Bengaluru to have wastewater surveillance points for possible spike in Covid cases

While the Singasandra ward has found to be twice positive last week, at least 20 sites showed that the viral load increased by 40% or more since last week

A wastewater survey held in several areas has detected traces of the novel coronavirus, indicating the presence of active and undiagnosed cases or non-infectious cases still shedding the microbe.

While the Singasandra ward has found to be twice positive last week, at least 20 sites showed that the viral load increased by 40 per cent or more since last week or 25 per cent or more for the past two weeks.

The Bruhat Bengaluru Mahanagara Palike (BBMP) has vowed to monitor if a similar trend could be found in a two-month period. If they confirm such a trend, they will ramp up testing in those areas and check for an increased number of positive cases.

The data dashboard of Precision Help, an initiative that set up an early warning system through wastewater surveillance to detect disease outbreaks, revealed that 90 samples from 45 sites have been tested twice a week.

“For the week starting November 28, we have 31 per cent of the samples tested being positive compared to 16 per cent in the week starting on November 21 — this is almost a 100 per cent increase in the number of samples testing positive. The last time we had over 35 per cent of samples testing positive was on the week starting on November 21 — this is almost a 100 per cent increase in the number of samples testing positive,” an analysis of the initiative said.

“The last time we had over 35 per cent of samples testing positive was on the week starting June 20. While this is well below the peak numbers of over 60 per cent during May and early June, if we continue to see an upward trend it would be a cause of concern,” according to Precision’s pandemic surveillance dashboard.

A BBMP nodal officer said the 90 samples were spread across 141 wards. “We check for Covid positivity in the sewage and see if there is a spike,” the officer said.

“In November, there is a spike. If a spike is seen in a ward or cluster of wards, what we track is not a single spike, but a series of continuous spikes. If three sites continue to be positive over two months, we correlate this with the actual numbers being reported from the area,” the officer added.

If the actual cases on the ground are fewer and the sewage continues to show a consistent spike, the BBMP ramps up tests in the ward.

“We have six out of 10 Covid positive cases in Mahadevapura and Yelahanka zones. This is consistent with the spike found in the wastewater surveillance,” the official said.

Even if a person is asymptomatic, he/she could be a carrier and sending it out in their excreta.

“That is why we increased tests in Mahadevapura and adjoining areas of the East Zone such as CV Raman Nagar. Accordingly, the cases also spiked,” the official added.

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