INSACOG testing sewage water samples across 55 sites to detect Sars-CoV-2

'This is called environmental surveillance, and India has done this during the polio campaign,' said N K Arora, co-chair, INSACOG

With cases of symptomatic Covid-19 disease on the decline, the Indian Sars-CoV-2 Genomic Consortium (INSACOG) has started surveillance of sewage water samples across 55 sites to detect presence of the Sars-CoV-2 virus. INSACOG also clarified that so far no confirmed case of XE variant has been detected in India.

“This is called environmental surveillance, and India has done this during the polio campaign. Now, the learnings from the polio drive are being used to pick up the Sars-CoV-2 virus from sewage water samples,” said N K Arora, co-chair, INSACOG. He added that very few countries in the world have the technology and capability to detect virus particles from sewage water. India was the first country in the world to do so for polio, Arora said.

The protocol has been set methodically and this is being used to see the virus circulation in the environment. Many people with Covid-19 infection are either asymptomatic, or have very mild influenza-like symptoms. Therefore, many are not opting for testing through RT-PCR anymore.

“We have to be vigilant, and quickly spot any new mutation or variant in circulation in our population. Also, environmental surveillance is a way to confirm the trends we are picking up in routine genomic sampling of individual samples,” Arora told Business Standard.

It also helps to pick up dominant strains in the population, and any geographical trends in the infection scenario.

India’s experience with polio has come in handy. Arora said for every symptomatic case of polio, there are 300-500 asymptomatic cases in the area. Similarly, for every symptomatic Covid-19 case, there are 8-10 asymptomatic Covid cases in the vicinity.

So far, no confirmed case of XE variant has been detected here, Arora said, adding that the INSACOG laboratory network works as a three-layer system. “It’s a wheel-and-cogs-like structure. There are 10 core laboratories that confirm the detection of any variant. Any sample that has undergone genomic sequencing anywhere in the country is sent to INSACOG too routinely,” he explained.

On Wednesday, the Brihanmumbai Municipal Corporation (BMC) declared results of the 11th genome sequencing by the civic body. One sample tested positive for the XE variant of Sars-CoV-2 virus and another has tested positive for Kappa variant, the BMC said.

The Union health ministry, however, said the sample which is being said to be ‘XE’ variant was analysed in detail by genomic experts of INSACOG, who have inferred that the genomic constitution of this variant does not correlate with the genomic picture of ‘XE’ variant.

According to BMC, a 50-year old woman had tested positive for the XE variant. Arora said INSACOG laboratories studied the structure of the virus closely and did not find that it correlates with that of XE.

Also, had it been a case of XE, more such infections would have been picked up in her vicinity by now (the sample was from March 2), Arora felt.

The World Health Organisation (WHO) has flagged off a Covid variant of mutation called XE found in the UK. The global health body has suggested that this could be more transmissible than any Covid strain so far. XE is a combination or recombinant of both sub-variants (BA.1 and BA.2) of Omicron.