RIVMNational Institute for Public Health and the Environment is conducting research on the presence of the coronavirus SARS-CoV-2 in sewage. The coronavirus enters the sewage system via human faeces. By examining the sewage, RIVM wants to map the spread of the coronavirus SARS-CoV-2 at an early stage.

Some people who are infected with the coronavirus SARS-CoV-2 have detectable pieces of the virus in their faeces. They end up in the sewer via the toilet. That often happens before the infected person has symptoms, and therefore also before they have been tested. People who do not have symptoms, but are still infected, could also have the virus in their faeces. By examining the sewage, RIVMNational Institute for Public Health and the Environment can recognise trends and identify at an early stage where the coronavirus SARS-CoV-2 is present. 

Taking samples from sewage all across the Netherlands makes it possible to investigate the spread of the coronavirus. Coronavirus monitoring in sewage research is a way to detect the virus quickly and intervene.

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How does it work

Samples of untreated sewage taken from over 300 sewage treatment plants all over the Netherlands are 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. Genetic material (RNA) from the coronavirus SARS-CoV-2 is isolated from the sewage sample.

Different calculations are then performed, to obtain an overview of the number of virus particles in sewage per 100,000 inhabitants all across the Netherlands. It is also possible to see what the situation looks like in a specific municipality or region. The data is shown on the Corona Dashboard provided by the national government and updated every day.  

Coronavirus monitoring in sewage takes place in close cooperation with the Union of Water Boards and the regional water boards.

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Virus particles in faeces and sewage
Sewage research (National Sewage Surveillance) 
Results of the sewage research

Virus particles in faeces and sewage

Is the virus in the sewage contagious? 
There is no evidence of human infections transmitted via faeces or sewage at this time. Genetic material (RNA) from the coronavirus SARS-CoV-2 has been detected in sewage in the Netherlands. This does not provide any information about whether it is contagious. Several studies did not find any evidence of the presence of infectious virus in wastewater. Some studies have isolated infectious virus from faeces, but other studies did not succeed in doing so.  

Do all people who are infected actually excrete coronavirus particles in their faeces?
No. Not all people who have the coronavirus also have detectable virus particles in their faeces. About 40% do. Some studies suggest higher percentages. Some people who are infected with the coronavirus SARS-CoV-2 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. 

Do all people who have coronavirus particles in their faeces also have symptoms?
No, there could also be coronavirus particles in the faeces of people who do not have any symptoms.

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. Sewage always contains many different pathogens. Faecal matter excreted by sick people, but also by people who are not ill at all, always contains all sorts of pathogens. These pathogens can make other people sick if they are transmitted via hands, water or food. The pathogens are discharged into the sewage via the toilet and sewage system. Personal protective measures for people working with sewage offer effective protection against the various types of pathogens in sewage, including coronaviruses. For that reason, people who work with sewage must wear personal protective equipment appropriate to their work. 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.

What does it mean when virus particles are found in sewage?
RIVMNational Institute for Public Health and the Environment is examining the sewage for genetic material from the coronavirus SARS-CoV-2. The genetic material from the coronavirus SARS-CoV-s is called ribonucleic acid (RNA). Sewage may contain pieces of coronavirus RNA that vary in size. The method detects the presence of these pieces. If virus particles are found in sewage, this means that pieces of the genetic material from the coronavirus are present in the sewage. This means that people are infected with the coronavirus SARS-CoV-2 and their faeces ends up in the sewage. The presence of these particles does not say anything about contagiousness of the sewage.

Sewage research (National Sewage Surveillance)

Why is RIVMNational Institute for Public Health and the Environment researching the coronavirus SARS-CoV-2 in sewage?
RIVM is conducting sewage research to monitor the spread of the coronavirus SARS-CoV-2 among humans. To that end, samples of untreated sewage are collected from all across the Netherlands. Coronavirus monitoring in sewage research is a valuable tool for rapid detection of the virus and intervention. As a result, this research is a good supplement to the national COVID-19 surveillance, such as testing people who have symptoms.

When did RIVM start conducting this research?
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.

Starting in early March, the coronavirus SARS-CoV-2 was 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. At that time, during the first wave, an increase was observed in the levels of coronavirus in sewage, which corresponded to the increase in hospitalisations. Since mid-February, samples of sewage from Schiphol Airport have also been tested; the samples were taken from sewage produced by passengers, employees and, to a lesser extent, from aircraft. From early March on, the coronavirus SARS-CoV-2 was detected in those samples. From April on, RIVM has been taking weekly samples of sewage from sampling points at 29 sewage treatment plants in the Netherlands. In late July, the number of sewage treatment plants was expanded to 80 sites. From 7 September on, all of the more than 300 sewage treatment plants in the Netherlands are sampled one or more times every week. These samples go to RIVM, where they are analysed.

The results are shown on the Corona Dashboard provided by the national government. The results can also be viewed as open data on the RIVM website. Since the beginning of November, the number of virus particles in sewage have been displayed per 100,000 inhabitants. This makes it possible to compare the sewage measurements to other indicators, such as the medical indicators, which are also displayed per 100,000 inhabitants. The figures are also corrected for the amount of sewage that flows through a sewage treatment plant. As a result, the figures can also be compared between municipalities and security regions.

How is RIVM 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. Genetic material (RNA) from the coronavirus SARS-CoV-2 is isolated from the sewage sample. A molecular detection method known as polymerase chain reaction (PCR) is then performed. This method can be used to determine how much RNA from the coronavirus SARS-CoV-2 is present in the sewage.

RIVM then runs a number of calculations and publishes the data in an open data file. 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. More information on the calculating method (in Dutch).

What is the added value of the sewage research?
RIVM is compiling data about the spread of the virus in the Netherlands. We are looking at how many virus particles are present in the sewage per 100,000 inhabitants in a specific area. This corresponds with the viruses from the faecal matter of people who use the toilets in that area. These sewage measurements supplement the results of other studies carried out by RIVM to monitor the coronavirus SARS-CoV-2 – for example, how many people tested positive and in which area. At the same time, we hope that this research will enable us to detect a resurgence of the virus in parts of the Netherlands at an earlier stage. Early detection would enable the Municipal Public Health Service (GGD) and the security region to perform further investigations or to take measures. A protocol for this is being drawn up.

Can sewage research be used to detect infections in a specific area more quickly than other forms of research, such as testing?
It is plausible that an increase in the number of virus particles in sewage can be seen at an earlier stage than an increase in the number of people who tested positive for COVID-19 or hospitalisations. This is probably because the coronavirus SARS-CoV-2 is found in the faeces of some of the coronavirus patients before they develop symptoms.  That has also been demonstrated previously in international research.

It is not yet known how much earlier virus particles are found in sewage than an increase in positive tests or hospitalisations. This may differ from one location to another, and depends on the number of people for which the sewage is processed by a sewage treatment plant where the coronavirus is measured. By conducting more sewage measurements, we can predict more accurately when and what we can expect, and intervene more quickly.

Which locations were 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. For an overview of the measurement locations, see Corona Dashboard.

Does RIVM also include data on wastewater from companies in the research? 
No. The results of the measurements are processed in such a way that only data on sewage from households remains. 

Can sewage research also be used to detect 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.

Sewage analysis can also be used to detect other diseases, medicines, residues, microplastics, hormones, drugs, pesticides, etc. Many chemicals can be found in sewage, offering more insight into the health of the people living in the Netherlands. Options are being explored to see how the sewage study (also known as the National Sewage Surveillance) can be expanded to measure other diseases, viruses and pathogens.

Which organisations in the Netherlands are conducting sewage research?
In the Netherlands, the National Institute for Public Health and the Environment (RIVM) and the KWR Water Research Institute are conducting research at sewage treatment plants.  To that end, RIVM receives samples from all of the over 300 sewage treatment plants (17 million people), on behalf of the Ministry of Health, Welfare and Sports (VWS) and in cooperation with all 21 regional water boards and the Union of Water Boards.  This research is a supplement to other research methods to monitor the spread of the coronavirus SARS-CoV-2 in the Netherlands. The RIVM research data is used to provide public information via the Coronavirus Dashboard of the Dutch Government. Since the research methods used by RIVM and KWR differ, the research results produced by RIVM and KWR cannot be combined.

Results of the sewage research

The results of the sewage research can be found on the Dutch Government’s updated coronavirus dashboard. Since early November, the results are updated on a daily basis. 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 based on the numbers of virus particles in the sewage and the amount of sewage flowing through a sewage treatment plant over time. By applying this model, it is 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 focuses on sewage from a large group of people and cannot be traced back to one individual. However, the information can be traced back to the ‘supply area’ of a sewage treatment plant. This is the area where the coronavirus SARS-CoV-2 enters sewage from the faecal matter of people who use the toilets in that area.  

What can be understood from the figures?
Trends in the number of virus particles in sewage are important, looking at all of the Netherlands, or a specific area. Both an increase and a decrease in the numbers of virus particles in sewage have been observed. At the start of the pandemic, we saw the number of infections in the Netherlands increase and decrease. That was also the case for the number of virus particles in sewage. At the moment, the number of virus particles in sewage is increasing again. That corresponds with what we see in the figures on the number of infections. The number of infections is increasing. More virus particles in sewage means that more virus particles have entered the sewage from faeces of infected people.

Since early November, it has also been possible to compare the measurements from one municipality or security region, because the method corrects for the amount of water flowing through a sewage treatment plant.

Are the results affected by heavy rainfall? 
The amount of rainfall does not affect the measurement. However, when rainfall increases, the number of virus particles per millilitre decreases. To prevent this from influencing the results of the analysis, a specialised sampling method is used. 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 sample, a sample is then taken for the analysis.

The display on the Corona Dashboard has changed since 3 November. Why?
From 3 November on, the Corona Dashboard provided by the national government shows the data from the sewage research per 100,000 inhabitants. This was done because the other data, such as the number of people who tested positive for COVID-19, is also displayed per 100,000 inhabitants. This makes it easier to compare the results from the various types of studies.

Since early November, it has also been possible to compare the measurements from one municipality or security region, because the method corrects for the amount of water flowing through a sewage treatment plant.

Can we still compare figures now that the method has been updated?
The figures from 7 September on have been corrected retroactively. That means that the figures can be compared from 7 September on.

Some locations show very high figures. What could be the explanation for that?
There could be various causes for the high figures at some locations. It could be due to an actual increase in the number of infected people. It could also be due to the design of the sewage system, for example. It may be necessary to conduct additional research.

Can the figures from different municipalities and security regions be compared?
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. As a result, the figures are comparable. 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, from 4 March 2021, the Coronavirus Dashboard also shows sewage monitoring results for smaller municipalities that do not have their 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 still be compared to other municipalities.  

At what level should the situation be considered concerning or serious?
Based on the current research, it is not yet possible to determine a signal value, like an ‘alarm bell’, for sewage research similar to other data categories on the Corona Dashboard. This would require more data, and that is now being collected. Moreover, we also will also need to determine when which actions are needed. This is still in development in close consultation between the Ministry, RIVMNational Institute for Public Health and the Environment and the Municipal Public Health Services (GGDs).