COVID-19 and loss of smell: a key symptom in the development of the disease

The Global Consortium for Chemosensory Research (GCCR), an international scientific consortium in which INRAE participates, studied the loss of smell in confirmed COVID-19 cases. In a series of articles, these researchers surveyed patients around the world and found that a partial or total loss of smell was more specific to COVID-19 than other symptoms, and that the detection of this symptom made it possible to track the spread of the disease over time and space. They have created a very simple self-report questionnaire to determine the loss of smell and pinpoint a diagnosis as soon as possible.

With around 45,000 responses, the findings are clear: the most reliable symptom of the onset of COVID-19 is the recent loss of smell without having a stuffy nose.

Many people infected by COVID-19 lose their sense of smell, and to a lesser extent, their sense of taste, which do not necessarily return after they recover. This is why INRAE researchers participating in the GCCR international consortium are working to better understand the changes associated with smell and taste loss caused by this illness. They created an online survey (translated into 30 languages) that lets COVID-19 patients and anyone suffering from a loss of smell or taste describe their symptoms. After compiling around 45,000 responses, the findings are clear: the most reliable symptom of the onset of COVID-19 is the recent loss of smell without having a stuffy nose.

They also analysed Google search frequencies in France and several European countries of keywords such as “loss of smell” and “loss of taste”. The analysis showed that the frequency correlates with the indicators used by health systems: hospital admissions, resuscitations and deaths. Furthermore, the more cases of changes in smell or taste in an area at a given time, the more local hospitals are overwhelmed in the following days. For example, in France, a peak in cases of smell or taste loss observed in late March 2020 was noted around 10 days before a peak in ICU hospital admissions of COVID-19 patients. Detecting this symptom means that the spread of the disease can be tracked precisely over a given time period and geographical area. But how can this information be used to easily diagnose this symptom?

Detecting this symptom means that the spread of the disease can be tracked precisely over a given time period and geographical area.

The GCCR researchers created a very simple self-reported test called ODoR-19. It asked respondents to indicate their ability to smell according to a 10-point scale based on the question: “On a scale of 0 to 10, rate your current ability to smell, indicating 0 if you cannot smell anything and 10 if you have an excellent sense of smell”. After the surveys were analysed, a rating of less than three indicated a moderate to high risk of being diagnosed with COVID-19. The researchers concluded that this simple test could be used by doctors, especially during telemedicine appointments, to speed up and refine their diagnoses.

The GCCR questionnaire on sense of smell and taste loss symptoms:
https://gcchemosensr.org/surveys/en/

References:

• Parma, V. et al. (2020). More Than Smell—COVID-19 Is Associated With Severe Impairment of Smell, Taste, and Chemesthesis. Chemical Senses, 45(7), 609–622. https://doi.org/10.1093/chemse/bjaa041
• Pierron, D. et al. (2020). Smell and taste changes are early indicators of the COVID-19 pandemic and political decision effectiveness. Nature Communications, 11(1), 5152. https://doi.org/10.1038/s41467-020-18963-y
• Gerkin, R. C. et al. (2020). Recent smell loss is the best predictor of COVID-19: a preregistered, cross-sectional study. MedRxiv: The Preprint Server for Health Sciences. https://doi.org/10.1101/2020.07.22.20157263