Pune: Since late April, researchers at the CSIR-National Chemical Laboratory (NCL) have detected a steady presence of the Covid-19 virus across all ten sewage treatment plants (STPs) in Pune. This consistent detection mirrors trends observed ahead of previous pandemic waves, raising concerns among scientists monitoring the city’s wastewater.
Dr Mahesh S. Dharne, a microbiologist at NCL, explained that while the current increase in viral traces is gradual, the trajectory strongly resembles earlier surges. “We first detected SARS-CoV-2 in sewage samples on April 22. From May 6 onwards, every STP has shown persistent positivity through RT-PCR testing,” he noted.
Wastewater-based epidemiology has become a crucial early warning tool in tracking the spread of infectious diseases like Covid-19. By analyzing genetic fragments of the virus found in sewage, scientists can monitor both symptomatic and asymptomatic infections at the community level—offering insights that are often ahead of clinical testing trends.
NCL remains the sole agency in Pune systematically monitoring sewage data from all major STPs. This surveillance effort has previously provided early alerts for outbreaks involving Omicron and its sub-variants. Dr Dharne shared that the lab’s renewed focus came in response to a rise in cases internationally, particularly in Singapore. “We had archived several samples. The global uptick prompted us to re-examine our local data,” he explained.
Currently, approximately 40 of the 60 weekly samples collected from Pune’s treatment plants are returning positive results. Despite the monsoon’s interference—rainwater likely diluted sewage, possibly underestimating the actual spread—the virus’s presence has remained consistent since April. “As the weather stabilizes, we expect this week’s data—due Friday or Saturday—to provide a clearer picture,” said Dr Dharne.
While RT-PCR testing of wastewater can reveal viral concentration levels, it does not identify specific variants. “We can’t pinpoint which variant is circulating, but the rising viral load is similar to what we’ve seen before previous waves,” he cautioned.
To support public health response efforts, NCL shares its findings with key health bodies, including the Maharashtra Covid-19 Task Force, the Integrated Disease Surveillance Programme (IDSP), and the National Centre for Disease Control (NCDC) in New Delhi.
This initiative forms part of the Four City Surveillance Programme, launched in August 2021 with support from the Rockefeller Foundation (USA). Alongside Pune, the program covers Hyderabad, Bengaluru, and Sonepat. It is a collaborative effort involving CSIR-CCMB, TIGS-NCBS, Ashoka University, and the Pune Knowledge Cluster, under the guidance of experts such as Dr Rakesh Mishra (TIGS), Dr L.S. Shashidhara (NCBS), and Dr Vinay Nandikoori (CCMB).
