This means that the sewage of virtually every Dutch household (over 17 million people) is examined. This happens twice a week. Sewage research is a supplement to the other studies that RIVMNational Institute for Public Health and the Environment is conducting to monitor the coronavirus, such as testing people for COVID-19.
The aim is for sewage surveillance to enable early detection in the event of localised outbreaks. It is also possible to detect and recognise new variants. Since RIVM stores the sewage samples, we can check whether a specific variant was already present in the Netherlands earlier on.
The possibilities of sewage surveillance
Coronavirus monitoring in sewage research is made possible by a partnership between RIVM and the 21 regional water boards, as mandated by the Ministry of Health, Welfare and Sport (VWS). These partners are considering future deployment of sewage surveillance for broader applications. Sewage can yield information at the local, regional and national levels about obesity, diabetes, certain forms of cancer, medication and drug usage, microplastics and pesticides. In essence, sewage can be considered an indicator of the health of the country’s population. This form of research also offers possibilities to monitor dangerous substances (such as PFAS, other Substances of Very High Concern, and pesticides) and to support forensic investigations by detecting drug residues. Further research is needed to determine what possibilities are available and what is feasible.
How does it work
Virus particles can enter the sewage system via human faeces from people who are infected. About half of infected people have the virus in their faeces. That includes people with and without symptoms. Sewage flows through the sewer system to the over 300 sewage treatment plants in the Netherlands. Samples of untreated sewage are taken at these plants, refrigerated and sent to RIVMNational Institute for Public Health and the Environment . Researchers at RIVM analyse the samples and figure out how many coronavirus particles they contain. The results are shown on the Coronavirus Dashboard provided by the national government. The results can also be viewed as open data on the RIVM website.
Sewage research from the beginning to now
Sewage research is not new. RIVM is currently testing sewage to check for the novel coronavirus, but also does similar testing for the poliovirus and for antibiotic-resistant bacteria.
- The first reports that the coronavirus SARS-CoV-2 was spreading in Europe were received at the start of 2020. RIVM started testing samples of sewage from Schiphol Airport in mid-February 2020. From early March on, the virus was detected in those samples. Around the same time, the virus was also found in sewage from Tilburg and Kaatsheuvel. The virus was detected shortly after the first COVID-19 patient was reported in the Netherlands on 27 February 2020.
- Sewage surveillance was expanded over the course of 2020. Since 7 September 2020, all of the more than 300 sewage treatment plants in the Netherlands have been included in the sampling.
- From January 2021 on, RIVM also started investigating the presence of different variants of the coronavirus in sewage
Virus particles in faeces and sewage
Do all people who are infected actually excrete coronavirus particles in their faeces (poop)?
No. About 50% of infected people also have detectable virus particles in their faeces (poop). Some people who are infected have higher levels of virus particles in their faeces than others. These levels are not determined by whether a person has many or few symptoms, or is asymptomatic or presymptomatic.
Are there additional risks to people working with sewage?
People who work with sewage should avoid direct contact with the sewage, and should avoid ingesting, swallowing and/or breathing in spray or mist from the water. Personal protective measures for people working with sewage offer effective protection against the various types of pathogens in sewage, including coronaviruses. All these protective measures for safe working practices involving wastewater are listed in the occupational health and safety catalogue of the water management authorities. If you have questions about the Health and Safety Catalogue, please contact your Health and Safety Coordinator. It is also important that employees at the sewage treatment plant follow the hygiene protocols.
Coronavirus monitoring in sewage research (National Sewage Surveillance): how and why?
How is RIVMNational Institute for Public Health and the Environment
conducting the study?
Employees from all of the over 300 sewage treatment plants across the Netherlands take sewage samples. These samples are refrigerated and sent to RIVM. Researchers at RIVM analyse the samples and figure out how many coronavirus particles they contain. This is how they do it: genetic material (RNA) from the virus is isolated from the sewage sample. A molecular detection method known as PCR is then performed. This method enables the researchers to determine how much RNA from the coronavirus SARS-CoV-2 is present in the sewage.
RIVM then calculates the number of virus particles in sewage per 100,000 inhabitants. RIVM publishes the findings in an open database. The Ministry of Health, Welfare and Sport (VWS) processes the data and calculates the weekly averages for the Coronavirus Dashboard nationally and at the security region and municipality levels, according to a predefined method designed jointly by RIVM and the Ministry. The results are shown on the Coronavirus Dashboard provided by the national government. A detailed description of the calculation method is provided here.
Which locations are included in the study?
RIVM is investigating sewage from all across the Netherlands. Sewage samples taken from all of the over 300 sewage treatment plants all over the country are sent to RIVM.
Does RIVM also include data on wastewater from companies in the study?
No. The results of the measurements are processed in such a way that only data on sewage from households remains.
Where can I find the sewage research results?
The sewage research results can be found on the Coronavirus Dashboard provided by the national government. The data from each sewage treatment plant is available as open data.
Can the results also be converted into the number of people who tested positive for COVID-19?
No. We do not currently have any way of converting the number of virus particles into the number of infected people. We are developing a model that we make it possible to estimate the number of people from whom the virus originated. This is a rough estimate, because not all people who have COVID-19 also have detectable virus particles in their faeces.
Is it possible to trace patients on the basis of this research?
No. Sewage research investigates sewage from a large group of people and cannot be traced back to one individual or household. However, the information can be traced back to the ‘supply area’ of a sewage treatment plant. That means that it is possible to see which areas have high levels of virus particles in sewage, but not to identify the precise households where those particles originated. That is not important, because we study trends over time and place to follow the spread of the virus in the population, i.e. looking at a large group of people.
Are the results affected by heavy rainfall?
When rainfall increases, there are fewer virus particles per millilitre of water. A specialised sampling method is used to prevent the amount of precipitation from influencing the results of the analysis. A small sample of sewage is taken periodically over a 24-hour period. The size of the sample depends on the volume of sewage flowing through the sewage treatment plant (known as the flow rate or discharge). If there is a lot of rain, and thus a lot of water flowing through the plant, a larger sample is taken than if there is little or no rainfall. By combining and mixing all these small samples, it is possible to achieve a sample that is representative of the amount of sewage that has passed through the sewage treatment plant in the last 24 hours. From that mixed cumulative sample, a sample is then taken for the analysis. As a result, the amount of rainfall does not affect our measurements. RIVM is conducting further research to determine whether rainfall affects the sewage system.
Can we compare the figures (on the number of virus particles in sewage) from different municipalities and security regions?
Yes, that is possible. In all municipalities and security regions, the sewage measurements are calculated and displayed in the same way: the average number of virus particles in sewage per 100,000 inhabitants. This makes it possible to compare the figures. The data for all locations is also corrected for the volume of sewage flowing into a sewage treatment plant (flow rate) when the measurements are made. This corrects for any influence from rainfall.
Are the sewage measurements for all the municipalities in the Netherlands displayed on the Coronavirus Dashboard? Even the small municipalities that do not have their own sewage treatment plant?
Yes, every municipality has its own sewer measurements. This is the case even if it does not have its own sewage treatment plant. By using the measurements from all the sewage treatment plants that serve a municipality, as well as population distribution statistics provided by Statistics Netherlands (CBS), we can also calculate the number of virus particles in sewage for municipalities without their own sewage treatment plant. Since the measurements are presented per 100,000 inhabitants, the figures can be compared to other municipalities.
Why is sewage research important?
Sewage research is a supplement to the other studies that RIVM is conducting to monitor the coronavirus, such as testing people for COVID-19. Trends in sewage surveillance figures can inform us about the increase or decrease of virus particles in sewage from people who are infected, with or without symptoms. At the same time, we hope that sewage research will enable us to detect a resurgence of the virus at an earlier stage. Early detection would enable the local GGD and municipal authorities to investigate further. To that end, RIVM is working with the GGDs, water boards and municipalities to develop an action plan with clearly defined steps.
Can sewage research be used to make predictions?
In the first and second wave of the pandemic (in 2020), sewage surveillance figures rose in advance of such indicators as positive COVID-19 tests and hospital admissions. Sewage surveillance figures showed that the virus was surging, alerting us earlier than the other indicators. In the current phase of the pandemic (2021), sewage surveillance figures are more in sync with positive tests and hospital admissions.
Sometimes a specific location shows very high levels of virus particles in sewage surveillance. What could be the explanation for that?
High levels of virus particles detected in sewage surveillance could mean that there is an increase in the number of infections. However, that connection is not entirely certain. The number of virus particles excreted by a single infected person could be high or low, and some infected people do not excrete any virus particles at all. That means that it is impossible to know how many people produced the virus particles. When sewage surveillance figures for a specific location are exceptionally high, RIVM always does an extra check to see if the measurement was carried out correctly, if the data is correct and if the calculations were done properly. If so, further research may be carried out in consultation with the municipality, the local GGD and the regional water board. A spike may mean that something is wrong with the sewage system. If we are sure that everything in the sewage system is normal, then there is probably an increase in the number of infections.
At what level should the situation be considered concerning or serious?
Since early June 2021, early indicators for sewage surveillance were added to the Coronavirus Dashboard provided by the national government. The sewage research results on the Coronavirus Dashboard are displayed in colours ranging from light blue to dark blue. The darker the colour, the more serious the situation. Early indicators for positive tests and hospital admissions have been available for some time now.
Can sewage research also be used to identify different variants?
Since January 2021, RIVM has also been investigating sewage to detect new variants of the coronavirus, using a specialised method known as sequencing. Some of the sampled sewage is stored at RIVM. Sewage samples are stored for extended periods of time to allow for additional research at a later date. This makes it possible to check whether a specific variant was already present in the Netherlands earlier on.
Sewage research: the future
How long will sewage research related to COVID-19 continue?
RIVMNational Institute for Public Health and the Environment , the water boards and the Ministry of Health, Welfare and Sport (VWS) have agreed to continue coronavirus monitoring in sewage research until at least the end of 2025. In the next few years, it will definitely be necessary to keep monitoring the spread of the coronavirus SARS-CoV-2. Keeping track of the virus remains important.
Can sewage research be deployed in a broader context? For example to detect and monitor other diseases?
Sewage research is not new. RIVM is currently testing sewage to check for the coronavirus SARS-CoV-2, but also does similar testing for the poliovirus and for antibiotic-resistant bacteria. In the next few months, RIVM will be working closely with the Ministry of Health, Welfare and Sport (VWS) and the water boards to explore the directions in which sewage research can be expanded in the future. For example, it could be used to detect other diseases, medicine residues, microplastics, hormones, drugs and pesticides. Many chemicals can be found in sewage, offering more insight into the health and lifestyle of the people living in the Netherlands.