Incremental Benefit of Using a History of Sudden Loss of Taste (Ageusia) And/Or Smell (Anosmia) in Symptom Screening for COVID-19

Purpose

This note provides a summary of scientific evidence and jurisdictional experiences on the incremental benefit of using a history of sudden loss of taste (ageusia) and/or smell (anosmia) in symptom screening to help identify people who may have COVID-19 and need to take appropriate action.

*The full version of the Briefing Note including the Appendix can be accessed in the PDF file at the top of the page*

Key Findings

Most of the identified evidence identifies loss of taste and/or smell as a strong predictor of COVID-19 and speaks to the value of including them, alongside other symptoms, in screening tools. No evidence was identified that directly addresses the incremental benefit of screening for sudden loss of taste and/or smell and how best to operationalize this symptom with other types of symptom screening (e.g., by self screening prompted by signage or using a questionnaire).
Many Canadian provinces, Australia, New Zealand, Sweden, and UK have included ageusia/anosmia in COVID-19 screening symptoms.
Using a list of COVID-19-related symptoms as a screening tool can be used:
- For those at high risk for COVID-19 (e.g., travellers passing through air, land, and sea borders) and for the entire population (e.g., on entering schools, stores, and workplaces);
- Alongside other potential screening tools (e.g., temperature taking); and
- For operationalization in different ways (e.g., by self screening prompted by signage, self-screening using a questionnaire, or screening using a questionnaire administered by another person; by randomly selecting individuals for symptom screening or screening everyone; and by varying the frequency of and settings for symptom screening).
Appropriate follow-up actions for those with an elevated temperature can include self-isolating and seeking a diagnostic test, among others, however, such follow-up actions are not the focus of this briefing note.

Analysis for Ontario:

Symptom screening to date in Ontario initially focused on six symptoms, namely fever, cough, shortness of breath and/or difficulty breathing, headache, runny nose, and sore throat. The Ontario government’s self-assessment tool, like the one used by the Government of Canada, now includes a much longer list of symptoms.

This section below summarizes scientific evidence and international/Canadian jurisdictional experiences on the incremental benefit of using a history of sudden loss of taste (ageusia) and/or smell (anosmia) in symptom screening to help identify people who may have COVID-19 and need to take appropriate action. Additional details are provided for experiences from Canadian provinces and territories, for experiences from other countries and for abstracts for highly relevant documents in the Appendix.

Scientific Evidence

Identified evidence consistently identifies loss of taste and/or smell as a strong predictor of COVID-19.
- For example, one recent Canadian study found that patients who test positive for SARS-CoV-2 infection are much more likely to have impaired taste and smell than those who test negative for the infection.
None of the evidence documents directly address the incremental benefit of screening for sudden loss of taste and/or smell, but many speak to the value of including it alongside other symptoms.
None of the evidence documents directly address how best to operationalize this or other types of symptom screening (e.g., by self screening prompted by signage or using a questionnaire).

International Scan

Loss of smell and taste is variably included in the self-assessments and other symptom lists across the countries that were examined:
- China, a country that was hit earlier by the effects of COVID-19, has not included ageusia/anosmia as a screening symptom.
- Countries that continue to develop their responses to the pandemic (i.e., Australia, New Zealand, and Sweden) have adapted screening tools to include this symptom.
- On May 18, 2020, the UK issued an updated statement on COVID-19 symptoms, advising that all individuals should self-isolate if they develop a new continuous cough, or fever, or anosmia.
- No information could be found about South Korea’s inclusion loss of taste and smell in their list of screening symptoms.

Canadian Scan

The Government of Canada’s self-assessment tool does not include symptoms related to ageusia/anosmia.
In Canadian provinces and territories, there appears to be significant variation in the inclusion of ageusia/anosmia as a symptom in provincial symptom lists:
- Many jurisdictions (Alberta, Saskatchewan, Manitoba, Ontario, Quebec, New Brunswick, Newfoundland and Labrador, Yukon, and Northwest Territories) have included ageusia/anosmia as a prioritized symptom as part of their-self assessment or symptom-screening questionnaires.
- Other jurisdictions (e.g., British Columbia, Nova Scotia, Prince Edward Island, and Nunavut) have not included these symptoms.

Ontario Scan

The Ontario government’s COVID-19 self-assessment tool includes loss of taste or smell.

The COVID-19 Evidence Synthesis Network is comprised of groups specializing in evidence synthesis and knowledge translation. The group has committed to provide their expertise to provide high-quality, relevant, and timely synthesized research evidence about COVID-19 to inform decision makers as the pandemic continues. The following member of the Network provided an evidence synthesis product that was used to develop this Evidence Synthesis Briefing Note:

Waddell K, Wilson MG, Gauvin FP, Mansilla C, Moat KA, Wang Q, Lavis JN. COVID-19 rapidevidence profile #9: What is the incremental benefit of using a history of sudden loss of taste(ageusia) and/or smell (anosmia) in symptom screening to identify people who may have COVID-19 and need to take appropriate action? Hamilton: McMaster Health Forum, 14 May 2020.