Waste water surveillance to check for Covid prevalence in West Bengal

Kolkata: The state health department will launch a waste water surveillance scheme to look out for Covid-19 presence in the community. Officials of all civic bodies across Bengal have been asked to facilitate the collection of sewerage samples, which will be tested and analysed at National Institute of Biomedical Genomics (NIBMG), Kalyani.

At present, the state is reporting only stray cases of Covid-19, with four to five positive cases on a daily basis. Sources said that the number of daily tests has gone down and only about 1,000 samples are being tested daily in the state.

The positivity also remained below 1% for over four months.

Health officials said looking for the virus in the waste water was a tool for Covid-19 surveillance, and the result will help make public health policies.

“When we look into waste water samples for Covid-19, it will make us understand the disease’s prevalence in the community — whether we are at an endemic stage or there are hidden sub-clinical cases where people don’t go for RT-PCR tests as they remain without symptoms but continue to shed the virus in the waste water. If no virus is found in the waste water, it could mean that the virus has disappeared,” said surgery professor Diptendra Sarkar, member of the Covid-19 task force at Institute of Post Graduate Medical Education and Research.

Officials at Swasthya Bhawan said this surveillance will also be important to identify pockets that are still vulnerable to the virus.

“During all surges, we had come across infected patients with gastroenteritis symptoms. The virus is sometimes shed with stool and urine. Therefore, this kind of surveillance will be useful for public health policies,” said microbiologist Bhaskar Narayan Chaudhuri of Peerless Hospital.

Experts, however, said the virus in waste water samples is not infective any more. Assistant professor Souvik Mukherjee of NIBMG Kalyani has been made the nodal person for the surveillance in Bengal.

“This is part of the pan-India waste water/sewage surveillance. Otherwise, going by lab test reports, the disease’s prevalence is low in Bengal with positivity below one per cent,” said a health official.