‘Post-Diwali Covid case surge in Ahmedabad was reflected in wastewater in Nov 1st week’

A wastewater surveillance on concentration of SARS-CoV-2 RNA genome, conducted across Ahmedabad city between September and November last year, found a higher concentration of the virus in the samples collected in early November, especially in Motera, Ranip and eastern parts of Odhav and Satyam pumping station zones, and warned of a surge in cases that the city eventually saw nearly two weeks later.

During the study, which is a preprint version, 116 samples were used from eight wastewater pumping stations and one sewage treatment plant in Ahmedabad from September 3 to November 26, 2020, and the average effective SARS-Cov-2 RNA genome concentration present in each sample was calculated. It found that the “percentage change in genome concentration level on a particular date was in conjunction with the confirmed cases registered 1-2 weeks later.”

The latest study is an extension of the capability of wastewater surveillance as a predictive tool to determine nearly a fortnight in advance the prevalence of Covid-19 cases. The state health department officials said they, however, use other measures, such as calls to its fever and ambulance helplines, to predict the infection resurgence or decline since the wastewater study results take time and indicated that there is no plan to add wastewater surveillance as a predictive tool in the near future.

The first such study, undertaken between May 8 and 27 last year at the Old Pirana Wastewater Treatment in Ahmedabad, has now been published in the journal ‘Science of Total Environment’. A second study, conducted at four sewage treatment plants in Gandhinagar, between August and September, 2020, had revealed that the local administration can be forewarned by a lead of up to two weeks of an impending spike or decrease in Covid-19 cases by such periodic surveillance. This was published in the journal ‘Environmental Research’.

IIT-Gandhinagar’s Discipline of Earth Science professor Manish Kumar was the lead author in all the three studies.

Co-authored by professor Madhvi Joshi from Gujarat Biotechnology Research Centre (GBRC), Anil Shah from Gujarat Pollution Control Board (GPCB), Vaibhav Srivastava from IIT-Gandhinagar, and Shyamnarayan Dave from UNICEF Gujarat, the study, however, notes that there was “no concrete relationship between virus RNA and daily cases numbers.”

Health Commissioner Jaiprakash Shivhare, who was aware of the studies conducted on wastewater surveillance, said the GBRC is also conducting a similar survey in “other corporation areas”. He added there were other methods in place to predict a rise in cases which take the same time as results of the wastewater study.

“We use a lot of things to plan our strategies and ways to deal with the Covid-19 situation. This (wastewater surveillance) is one input. It gives some indication that in certain areas infection is increasing and cases may increase. But we also use other data, such as calls to 104 fever helpline and 108 ambulance helpline, then cases reported at out-patient departments (OPD) and in-patient departments (IPD) of government and private hospitals. We also use our community medicine department of various medical colleges, and our rapid response teams (to predict possible a spike),” Shivhare said.

The Aarogya Setu data, he added, was also a very good indicator. “These four-five things put together, we start getting the indication that cases are going to rise and this help us know a few days, nearly a week, in advance,” he said.

After samples are collected from the sewage system, they have to undergo a culture test which takes up to four to five days, the health commissioner claimed. “By the time we get the results, it is almost a week. They (researchers) are saying that we can probably predict (through wastewater-based surveillance) a possibly spike or decline in Covid-19 cases two weeks in advance (of which one week is taken up by the time results are out). None of the methods can be very precise, and it is a combination (of several indicators) required to predict a surge or decline in cases,” he added.

Professor Kumar, however, clarified that data from samples taken can be processed and the results can be put on the public domain within 48 hours.

The study also makes a case that the Surveillance of Wastewater for Early Epidemic Prediction (SWEEP)-based model, covering both asymptomatic and pre-symptomatic patients, can help zoning of the city and identifying hotspots as against clinical surveillance, which “hardly classify the city into precise zones where more tests or attention are required.”

Clinical surveillance can also lead to an underestimation of the infection and its spread with pre-symptomatic and asymptomatic cases being missed out, which would otherwise be detected through wastewater surveillance, the study notes. The preprint version states that during the period of sampling, it found the northern areas of Motera and Ranip and eastern parts of Odhav and Satyam zones were highly affected areas in November.

On March 17, the European Commission (EC) in a communication to the European Parliament and the European Council, had recommended tracking the novel coronavirus presence in wastewater across the European Union. “One important use of testing is to track the virus and its variants in wastewater. This can provide rapid and inexpensive information on the presence of a virus and therefore on a possible resurgence… Wastewater surveillance can be used for preventive or early warning purposes, as virus detection in wastewater is a sign of the possible re-emergence of the virus,” the EC communication stated.

The latest study, however, notes that “in a country like India, where sewer systems are not complete and treatment systems are not well managed, it is important to have long-term monitoring for a year at the least, so that precious meaningful data for the developing country can be obtained”.