In conversation with Gertjan Medema | MEDICUS 2024 Issue 3

Gertjan Medema dives deep to track wastewater’s unseen secrets

Credit: Courtesy of Gertjan Medema

When COVID-19 swept across the globe, it wasn’t just about tracking the virus’ spread among the symptomatic. To understand the full extent of the pandemic, it was also important to track the virus’ transmission and detect new variants of concern. That meant testing as many people as possible. But how do you do that when not everyone exhibits symptoms or volunteers for testing?

That was when wastewater-based epidemiology emerged as a valuable tool, enabling researchers and public health officials to uncover the virus’ footprints as it spread through populations by analysing wastewater. While the method was adopted in 2003 for detecting the poliovirus by the World Health Organisation (WHO), it was the pandemic that shone a spotlight on its potential.

In this issue, MEDICUS speaks with renowned microbiologist Gertjan Medema, who was awarded the 2024 Lee Kuan Yew Water Prize for his significant contributions to wastewater-based epidemiology. He discusses how wastewater-based epidemiology can inform public health and the potential of this technology beyond COVID-19.

Aerial view of a wastewater treatment plant // Credit: iStock.com /xijian

Get the latest news and features delivered to your inbox.

SUBSCRIBE TO MEDICUS

MEDICUS: Thank you for joining us. Could you explain how wastewater-based epidemiology enhances our understanding of public health?

Gertjan Medema: Wastewater-based epidemiology involves taking a wastewater sample from the community and looking for substances, such as viruses to study what is circulating in the community, for example, in a city. Analysing the data obtained enables us to study the virus concentration and changing trends in the virus concentration. This information helps us deduce what is happening in the community.

For instance, in the Netherlands, we saw a new wave of COVID this summer again—not because there were a lot of people who were sampled, but because we saw it in the wastewater and it corresponded with an increase in hospitalisations. So it gives us a clear indication of what’s circulating in the community.

MEDICUS: What additional insights does this method offer besides detecting viruses in a community?

Gertjan Medema: We can also detect the emergence of new variants by studying the genetic sequence of the virus sequences in wastewater, which was an area of concern for public health officials during COVID.

And we can also do the same for other pathogens, which gives us a lot of information about what is happening on the ground. Take for example, the poliovirus.

We know that some countries still use a weakened live version of the virus for vaccination, and that sometimes ends up in the wastewater, which is what we’d expect. But if we start noticing signs of mutation in the strains that are detected, then we know that we are looking at different versions of the virus, which tells us that the virus may be starting to circulate in the population. This insight is valuable when it comes to deciding the next steps for public health intervention programmes.

MEDICUS: With the advances made during the pandemic, did you anticipate the success of wastewater surveillance for the testing of other viruses?

Gertjan Medema: I think the pandemic has been a pressure cooker that accelerated our progress in this field. What helped, too, was that we already had the methods in place to concentrate waterborne viruses. So when COVID struck, it was a matter of combining this existing methodology with protocols that had been developed to detect SARS-CoV-2 in the clinical samples. The novelty at the onset of the pandemic was that wastewater surveillance worked for this new respiratory virus.

Towards the end of the pandemic, we expanded our arsenal of surveillance targets and found that they also worked well for other types of respiratory viruses such as influenza and the respiratory syncytial virus, and even for non-respiratory viruses such as the mpox virus. And in Singapore and Thailand, we have also seen the recent success of this method in picking up vector-transmitted diseases such as Zika and dengue. So I think it’s amazing how much progress we’ve made as a result of global research efforts in this field.

A member of Prof Medema’s lab, Goffe Elsinga, analyses the collected samples for the presence of viruses. This typically involves concentrating the viral particles, before their genetic material is extracted and quantified in the lab // Credit: Courtesy of Gertjan Medema

MEDICUS: Since its introduction, 72 countries have adopted wastewater surveillance as a means of tracking SARS-CoV-2. What were some of the reasons behind the widespread adoption of this method?

Gertjan Medema: I think one of the main success factors is that it is relatively easy to do. Before the pandemic, we already had an established sampling system in place for extracting viral genetic material from wastewater. So when SARS-CoV-2 hit our shores, we could rapidly adapt these protocols for detecting that virus specifically. That is why so many groups around the world could quickly jump onto this method and collect the information they required.

And because wastewater doesn’t lie, we can also use the intel from this method as a complementary information source that provides us with objective data on what is happening in the community. It is also relatively cost-effective, and since we can get results within a day, this also makes it a great system that can be used as an early warning system.

MEDICUS: How far then are we from using wastewater-based epidemiology in warning us of the next disease X?

Gertjan Medema: It becomes more complex, simply because we are not sure what we are looking for. And it is further complicated by the fact that there are loads of pathogens that can potentially be found in wastewater, from bacteria to plant viruses, from animal viruses to human viruses.

So we must first identify the virus families most likely to trigger the next pandemic. That is when we can study the emerging sequences of these viruses in wastewater and correlate those to what we observe in the clinics to determine if something is happening that warrants our early attention.

Some groups are already working on what such a surveillance system could look like, and what the focus of such a system should be. Beyond deciding which virus families to focus on, other areas for consideration also include the sampling location. And whether we should monitor all the wastewater treatment systems or zoom into potential hotspots for emergence, for example, cities with wet animal markets.

MEDICUS: As the system can pick up animal viruses too, what are some factors that we will need to consider when using wastewater-based epidemiology to study potential spillover events?

Gertjan Medema: As it may not be just humans that contribute to what is in our sewage, we need to be selective about where we obtain the sample from. For example, if we know that the composition of the water in the sewage comprises both rainwater and domestic wastewater, then that might not be an ideal sampling location if the virus is known to be circulating in birds at the time.

In the recent H5N1 episode in dairy cows for example, if there is a dairy farm or factory that is cleaning its tanks and discharging milk into the sewage, that could also create signals that interfere with our analysis. So we are still evaluating the value of such an approach and how we can interpret the data obtained.

MEDICUS: Beyond limitations posed by the sampling site, what are some other considerations when using this technique for public health surveillance?

Gertjan Medema: Ethical concerns have been raised surrounding the use of wastewater surveillance. If a sample is collected from a wastewater treatment plant in a city with a million people, it is unlikely that the results can be traced to an individual. But if you move upstream and monitor a building that houses a patient who is shedding the virus, then it is likely that you’re going to be able to identify who the person is. And if the building is housing migrants, or say, a poorer part of the population, dedicated monitoring of this area may stigmatise the population further, so care should be taken to avoid misusing the technique in ways that stigmatise people. And that’s being discussed now, what the ethical framework for monitoring should be.

There are also ongoing discussions about expanding the accessibility of this approach to ensure equity so that individuals in smaller communities can benefit from this approach. For example, people who live in communities that are smaller and less connected to a wastewater network are less likely to be monitored through such an approach. With nearly half of the world’s population not connected to a sewerage network, there is a push for us to explore alternatives. So we have been experimenting with testing water from drains and streams of informal settlements—and so far, the results have been promising.

Collecting a sample from the river for analysis // Credit: iStock.com / Settapongd Dee-ud

question-mark

Have a question? Send it in and it may be answered in the next issue of MEDICUS!

ASK MEDICUS

MEDICUS: And how does this tie in with your role as scientific coordinator at the WHO Collaborating Centre on Water Quality and Health?

Gertjan Medema: In my role as scientific coordinator, I support the WHO by advising on issues relating to water safety, and in the last couple of years, we have been focused primarily on the public health value of wastewater surveillance. For instance, we look into how wastewater surveillance can be adapted for use in low-resource countries and areas with informal settlements that are not connected to the sewerage network. We also discuss which pathogens to focus on in our surveillance efforts—for example, is it important for them to monitor SARS-CoV-2? Or should they focus on tuberculosis or other types of diseases that are endemic in the region? And currently: how can wastewater help provide an early warning for spreading of mpox clade I?

MEDICUS: And what are your hopes for the future of wastewater-based surveillance?

Gertjan Medema: People tend to forget that wastewater is also a place where pollutants such as pharmaceuticals are being discharged, beyond viruses and pathogens. My dream is to bring about the creation of a comprehensive surveillance system that addresses both public and environmental health challenges through wastewater-based surveillance. And since we already have the tools, I think it is timely that we look at combining these two areas so we can do the best for both worlds.

This interview was conducted and edited by Dr Chua Li Min, Science writer.