Using a custom-built olfactory action meter, which determines how well one can smell, a team led by Dr. Nixon Abraham from the Department of Biology at IISER Pune was able to identify people infected with coronavirus but have no typical symptoms. The researchers were able to detect olfactory deficits in 82% of people with asymptomatic infection. The method has 82% sensitivity, 87% specificity and accuracy of 85%.

Now loss of smell, which is one of the symptoms that people infected with novel coronavirus show, can be quickly and accurately measured using a novel method developed by researchers at IISER Pune. Using a custom-built olfactory action meter, which determines how well one can smell, the team led by Dr. Nixon Abraham from the Department of Biology at IISER Pune was able to identify people infected with the virus but have no typical symptoms such as fever, fatigue etc.

To access the olfactory functions of asymptomatic people, the researchers tested 34 patients admitted in isolation wards at B.J. Government Medical College and Sassoon General Hospitals, Pune. The researchers were able to detect olfactory deficits in 82% of people with asymptomatic infection. That only 15% of those with asymptomatic infection were aware of their inability to smell before participating in the test highlights the ability of the new method to detect asymptomatic cases that might otherwise not be detected. The results were published in the journal EClinical Medicine.

The method has 82% sensitivity, 87% specificity and accuracy of 85%.

How the tests were done

The team optimised the experimental parameters by first testing normal healthy participants. The test was performed on 37 healthy participants to assess their ability to detect 10 different odours at varying concentrations — 9.1%, 16.6%, 23.1% and 50% v/v. The odours were presented from lower to higher concentrations and the detection thresholds were based on the ability to detect an odour at two consecutive concentrations. The ability to detect odours was also checked at 50% (v/v) concentration. The lower of these two concentrations was considered as the detection threshold for a participant.

All odours were sequentially delivered at a particular concentration level and then the concentration was increased to the next level. The sequence of odours changed with each concentration level. The odours were delivered for four seconds each with a gap of over 17 seconds between two odours. Both healthy and asymptomatic persons participated in the tests wearing a face mask.

The researchers found that a majority of healthy participants were able to detect eight out of the 10 odorants at 16.6% v/v concentration, which is the second lowest concentration; the two remaining odorants were detected at 23.1% v/v concentration. These experiments identified the parameters for olfactory testing of COVID-19 patients.

People with asymptomatic infection were classified as having either olfactory deficit or deficiency based on their ability to detect odours at different concentration. People are said to have olfactory deficit if they are unable to smell at all four concentrations, and olfactory deficiency if they are unable to detect the odour at two or more out of the four concentrations.

Testing for cognitive impairment 

“We also tested if the cognitive function to detect odour is impaired through olfactory matching accuracy,” Dr. Abraham says. Here, the person if first exposed to one odour and later to another odour and the ability to detect and differentiate and recall the odour are looked at. “Impairment of cognitive function is studied by looking at detection of odours, discrimination between two odours and working memory to recall the odours,” he says. “Only those who can smell odours at more than two concentrations were tested for cognitive function impairment.” The study found significantly reduced matching performances by those with asymptomatic infection compared with healthy people.

They found that 82% of the patient population (27 out of 33) and 13% of healthy participants (5 out of 37) had olfactory deficits. “Olfactory deficits can be seen even in healthy people and this can happen due to different reasons other coronavirus infection,” Dr. Abraham clarifies.

Despite a few healthy participants exhibiting olfactory deficits, Dr. Abraham is confident that the new method can be used for mass screening as the sensitivity is 82%, specificity is 87% and accuracy is 85%.

“Our work has laid the groundwork to use olfactory fitness as one of the prime criteria to identify people with asymptomatic infection. The methods and parameters established by our study can potentially be translated into a sensitive, fast and economical olfaction-based screening assay that can be self-administered by large populations,” he says.

Published in The Hindu on October 16, 2020