In ensuring sufficient precautions and preventive measures be taken in pandemic-driven situations, a very important estimate is of the number of people infected, regions where infection is high and decreasing or increasing trends in viral load. Based on this, civic bodies can decide on targeted vaccination drives, lockdowns and the like. One way to estimate this is by getting people to take COVID test.
However, people do not always comply with testing protocols. In the case of SARS-CoV-2, the high number of asymptomatic and mild infections, also lead to low testing. Finally, if there are one lakh people in a locality, testing one lakh persons every day to monitor the rise and fall of infections is expensive and impractical.
Gauging the parameters
Waste-water based surveillance for COVID-19 comes as an efficient and foolproof way of gauging these parameters. Such a study has been carried out in Hyderabadand Bengaluru by a collaboration between Tata Institute for Genetics and Society (TIGS), Bengaluru, and Centre for Cellular and Molecular Biology (CCMB), Hyderabad.
The study in Hyderabad was carried out for a period of about a year, from July 2020 to August 2021 and obtained data on a population size of about 2.5 lakh. The aim of this study was to develop a protocol and standard operating procedures for doing this, which the researchers hope to hand over to the industry, who can then act as service providers, according to Rakesh Mishra, Director of TIGS, who designed and led the study.
In one year of testing and observations, the researchers were able to spot the temporal dynamics in the viral load in drainage water, which was consistently high from July to November 2020. A slight increase in February 2021 hinted at the second wave which set on in March 2021. This has been published in International Journal of Environmental Research and Public Health.
The group has also studied wastewater samples in Bengaluru, and the learnings from the two cities were very different. While in Bengaluru, they sampled the water from 28 sewage treatment plants (STPs) dotted across the city, the Hyderabad samples were mainly from open drains. The two require very different methods, because in an STP, the water is collected throughout the day, treated and let out again. So it has to be sampled before treatment. Dr. Mishra recalls the commitment and support from the Bruhat Bengaluru Mahanagara Palike (BBMP) and Bangalore Water Supply and Sewerage Board (BWSSB) in the duration of the study.
For the open drainage system, the viral load would be different at different times of the day. After observation, the researchers found that since most of the virus comes from faecal samples, rush hours in the morning — around 8.00 a.m. — are likely to give the best samples. “I can say that we have worked very hard to figure out how to do that, because the viral load is different during different times of the day,” says Dr. Mishra. “If you collect samples too much upstream of the drainage, then only few houses are covered.”
The method has multiple advantages. Trends of increasing or decreasing viral load can be gauged well before the waves take off. “Unlike RT-PCR on a single person’s sample [where the test result can come quickly], it takes us a couple of weeks to do the sequence analysis of the sample… Here you are sequencing thousands of individuals’ virus contribution,” says Dr. Mishra. New variants can be spotted in advance, as can different viruses, such as those that cause dengue, Zika, or TB. This would help the health department to be prepared to deal with epidemics. Studies can monitor antimicrobial resistance genes and point out to civic authorities as to which antibiotics are failing.
“For TIGS, it is a major activity — to do environmental surveillance and ecology of infectious disease — and then understand how patterns are evolving,” says Dr. Mishra.