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. 2021 Dec 7;9(4):E1134-E1140.
doi: 10.9778/cmajo.20210085. Print 2021 Oct-Dec.

Association between new-onset anosmia and positive SARS-CoV-2 tests among people accessing outpatient testing in Toronto, Ontario: a retrospective cross-sectional study

Braden O'Neill  1 , Sumeet Kalia  2 , Peter Gill  2 , Susan Hum  2 , Carla Moran-Venegas  2 , Rebecca Stoller  2 , Michelle Greiver  2 , Payal Agarwal  2 , Abirami Kirubarajan  2 , Samuel DeKoven  2 , David Eisen  2 , Andrew Pinto  2 , Sheila Dunn  2
Affiliations

Association between new-onset anosmia and positive SARS-CoV-2 tests among people accessing outpatient testing in Toronto, Ontario: a retrospective cross-sectional study

Braden O'Neill et al. CMAJ Open. .

Abstract

Background: Reports have suggested that anosmia is strongly associated with SARS-CoV-2 infection, but patients were often asked about this symptom after their diagnosis. This study assessed associations between prospectively reported anosmia and other symptoms related to SARS-CoV-2 infection, and SARS-CoV-2 positivity in community testing centres in Toronto, Ontario.

Methods: We conducted a retrospective cross-sectional study in which data were collected from 2 COVID-19 assessment centres affiliated with 2 hospitals in Toronto, Ontario, from Apr. 5 to Sept. 30, 2020. We included symptomatic profiles of all people who underwent a SARS-CoV-2 test at either clinic within the study period. We used generalized estimating equations to account for repeat visits and to assess associations between anosmia and other symptoms and SARS-CoV-2 positivity.

Results: A total of 83 443 SARS-CoV-2 tests were conducted across the 2 sites for 72 692 participants during the study period. Of all tests, 1640 (2.0%) were positive; 837 (51.0%) of people who tested positive were asymptomatic. The adjusted odds ratio for the association between anosmia and test positivity was 5.29 (95% confidence interval [CI] 4.50-6.22), with sensitivity of 0.138 (95% CI 0.121-0.154), specificity of 0.980 (95% CI 0.979-0.981), a positive predictive value of 0.120 (95% CI 0.106-0.135) and a negative predictive value of 0.983 (95% CI 0.982-0.984).

Interpretation: Anosmia had high specificity and a positive predictive value of 12% for SARS-CoV-2 infection in this community population with low prevalence of SARS-CoV-2 positivity. The presence of anosmia should increase clinical suspicion of SARS-CoV-2 infection, and our findings suggest that people presenting with this symptom should be tested.

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Conflict of interest statement

Competing interests: Rebecca Stoller declares a stipend as medical lead for the North York General Hospital COVID-19 assessment centre. Michelle Greiver reports a grant to her department from Sanofi, GlaxoSmithKline and Novartis for the development of a severe asthma registry using electronic medical record data. Michelle Greiver is director of UTOPIAN (University of Toronto Practice-Based Research Network) and lead of POPLAR (Primary care Ontario Practice-based Learning and Research Network). No other competing interests were declared.

Figures

Figure 1:
Figure 1:
Diagnostic measures of COVID-19 symptoms recorded at North York General Hospital and Women’s College Hospital (point estimates in blue, 95% confidence intervals in red). Note: LR = likelihood ratio, NPV = negative predictive value, PPV = positive predictive value. Abdominal pain
Figure 2:
Figure 2:
Diagnostic measures of COVID-19 symptoms recorded at Women’s College Hospital (point estimates in blue, 95% confidence intervals in red). Note: LR = likelihood ratio, NPV = negative predictive value, PPV = positive predictive value.
Figure 3:
Figure 3:
Odds ratios (ORs) for positive SARS-CoV-2 swab test, by patient characteristic (95% confidence intervals in red, dotted line shows OR = 1; results adjusted for age, sex, travel history and common symptoms available at both study sites: anosmia, cough and/or shortness of breath, diarrhea and/or abdominal pain).
See this image and copyright information in PMC

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