Researchers from B J Medical College and Indian Institute of Science Education and Research in Pune have reported that by accurately measuring the ability to smell, one could detect an asymptomatic Covid-19 infection. The findings were published on Friday in a paper in EClinicalMedicine, published by The Lancet.
Identifying and isolating asymptomatic patients has been an important strategy to slow the spread of Covid-19.
As new information about the disease began to emerge, the loss of sense of smell (referred to as anosmia) began to be reported among some patients.
Dr Nixon Abraham, whose work at IISER is centered on understanding neural circuits mediating olfactory-driven — the sense of smell — behaviours, problems associated with smelling abilities of Covid-19 patients presented an urgent aspect to explore.
With PhD student Anindya Bhattacharjee and collaborators from 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.
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 odours 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.
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, the team analysed detection indices at varying odour concentrations as well as olfactory matching abilities across various odours. “This allowed us to generate an olfactory function score, which was unique to each individual tested,” says Anindya Bhattacharjee.
The team optimised the experimental parameters by first testing healthy subjects. They then assessed olfaction in asymptomatic patients admitted in the hospital. The method optimised by the team identified olfactory dysfunction in 82 per cent of asymptomatic Covid-19 carriers. In comparison, only 15 per cent of the same set of patients reported a loss of olfaction in self-reporting paradigms.
Using this method, the team says 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.
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