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On the sense of smell in asymptomatic COVID-19 infection  Oct 17, 2020

Nose to the rescue: Using the sense of smell to identify asymptomatic COVID-19 infection

In a paper published in The Lancet’s EClinicalMedicine, in collaboration with the BJ Medical College and Sassoon General Hospitals in Pune, researchers from IISER Pune report that by accurately measuring the ability to smell, one could detect an asymptomatic COVID-19 infection caused by SARS-CoV-2 virus.

The COVID-19 pandemic has posed a daunting challenge to the global community as a large number of individuals that are infected with COVID-19 do not show any symptoms of the infection but can transmit the infection. Identifying and isolating asymptomatic patients has therefore been an important strategy to slow the spread of the COVID-19 pandemic.

As new information about the disease and the virus began to emerge, a curious symptom, that of the loss of sense of smell (referred to as anosmia), began to be reported among some of the COVID-19 patients.

Faculty member Dr. Nixon Abraham (Left) and PhD student Anindya Bhattacharjee (Photo Credit: Dr. Abraham's Lab webpage)

For faculty member Dr. Nixon Abraham whose work is centered on understanding neural circuits mediating olfactory-driven (related to smell) behaviors, problems associated with the smelling abilities of COVID-19 patients presented an urgent and important aspect to explore.

With PhD student Anindya Bhattacharjee and collaborators from the BJ Medical College and Sassoon General Hospitals in Pune, the team set out to test if anosmia (total loss of sense of smell) / hyposmia (reduction in the ability to smell) could be an indicator of COVID-19 infection in individuals who tested positive for the virus but showed no other typical symptoms of the disease.

Drawing from the core expertise of Dr. Abraham’s research group in testing for olfactory behavior, the team first designed and custom-built an olfactory-action meter, that can determine with precision how well one can smell.


“Our instrument offers many advantages over the existing clinical methods for assessing olfaction. It delivers odors in a controlled fashion, assesses the olfactory health status in less than 20 minutes of testing, and can innocuously quantify deficits under infective conditions as it has built-in safety precautions to prevent cross-contamination,” says Dr. Abraham.

For this study, the team used odorous substances of varying physico-chemical properties that allowed them to collect more than 3600 readouts from 71 subjects, including normal healthy subjects and asymptomatic COVID-19 patients.

Through this method of screening, the team analysed detection indices at varying odor concentrations as well as olfactory matching abilities across various odors. “This allowed us to generate an olfactory function score, which was unique to each individual tested”, says Anindya Bhattacharjee, who, along with Dr. Abraham, made these measurements at the BJ Medical College during the COVID-19 lockdown in May this year.

The team optimised the experimental parameters by first testing normal healthy subjects. They then assessed olfaction in asymptomatic COVID-19 patients admitted in the hospital. The method optimised by the team identified olfactory dysfunction in 82% of asymptomatic COVID-19 carriers. In comparison, only 15% of the same set of patients reported a loss of olfaction in self-reporting paradigms.

Using this method, the team says that they can analyse both sensory (pertaining to sensory neurons in the nose) and cognitive aspects (problems at the central nervous system, beyond the nose) of olfaction. “As neuroinvasive properties of SARS-CoV-2 are not known very well, obtaining readouts reflecting the cognitive abilities would be very useful and we are collecting this data right now,” he added.

Speaking on the potential applications of the study, Dr. Abraham said that the study has laid the necessary groundwork to consider olfactory fitness as one of the prime criteria to identify COVID-19 asymptomatic carriers. “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,” said Dr. Abraham.

This research received funding from the DBT/Wellcome Trust India Alliance.

Article Citation:

Quantitative assessment of olfactory dysfunction accurately detects asymptomatic COVID-19 carriers. Anindya S. Bhattacharjee, Samir V. Joshi, Shilpa Naik, Shashikala Sangle and Nixon M. Abraham. EClinicalMedicine (in Press) DOI: 10.1016/j.eclinm.2020.100575

A video summary of the paper is made available by the journal here.

- With inputs from Dr. Nixon Abraham