Places without centralised sewage treatment systems can still effectively use wastewater to catch outbreaks of dangerous diseases before travel across borders, according to a collaborative international study.

Everyday, humans release clues about our health into the wastewater system via toilets, sinks, showers and bathtubs. In wealthier countries like the US, sewer networks collect tiny bits of faeces, urine, skin cells, sweat, and even blood. In the right hands, this creates a snapshot of what is happening in our bodies.

The Covid-19 pandemic spurred the rapid rise of wastewater testing, which helped health officials around the world spot outbreaks early. Wastewater testing offers a real-time, non-invasive way to estimate how many people may be affected by a health condition in a community, particularly when traditional health systems cannot.

To date, this powerful tool had only been proven to work where modern sewerage systems exist—even though the next pandemic could begin anywhere. To help fill this gap, researchers from the Gerald J and Dorothy R Friedman School of Nutrition Science & Policy and Cummings School of Veterinary Medicine at Tufts University in Massachusetts, US, came together with Tufts University School of Medicine and a team of international collaborators to see whether wastewater testing could work in places without comprehensive sewage management systems.

The team showed that they could detect signs of disease in wastewater flowing through open channels in two urban neighbourhoods and a poultry market in West Africa.

In this Q&A, Daniele Lantagne, a research professor at Tufts University and the study’s senior author, explains why making wastewater surveillance more accessible is so important.

What is wastewater surveillance and how does it work?

Most Americans first heard about wastewater surveillance during the Covid-19 pandemic, when it helped public health officials track outbreaks, but the idea has been around much longer. For example, the Global Polio Eradication Initiative has used it to confirm that countries are free of polio, and even law enforcement has tapped it to trace illegal drug production.

Today, across the United States, sewage from many cities and towns will flow into a single wastewater treatment plant. Giant pipes carry this wastewater in, and special devices can take small samples from these pipes every few minutes. Health officials may have only tested for the virus that causes Covid-19 at first, but now many regions also test for viruses that cause flu and RSV [respiratory syncytial virus] and other pathogens.

What problem were you trying to solve in your new study?

In wealthier countries like the United States, wastewater testing works because we have pipes and treatment plants that collect sewage in one place. That makes it easy to sample and test the water, but around the world, more than 3.5 billion people do not have access to this kind of safely managed sanitation. Waste often ends up in open drains or pits, so the usual wastewater testing methods just do not work.

Our team wanted to find out if we could make this tool useful in places without modern plumbing and sewer systems. That meant figuring out where to collect samples, what diseases to test for, and how to train local teams to do the work themselves.

What did your team find?

We focused on two kinds of high-risk places in Côte d’Ivoire in West Africa: open wastewater channels from crowded urban neighbourhoods and water used to clean poultry in local markets. We wanted to see if we could detect two major threats: SARS-CoV-2, the virus behind Covid-19, and influenza A, a virus that causes bird flu.

Over 12 weeks, we collected samples and had them tested in local labs. Nearly half of the human wastewater samples showed signs of Covid-19, and we found flu virus in some of the poultry wastewater.

What is exciting is that this is one of the first times wastewater surveillance has been used in such low-resource settings. We also trained local scientists and proved that this kind of testing can work —even without expensive infrastructure.

Why does this matter for people around the world?

Infectious diseases do not respect borders. If a dangerous virus like Ebola emerges in Côte d’Ivoire, it is just one plane ride away from the US. As people move into previously remote areas, we are seeing more chances for new diseases to jump from animals to humans.

Catching those threats early—right where they begin—is the best way to prevent them from spreading. That is why the US has long invested in public health systems around the world. Wastewater surveillance is another smart tool in that toolbox.

How else should we tap the power of wastewater testing?

We need to keep asking when wastewater testing will make the most impact. It is especially useful in places where diseases spread silently— when people do not show symptoms or cannot access testing.

For example, Lassa fever, a disease carried by rats in West Africa, is likely far more widespread than we realise. It often looks like malaria, so it is frequently misdiagnosed.While many people have mild symptoms, others get very sick with severe hemorrhagic illness —similar to Ebola—and die. Wastewater could help track its true spread.

During our study, we were about to test wastewater from a rural hospital in Côte d’Ivoire where all the waste flows untreated into a nearby forest. We expected to detect the Lassa virus—which the hospital cannot test for — but the project was cancelled due to federal budget cuts affecting our funder, the US Agency for International Development (USAID). That kind of setback shows why we need more support to prove that viruses like Lassa can be detected in wastewater using low-cost, locally available tools.

The study was published in PLOS Water.