Some of the most notable symptoms of coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), are hyposmia and anosmia. Hyposmia is the partial loss of smell, and anosmia is the complete loss of smell.
Along with the loss of smell is the loss of taste, also known as ageusia, fever, cough, headache, and difficulty of breathing. With the skyrocketing number of cases globally, it is important to find easy, cost-effective, and fast screening tests.
Researchers at the Weizmann Institute of Science and other institutions developed a new tool to help detect COVID-19 infection. The team developed and tested a real-time tool to measure olfactory perception impairment by asking the participants to smell household odorants.
In the study, which was published on the pre-print medRxiv* server, the team found that olfactory ratings were indicative of COVID-19 status in a country. Further, they found remarkable indicative power at the individual level, with a 90 percent sensitivity and 80 percent specificity.
The coronavirus pandemic first emerged in Wuhan City, China in December 2019. Since then, the virus has spread to 192 countries and territories, infecting more than 112.22 million cases globally.
During the first few months of the pandemic, the common signs and symptoms reported included fever, cough, and breathing difficulty. When the virus spread to more people, other symptoms were reported, including loss of taste, loss of smell, diarrhea, headache, and body pains, among others.
It is still unclear how COVID-19 could cause loss of smell. Some evidence showed that SARS-CoV-2 binds to a protein called the angiotensin-converting enzyme 2 (ACE2), which is abundantly found in the nose and mouth.
The presence of ACE2 on cells that surround nerve cells may mean that when the virus invades the host cells, it could also affect these nearby nerve cells, causing loss of smell and taste.
In the study, the researchers developed an online tool wherein each participant selected 5 of 71 household odorants. They smelled and rated each using a visual analog scale for perceived intensity and pleasantness. These are considered primary dimensions of olfactory perception.
The participants answered a common symptom-check questionnaire for COVID-19, reporting cough, fever, loss of smell, and loss of taste.
The researchers collected data from more than 12,000 participants across 134 countries from March 25, 2020, to September 3, 2020. Among these, 348 participants reported positive COVID-19 test results, 400 individuals had a negative result, and the status of the 11,272 participants was unknown.
Based on the findings, the researchers observed that olfactory ratings were tied to COVID-19 status in a country, which is correlated with national infection rates. They concluded that olfactory testing was highly effective in asymptomatic participants.
Olfactory testing is more effective than symptom checking A. ROCs for all participants who smelled Olive Oil (n = 5,167 participants), based on odor intensity (blue) or reported symptoms (red). B. ROCs for all participants who smelled Olive Oil and had symptoms (n = 2,627 participants), based on odor intensity (blue) or reported symptoms (red). C. ROCs for all participants who had no symptoms (n = 7,740 participants), based on odor intensity (blue) or reported symptoms (red). D. ROCs based on the olfactory perceptual fingerprint (blue) or symptom reports (red) (test-set n = 60 participants). E. ROCs based on the olfactory perceptual fingerprint (blue) or symptom reports (red), when all participants are symptomatic (test-set n = 60 participants). Error bars on the ROCs: 95% pointwise confidence interval. Error bars for the AUC: Confidence interval derived standard deviation.
Moreover, the study findings support that olfactory testing could be an excellent tool for border control to distinguish people carry the infection. For instance, a symptoms checker will tag a person with fever, cough, and colds as COVID-19 suspected cases but may miss asymptomatic carriers.
In this, the current odorant-based olfactory test stands apart from symptom-checkers (including olfactory symptom-checkers), and even from antigen tests to potentially provide the first line of screening that can help halt disease progression at the population level,” the researchers explained in the study.
With the long-term persistence of olfactory impairments in people with COVID-19, the tool developed by the researchers can be effective at providing the first line of screening. The tool can be a cost-effective tool to detect initial infection, which could lead to the rapid screening of potential carriers.
Screening and testing effectively can help mitigate the pandemic. When infected people are isolated promptly, transmission can be reduced.
Finding a fast and easy screening tool can help control the spread of the pandemic, which has killed more than 2.48 million people worldwide.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.