Ignoring wastewater is a wasted opportunity to improve disease response

During the COVID-19 pandemic, wastewater surveillance emerged as a valuable tool to predict disease burden and help public health administrators shape emergency response. This form of surveillance — estimating viral load in wastewater as a proxy for infection rates — has only been complementary to clinical testing thus far.

In May 2023, WHO declared that COVID-19 is no longer a global health emergency, and most countries will now manage it just like any other infectious disease, with clinical testing becoming rare. Wastewater surveillance assumes even more importance in this scenario, as a permanent smart surveillance strategy and early warning framework that can predict future outbreaks.

The real value of wastewater surveillance is in open sharing of evolving viral trends. The pandemic has influenced the way scientists share crucial data on social media platforms or real time dashboards. For example, in India, the Tata Institute for Genetics and Society (TIGS) shares Bengaluru city wastewater SARS-CoV-2 surveillance data on social media. The researchers also project weekly trends of variant information and supply them to the local municipal government.

Though other Indian cities, including Mumbai, Hyderabad, Pune, Jaipur, Delhi and Ahmedabad, actively conduct wastewater surveillance, only limited data is available publicly. Sharing this information is critical since the virus is now endemic, also to understand the effects of vaccines and prior infections.

Monitoring SARS-CoV-2 ― from zoonotic spillovers to global outbreaks – requires a simple epidemiological tool that can quantify the prevalence and evolution of variant diversity at community level¹. Wastewater-based epidemiology is a rapid and cost-effective alternative to individual testing. It complements clinical data by collecting viral shedding data from both symptomatic as well as asymptomatic people at a community level. SARS-CoV-2 shedding can persist longer in stool samples than in nasopharyngeal swabs² which suggests that stool samples have a longer detection window for the virus than other commonly tested biological samples.

The advantage of wastewater surveillance is that it can project a real-time estimate of the amount of virus circulating in a given population. For instance, in early April 2023, wastewater surveillance in Bengaluru city led by Tata Institute for Genetics and Society, indirectly monitored about 11 million people (more than 80% of the city’s population) and recorded an unofficial outbreak ― the SARS-CoV-2 viral load was much higher than recorded in the severe Omicron wave in January 2022.

However, with very low testing rates now, it is difficult to map this data against the actual infection rate. As the city saw marginal increase in cases, wastewater surveillance was not only crucial in understanding which variants were circulating at the community level, but also in identifying the variants driving the incipient outbreaks. Since wastewater-based monitoring collected variant sequence data at a community level, it provided a comprehensive view of the variant diversity (‘variant soup’) across sewer shed sites. WBE genomic surveillance will be a valuable tool in analysing the contribution of infectious variants.

Wastewater is not wasted water in epidemiology

Monitoring high footfall sites such as airports, flights and hospitals will be important for wastewater surveillance as pandemics and virus variants evolve.

Setting up well-funded wastewater surveillance programmes in a network of cities could capture patterns in emergent diseases and complement clinical testing programmes. The standard method for wastewater-based surveillance of SARS-CoV-2 data is now being used to track trends in other RNA viral targets (influenza A and B, hepatitis A) as well as bacterial and fungal pathogens such as Salmonella sp., Shigella sp., Vibrio cholerae, and antimicrobial resistance genes and drugs. The same wastewater samples could easily be used to test for a number of pathogens at the same time.