COVID-19 | Sewage surveillance shows consistent COVID positivity in 13 out of 28 STPs in Bengaluru

According to the latest report, while STPs in Sarakki, Hulimavu, Lalbagh, Mallasandra Phase 1, Mallathahalli, Lalbagh and Agaram were found to have a higher viral load, Hebbal STP had a relatively lower load

The weekly sewage surveillance for SARS-CoV-2 in 28 STPs of Bengaluru, being jointly conducted by Tata Institute for Genetics and Society (TIGS), NCBS, and Biome Trust in collaboration with BWSSB has shown consistent COVID positivity which has increased slightly, from nine to 13 STPs, for the week ending December 24.

According to the surveillance report, the city-wide wastewater positivity rate for SARS-CoV-2 increased to 46% last week (ending December 24), albeit with a low viral load. This increase in positivity rate is significant compared to 32% reported the previous week (ending December 17) when COVID positivity was found in nine STPs. “This could mean that several thousand persons may actually be shedding the virus in Bengaluru,” TIGS director Rakesh Mishra told The Hindu on Friday.

TIGS, NCBS, and Biome Trust have been conducting weekly sewage surveillance for SARS-CoV-2 in 28 sewersheds of Bengaluru covering much of its 11 million people since August 2021.

“Although the remaining STPs show that the viral RNA load is below the threshold, the possibility of them having viral RNA below the limit of detection cannot be ruled out,” said Dr. Mishra, who is also coordinating a multi-city centre consortium for environmental surveillance, supported by Rockefeller Foundation.

According to the latest report, while STPs in Sarakki, Hulimavu, Lalbagh, Mallasandra Phase 1, Mallathahalli, Lalbagh and Agaram were found to have a higher viral load, Hebbal STP had relatively lower. In the previous week, the highest viral load was detected in Yelahanka Phase 1, Nagasandra Phase 1 and Rajacanal STPs while the lowest was found in Hebbal. These observations indicate that the current viral load is low, close to the detection limit that keeps fluctuating and needs to be closely monitored, said Dr Mishra.

“Last week, the viral load was lowest ever with a mixture of BA.2 sub-lineages. Nonetheless, it shows that there are people infected but not enough to show up in the wastewater. Such environmental surveillance helps to keep track of emerging patterns when used as a complementary tool to clinical testing,” he said.

Elaborating on the report, Farah Ishtiaq, senior scientist, heading the wastewater surveillance programme at TIGS, said the real-time SARS-CoV-2 viral load in STP sites and reported COVID-19 cases show a similar trend in Bengaluru.