A laboratory technician collects river water samples to test for faecal coliform bacteria from the Ganges river in Varanasi on March 5.
| Photo Credit: Getty Images
The story so far: Pathogens (usually bacteria and viruses) that cause diseases in humans and animals, can be tracked in samples taken from the environment, for example, by sampling sewage through wastewater surveillance. This can provide early warnings for potential disease outbreaks.
How does this work?
Samples taken from sewage treatment plants, effluents from hospitals and from public spaces such as railway stations and toilets in airplanes, can be studied to see how the pathogens they contain change from day-to-day. It works because pathogens of interest are shed in the stools or urine of infected individuals. Diseases transmitted by parasitic worms such as roundworms and hookworms can also be monitored through wastewater and soil samples, providing information about the burden of the disease and the effectiveness of control measures.
Rigorous protocols inform the collection of samples. These protocols detail how samples must be collected and processed, and how pathogens are detected and analysed. By following these protocols, comparisons of pathogen load become possible, and whole-genome sequencing enables the identification of variants of the same pathogen.
Why is this important?
Traditionally, the only way to figure out levels of infection in a community was to detect infections in patients, called clinical case detection. However, not all infected people might show symptoms, or might not choose to be tested if symptoms are mild. The number of people who are tested might not reflect the true numbers of those infected.
Environmental surveillance can thus provide important early warning signals of an impending outbreak. It is now known that the levels of pathogen in wastewater can precede, often by more than a week, a rise in infections.
Why do early-warning signals matter?
Understanding how many infected people there are is important for public health planning. The more the amounts of pathogen that circulate, the more likely it is that people will be infected. Preparing for a disease outbreak becomes much easier if there’s more notice.
Wastewater-based epidemiology has been used for over 40 years to track several diseases such as measles, cholera and polio. Such disease surveillance in India, through wastewater, was first initiated in Mumbai for polio in 2001. During the COVID-19 pandemic, similar surveillance programs for COVID-19 were started in five cities, and they continue to this day.
What is India doing?
The Indian Council of Medical Research (ICMR) has recently said that it will initiate wastewater surveillance for 10 viruses across 50 cities. This will enable public health surveillance to pick up any increase in viral load within community settings. This extends ICMR’s involvement in establishing environmental surveillance for viruses, including avian influenza virus, particularly in areas with outbreaks. However, there is scope for improvement. The sharing of data and protocols across institutions and reaching common agreements on templates for surveillance frameworks that are disease-specific is important. Programmatic approaches, rather than project-driven approaches, must be developed that integrate waste-water and other environmental surveillance with routine disease surveillance. Developing a national wastewater surveillance system for India is important.
Moreover, new methodologies are emerging — audio samples of people coughing in public places can be used to examine the prevalence of respiratory conditions, through refined machine learning methods. Thus, the possibilities of environmental surveillance are ever-increasing.
Gautam Menon is Dean, Research and Professor of Physics and Biology, Ashoka University. Views expressed are personal and not of his institution.
Published – October 01, 2025 08:30 am IST