Wastewater monitoring: 'the James Webb Telescope for population health'

When the COVID-19 pandemic triggered a lockdown across Bangladesh and her research on environmental exposure to heavy metals became impossible to continue, Dr. Rehnuma Haque began a search for some way she could contribute to the pandemic response.

“I knew I had to do something during COVID,” said Dr. Haque, a research scientist at the International Centre for Diarrheal Disease Research, Bangladesh (icddr,b). “I couldn’t just sit at home.”

Then she stumbled upon articles on early wastewater monitoring efforts for COVID in Australia, the Netherlands, Italy, and the United States. “When I read those papers, I was so excited,” said Dr. Haque. “I emailed my supervisor, Dr. Mahbubur Rahman, and said, 'Can we do this?'”

Two months later, in June 2020, Dr. Haque and her colleagues had launched one of the most robust and earliest national wastewater surveillance programs for COVID in a low- or middle-income country (LMIC).

The initiative, which has now been expanded to monitor for cholera, salmonella, and rotavirus and may soon be expanded further to monitor for norovirus and antibiotic resistance, demonstrates the power and potential of wastewater surveillance to serve as a low-cost tool for obtaining real-time meaningful health data at scale to identify emerging risks and guide public health responses.

“It is improving public health outcomes,” said Dr. Haque. “We can see everything going on in the community through wastewater surveillance. You can find everything you are looking for and then prepare a response.”

A single wastewater sample can yield representative data about an entire ward, town, or county and allow LMICs to monitor for emerging pathogens. Compared with clinical monitoring, wastewater monitoring is easier and cheaper to collect, can capture infections that are asymptomatic or before symptoms arise, raises fewer ethical concerns, can be more inclusive and not as prone to sampling biases, can generate a broader range of data, and is unrivaled at quickly generating population-level data.

Wastewater monitoring was first used in the U.S. in 1938 to screen for polio. COVID proved a turning point for the field, expanding interest and increasing investment, said Dr. Alexander G. Shaw, a researcher at Imperial College London who is part of the team that more recently found evidence of polio in London sewage, sparking a massive vaccination campaign.

“Detection of SARS-CoV-2 during the pandemic gave a massive boost to the field of wastewater-based epidemiology,” said Dr. Shaw. “COVID helped build the infrastructure and expand interest in wastewater surveillance. Now we need to make sure that the established infrastructure is fully leveraged, with its deployment and use tailored to generate data that is valuable for public health action.”

The established wastewater surveillance infrastructure is currently mostly concentrated in high-income countries, said Dr. Dhammika Leshan Wannigama, a wastewater surveillance researcher who is on the faculty of medicine at Chulalongkorn University and King Chulalongkorn Memorial Hospital, Thailand. “Unfortunately, when wastewater surveillance was getting a lot of attention early during the COVID pandemic, the first published materials on it were focused on a few high-income countries. And the costs were quite high, discouraging health leaders in LMICs. They thought it was too expensive and too complicated in LMICs.”

But wastewater surveillance is possible and powerful even in Bangladesh, where the sanitation system is very weak, said Dr. Haque. For example, only 20% of Bangladesh’s capital city has access to improved sanitation. While this makes wastewater monitoring more challenging, it is still effective.

“Wastewater surveillance can be as simple as a ‘grab sample’ taken from a ditch on the side of the road,” said Dr. Andrew Singer, principal scientist at the U.K. Center for Ecology and Hydrology, who contributed to the implementation of the U.K.’s wastewater monitoring efforts during the pandemic and serves as an advisor for other wastewater monitoring efforts. “While the quality of the sample will vary, what is important is to be strategic about where you are sampling, when you are sampling, and what you are looking for.”

Dr. Haque and her colleagues started initial sampling focused on monitoring COVID in wastewater from hospitals. Once the team knew its lab and techniques were functioning well, they expanded their monitoring. That required a crash course on topology and connectivity of sewer networks in urban areas and catchment areas in rural communities. In the process, she and her colleagues obtained and tested about 800 samples across the country, from Dhaka to the Rohinga refugee camp in Cox’s Bazar.

“Initially, we were just playing around, trying to figure out the best places and times to sample, to minimize debris and obtain samples that weren’t useless because of high levels of inhibitors, such as washing powder and bleach,” said Dr. Haque.

But over time, the team developed a robust network of representative sampling sites and processes that has helped the country identify, respond to, and prevent a wide variety of threats.

Dr. Haque and her colleagues identified a new variant of COVID four months before the variant was clinically detected and more recently, they found that rotavirus and salmonella incidents peak 10 to 14 days before they are reported at health facilities – identifying hot spots and giving public health leaders an opportunity to prepare a response.

Each week, a group of stakeholders — politicians, ministry of health officials, public health experts, academics, sanitation experts, and virologists, among others — meets to review the most recent data and discuss possible responses. Those responses might include public health communication campaigns, immunization campaigns, and alerting clinicians at local public health centers to prepare for an influx of patients.

Dr. Wannigama’s work in Thailand, which started as a wastewater monitoring program looking for antibiotic resistance in a hospital and quickly shifted to COVID at the start of the pandemic, now monitors wastewater for RSV (respiratory syncytial virus), influenza, norovirus, rotavirus, and monkeypox. He and his team have also been able to predict outbreaks of disease two weeks before they are clinically detected in urban areas and three weeks before they are clinically detected in rural areas.

Wastewater monitoring, when strategically designed to do so, can also improve equity in health systems by reaching communities and individuals that otherwise cannot or do not access the health system for clinical diagnosis.

That’s because, even after we flush, our waste is highly segregated, explained Dr. Singer. Examine a sample from a city’s sewer system and you’ll have captured all the demographics within that city. However, analyze sewage downstream of a hospital, a nightclub, a care home, or a university residence hall, and you’ll monitor particular socio-economic groups and specific age bands within those groups. Examine a sample from a train station and you’ll reach an entirely different socioeconomic group.

Bangladesh’s program is designed with equity in mind. “We are not only analyzing the waste of rich people who can afford to visit hospitals,” said Dr. Haque. “The waste we are monitoring must represent all people. If done strategically, wastewater monitoring can be most equitable and allow us to monitor even the most remote and vulnerable rural communities.”

Dr. Wannigama’s work in Thailand also aims for equity by including collection points in fresh markets, where low-income people buy and sell food; in pit latrines in hilltop villages; and even in remote areas near Thailand’s porous borders with its neighbors.

The decline in costs for the associated lab equipment over the past two years presents an opportunity for LMICs, said Dr. Wannigama. Today, establishing a lab capable of monitoring wastewater can cost less than US$50,000, requires just two or three technicians to run, and can process a sample for less than US$10.

That has prompted growing interest and opportunities in LMICs. Ghana's wastewater monitoring program focused on detecting typhoid is currently expanding to detect cholera and hepatitis. Malawi is monitoring wastewater at hospitals in its capital for antibiotic resistance and has monitored wastewater for typhoid. Nigeria is also establishing a wastewater monitoring program. India, which used wastewater sampling to help it eradicate polio – detecting a single person infected out of a population sample of 10,000 – has a variety of wastewater monitoring efforts under way, including researchers monitoring wastewater in Kolkata for typhoid. This effort identified a previously unknown high burden of typhoid among hildren and prompted health leaders to consider early childhood typhoid vaccination. A recent article in the Lancet Global Health provided a survey of wastewater monitoring efforts across 43 countries. A global dashboard established during COVID identifies 72 countries currently monitoring wastewater for the virus, many of which have since expanded beyond COVID.

“When I look up at the heavens from my home in England, I can see only a few dozen stars,” said Dr. Singer. “Give me a telescope and I will find many more. As these wastewater monitoring efforts expand, we will find viruses we didn’t know existed. Wastewater surveillance is the James Webb Telescope for population health. We can now monitor population health and identify and counter the tens or possibly hundreds of organisms that silently — or not — prey upon us all the time, in near-real time. We have entered a new paradigm in public health.”