How a Kerala-based scientist is using sewage to detect Covid-19 in Australia

Sewage is something most people are repulsed by. The idea of stepping into sewage is something most people would not consider if given a choice; yet a scientist has turned this amalgamation of refuse into a novel way to detect and map the spread of Covid-19.

Sudhi Payyappat, a Kerala-born scientist employed at Sydney Water as a technical specialist, is leading a team to examine dozens of sewage samples from wastewater treatment plants across New South Wales in Australia.

Payyappat's idea for mapping Covid-19 is simple: A person will begin 'shedding' fragments of the coronavirus within three days of infection via excrements. These fragments travel through sewage pipes, end up in treatment plants and be detected through testing in labs, enabling local health departments to detect infection in a community.

“I was really surprised by the sensitivity of this method. If one person is shedding the virus in a catchment of a 20,000-30,000 population, we will be able to pick it up in the treatment plant. It has a huge economic potential as it is the same as monitoring that many people. It has helped in containing the spread of the infection,” Payyappat told The Indian Express.

“Once you get the virus, you may show symptoms only from 6 or 7 days onwards, or you may be an asymptomatic carrier. But you start shedding the virus within three days. That gives us plenty of time to arrest the spread of infection. Through this, we can also detect how the degree of infection in a community is changing," he told the publication.

Payyappat, who hails from Thrissur in Kerala, was incidentally visiting the state when the first case of Covid-19 in India was reported in Thrissur on January 30 last year. After he returned to Australia, he learnt that people were shedding the virus through their stools, which ended up in the sewage system.

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"We have an organisation here called Water Research Australia (WRA). It created a research programme called Collaboration on Sewage Surveillance for SARS-CoV-2. I am part of the research programme. When I got the early successful detection, I passed on the information to other partners. They adopted my method which is being run across the country now," Payyappat told The Indian Express.

The process of extracting the genetic markers of Covid-19 from a sewage sample is highly complex. The samples collected by personnel on the field are transported to the lab in refrigerated conditions with temperature not exceeding ten degrees. They then go through a complex three-stage analysis, starting with concentration, followed by extraction of the virus nucleic acid and finally detection through qPCR, the report explained.

"Since we don’t have as many cases in Australia as other countries, the process of extracting the virus' genetic markers was a challenging one, as there is a massive dilution happening, and sewage is a difficult matrix with industrial waste and chemical compounds which can interfere with the detection of the virus," Payyappat said.