Sewage is always full of many different pathogens, such as bacteria and viruses. Faecal matter excreted by sick people, but also by people who are not ill at all, always contains all sorts of pathogens. Many of these pathogens are discharged into the sewage via faeces. The sewage produced by a group of people, for example a municipality, goes to a sewage treatment plant where the sewage water is purified. There are more than 300 of these treatment plants in the Netherlands.
RIVMNational Institute for Public Health and the Environment constantly collects various types of data in order to control infectious diseases as effectively as possible – including diseases such as COVID-19. One of the ways that RIVM collects data is by conducting research on sewage. The sewage water at sewage treatment plants is tested to detect whether a specific pathogen is present in a population. The results allow researchers to see whether the pathogen is spreading among the population. RIVM is currently testing sewage to check for the novel coronavirus, and has previously done similar testing for the poliovirus and for antibiotic-resistant bacteria.
Starting in early March, the novel coronavirus was found in wastewater 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, 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 novel coronavirus was detected in those samples.
From April on, RIVM has been taking weekly samples of sewage from 29 sewage treatment plants in the Netherlands. The number of sewage treatment plants where RIVM is taking weekly samples of sewage has recently been expanded to 80 sites. These samples come from nearly 60% of the Dutch population: approximately 10 million people. This allows us to identify the municipalities or provinces where levels of the novel coronavirus in sewage are increasing or decreasing. An increase can also be seen in municipalities and provinces where no infected people have been reported yet.
Taking samples from sewage from all across the Netherlands makes it possible to investigate the spread of the coronavirus. Sewage research is a valuable tool for rapid detection and intervention in the event of a possible resurgence of the virus. As a result, this research is a good supplement to the national COVID-19 surveillance, such as testing people who have symptoms. Together with the water boards, RIVM will continue to investigate the sewage system to detect the presence of the novel coronavirus.
Results from trial period in April and May
Since 1 April, RIVM has been testing sewage in the Netherlands to map the spread of the novel coronavirus (SARS-CoV-2). Weekly sewage samples from 29 sewage treatment plants are tested to detect the presence of the virus.
In April and May, the novel coronavirus was found at least once at all sites that were investigated, for example in the sewage of all the provincial capitals of the Netherlands. The peak in COVID-19 patients who were in hospital or had previously been hospitalised occurred around mid-March. In the months that followed, there was a clear decrease in hospital admissions in each province. The sewage samples also showed a decrease in the novel coronavirus in the same months. The novel coronavirus was also found in sewage near 12 sites where people were tested (RIVM and Nivel monitoring stations). See also the news message Sewage research: decline of novel coronavirus in the Netherlands.
Most current news: Coronavirus monitoring in sewage research throughout the Netherlands
Questions and answers about sewage research
Where can I find the results of the analyses?
The results of the sewage research at the 80 sites, including the regional results, can be found on the Dutch Government’s coronavirus dashboard: The results are updated weekly. The data from each sewage treatment plant is available as open data.
Where are the sewage samples for the study being taken?
RIVMNational Institute for Public Health and the Environment is examining sewage from 80 sites across the country. These sites were chosen based on an equal distribution of sewage treatment plants of different sizes. By doing so, towns and cities with many and few inhabitants are represented. For an overview of the sampling locations, see coronavirus dashboard.
Is it possible to determine how many people in the Netherlands have the virus, based on this research?
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. However, this is a rough estimate. This is because not all people who have COVID-19 also have detectable virus particles in their faeces. Some people who are infected with the novel coronavirus have higher levels of virus particles in their faeces than others. There are also infected people who have no virus particles in their faeces at all.
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 novel coronavirus has been detected in sewage in the Netherlands. However, the presence of RNA from the virus does not provide any information about whether it is infectious. 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 carry the coronavirus have detectable virus particles in their faeces. In a large study which analysed data from 21 other studies, an average of 66% of COVID-19 patients had the virus in their faeces. Some people who are infected with the novel coronavirus have higher levels of virus particles in their faeces than others. These levels are not determined by whether a person infected with the coronavirus has many, few or (yet) no symptoms of a coronavirus infection.
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 novel coronavirus enters sewage from the faecal matter of people who use the toilets in that area.
Does RIVM also include data on wastewater from companies in the analysis?
No. The results of the sewage research are processed in such a way that only data from households are included.
Are there any risks to people working in sewage treatment plants?
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:
- Stay at home if you have symptoms and make an appointment to get tested
- Stay 1.5 metres away from other people
- Wash your hands often with soap and water
- Cough and sneeze into your elbow
- Use paper tissues
- Do not shake hands
What does it mean when virus particles are found in sewage?
The method used in this study looks for genetic material of the novel coronavirus in sewage. The genetic material from the novel coronavirus 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 novel coronavirus are present in the sewage. This means that people are infected with the coronavirus, but the presence of these particles does not say anything about whether there are infectious virus particles present in the sewage.
What does ‘XX number of virus particles per millilitre of sewage’ mean?
Trends in the number of virus particles in sewage are important. 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 again increasing. 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. We are now investigating whether this also means that there are more infected people.
Can the results also be correlated to the number of people who tested positive for COVID-19?
No. We do not currently have a way of using the number of virus particles to determine the number of people from whom the faeces and the coronavirus particles originated. We are developing a model based on the number of virus particles in sewage and the amount of sewage flowing through a sewage treatment plant over time, as well as other factors. 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.
Can the analysis be affected by other factors, such as rainwater?
The amount of rainfall does not affect the analysis, but it does however affect the number of virus particles per millilitre. 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 this 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.
What analytical method is used?
An employee of a sewage treatment plant takes a sample of the sewage[CS1] . The sample is transported to RIVM under refrigerated conditions. Genetic material (RNA) from the novel coronavirus is isolated from the sewage sample. A molecular detection method known as PCR is then performed. This method can be used to determine if RNA from the novel coronavirus is present in the sewage. By comparing the results to a predefined quantity of virus particles, it is also possible to determine the number of coronavirus particles. This molecular PCR detection method has previously been described by the Centers for Disease Control in the United States (USCDC).
Why is the analytical method different from the one used before?
Now that more and more sampling points are being added, so more and more sewage samples need to be analysed, RIVM has automated many of the time-consuming manual operations. In order to compare the results of these newly implemented techniques with the methods used previously, extra quality checks are carried out and quality requirements have been drawn up.
Can we still compare figures now that the method has been updated?
Yes. In order to compare the results of these newly implemented techniques with the methods used previously, extra quality checks are carried out and quality requirements have been drawn up.
When will the study include all 300-plus sewage treatment plants?
Starting in September, the coronavirus research in sewage will be expanded from 80 sewage treatment plants to all of the 300-plus plants.
What is the added value of the sewage research?
RIVM can collect location-specific information about the spread of the virus in the Netherlands. This information involves the number of virus particles in the ‘supply area’ of a sewage treatment plant. This corresponds with the viruses from the faecal matter of people who use the toilets in that area. This sewage research supplements the results of other studies carried out by RIVM to monitor the novel coronavirus – 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.
Why is RIVM conducting the sewage research?
Taking samples from sewage from all across the Netherlands makes it possible to investigate the spread of the coronavirus. Sewage research is a valuable tool for rapid detection and intervention in the event of a possible resurgence of the virus. As a result, this research is a good supplement to the national COVID-19 surveillance, such as testing people who have symptoms.
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. Their research differs in the number of sites included in their studies and the research methods used. On behalf of the Ministry of Health, Welfare and Sport (VWS), RIVM is testing sewage as a supplement to other research methods to monitor the spread of the novel coronavirus 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.