence of SARS-CoV-2 antibodies in a high-altitude setting in Peru

“…Our results are consistent regarding some factors associated with a greater probability of positivity to COVID-19, for example, the symptoms described such as anosmia or respiratory distress, in the context of the pandemic, have a strong disease predictive association. 25 In recent systematic reviews and meta-analyses, anosmia has been similarly associated with COVID-19 infection with an OR between 11 and 14, 26,27 like in our study. These findings could be overestimated as the prevalence of our outcome was high (> 20%), but when correcting the analyzes using Prevalence Ratios (PR) for smell/taste alteration, the PR was 2·74 (2·41-3·12), a significant association but with lower point estimates.…”

Loss of Smell and Taste Can Accurately Predict COVID-19 Infection: A Machine-Learning Approach

“…Although SARS-Cov-2 accesses the respiratory system with most people experiencing a mild or subclinical disease, especially in the early stages, clinical manifestations of COVID-19 are broad and include common symptoms such as malaise, fever, cough, shortness of breath, myalgia, sore throat, headache, nausea, or diarrhea [ 1 , 2 ]. Nevertheless, loss of smell and taste have emerged as the most prevalent and predictive symptoms in mild COVID-19 cases [ 3 , 4 ].…”