COVID-19 transmission: Smell and taste changes can be better indicators of community spread than ER data

A group of researchers at The Pennsylvania State University say that tracking self-reported loss of smell and taste (considered initial symptoms of ) as more effective in assessing community spread than tracking ER visits with suspected infection.

The findings of the study are published in the journal Nature Communications.

Being a respiratory disease, spreads quickly through droplet transmission. Experts had suggested earlier this year that a single positive person can infect about 1.5 to 3 people on average, though the number has been reported to vary in case of crowded situations and superspreaders who may release more respiratory droplets and infect that many more people.

Scientists have been studying the dynamics of spread of the infection to control outbreaks in an area, prevent community spread (a situation where the chain of transmission becomes lost and new patients don’t seem to have any link to previously infected people) and avoid the burdening of healthcare facilities.

An increase or decrease in new cases is being used for making healthcare policies including physical distancing, mandatory masks and lockdowns.

The latest study

For the study, the researchers took data from the Global Consortium for Chemosensory Research Survey, which is an online crowdsourced study released in more than 35 languages.

The recruitment of the study is still going on but the researchers only took data from 7 April to 14 May, 2020. They also took data from the French Government from 7 May, 2020. The latter has been dividing various zones in their country as red and green depending on the extent of the spread of .

The team compared the peak of self-reported loss of smell and taste to the timing of implementation of lockdown measures in France, Italy and the UK, three countries where lockdowns were implemented at different times with different stringency.

Studying all the data, the researchers found that self-reported changes in smell and taste were better correlated with the circulation of the virus and hospitalisation in an area than ER consultations for suspicion of .

The peak of smell and taste changes appeared four days after the lockdown was implemented as compared to ER consultations, which came in after 11 days since the beginning of the lockdown.

Taking data from over 900 individuals in France, the researchers also found that the peak in smell and taste changes were not related to seasonal allergies. Additionally, Google search reports from the same time showed similar patterns, that is, an increase in search for smell and taste changes around the peak of these cases and increase in search for breathing difficulties when CCU admissions increased.

The authors indicated that since changes in smell and taste are early indicators of SARS-CoV-2 infection, this rather than increase in ER consultations could be used to track potential outbreaks of the disease and to decide on the timings of implementation of lockdown and other public health measures.

Not the only way

While the study is new, this is not the only proposed method for studying community spread of .

Previously, some researchers had suggested that SARS-CoV-2, the causative agent of , is shed in the faeces of the patients and hence testing wastewater in various areas can help check for the spread of SARS-CoV-2 in a community.

The Centers for Disease Control and Prevention (CDC), USA, has also started a wastewater testing strategy for the same.

As per the CDC, wastewater testing can help assess both symptomatic and asymptomatic infections since both types of patients shed the virus in their faeces.

For more information, read our article on Local transmission vs community transmission of infection. 

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