Wastewater surveillance, key tool to spy on diseases, will now cover 50 cities: How will this help prevent outbreaks?

Why is this coverage arc significant?

Such an expansion has significant public health implications since it is being done with the aim of detecting potential outbreaks early, as well as identifying unusual patterns that may indicate a public health concern.

The surveillance will also study patterns of antimicrobial resistance — a global public health threat — that results in the drugs becoming less effective, making it difficult to treat infections. At present, tracking changes in the susceptibility of different pathogens to available antimicrobials is being done through a network of 60 hospitals across the country. “Now, rather than conducting culture studies only on patients coming to these hospitals, these will also be studied in wastewater,” said Dr Bahl.

While antimicrobial resistance surveillance through a hospital network can provide important trends on which drug continues to work for which disease, it cannot track resistance patterns in the community. Wastewater surveillance, on the other hand, can capture these patterns — even in those who might not go to a hospital for treatment.

How will the surveillance be carried out?

The enhanced surveillance will be carried out through the ICMR’s (Indian Council of Medical Research) flagship national network of Viral Research and Diagnostic Laboratories: specialised facilities that focus on the diagnosis, research and surveillance of viral diseases. In the next few months, these laboratories will supplement the findings from patient samples with surveillance of pathogens discharged in wastewater.

What’s the current surveillance status in India?

There is already strong syndromic surveillance for respiratory infections and influenza-like illnesses — instituted after the 2009 swine flu pandemic and strengthened during Covid-19. Around 1,500 samples from patients, who go to hospitals with respiratory symptoms, are tested every week through this national network of laboratories, according to Dr Bahl.

Earlier, the network passively monitored whatever samples were sent by the hospitals but now the labs actively seek out the samples needed to maintain surveillance. This helps keep an eye on which respiratory diseases — viral infections such as Covid-19, H1N1, or RSV — are in circulation. It also helps pre-empt outbreaks, allowing the public health system, hospitals, and clinics to prepare for them.

Similar syndromic surveillance for fevers, diarrhoea and encephalitis has been initiated recently through the laboratory network. Now, the surveillance will be expanded to wastewater in the coming months.

Such surveillance also helps in quickly identifying the pathogen that might be causing an infection by checking the samples for common pathogens that can cause a disease — instead of testing for them one by one. “And, if we cannot detect the pathogen, then genomic sequencing can be done to find what is causing an outbreak,” said Dr Bahl.

Wastewater surveillance proved to be an effective tool in tracking Covid-19. A study from Mumbai shows that the pathogen was detected in wastewater up to three weeks before clinical diagnosis of cases. Another study from Pune showed that silent waves of Covid-19 after the Omicron wave could be detected in wastewater. The XBB variant was detected 130–253 days before it was clinically identified in patients.