Sewage has always been 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 like 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. These samples cover about a quarter of the Dutch population. 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 in all locations 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 (see maps). The novel coronavirus was also found in sewage near 12 locations where people were tested (RIVM and Nivel monitoring stations).
Questions and answers about sewage research
Where can I find the results of the measurements and analyses?
RIVMNational Institute for Public Health and the Environment will publish the results and analyses of the measurements in July 2020. The publication will be posted on the RIVM website.
Which locations were included in the study?
Sewage treatment plants in the 12 provincial capitals were selected for the research done in April and May. These locations were selected in order to facilitate comparison with data collected at the provincial level (see https://www.rivm.nl/sites/default/files/2020-06/COVID-19_WebSite_rapport_dagelijks_20200622_1029.pdf). There are 38 Nivel/RIVM monitoring stations at GP practices, where people are being tested for the coronavirus; 12 of these monitoring stations were selected. In the municipalities where the 12 monitoring stations are located, researchers took measurements at the sewage treatment plants to detect the presence of the virus in sewage. Three of those 12 locations overlap with the provincial capitals. Measurements also continued at Schiphol Airport and in Tilburg and Kaatsheuvel. Also, locations were selected where a high or low incidence was observed at the end of March. In total, 29 locations were included in the study.
Is it possible to determine how many people in the Netherlands have the virus based on this research?
We are looking into this. It is possible that RIVM may be able to make estimates based on the data from the research, assisted by a model. However, we are not that far along yet.
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 contagious. Two studies did not find any evidence of the presence of infectious virus in wastewater. An infectious sample of the virus has been isolated from faeces in some studies, but this has not been successful in other studies. There is no evidence that people have been infected via sewage.
Do all people who have COVID-19 actually excrete the virus in their faeces?
No. In a large study which analysed data from 21 other studies, 66% of COVID-19 patients were found to excrete the virus in their faeces. Very little information is currently available in the Netherlands regarding the number of people with COVID-19 who also have the virus 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.
Does RIVM also include data on wastewater from companies in the analysis?
No. The results of the measurements are processed in such a way that only data from households remain.
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. That includes 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:
- Wash your hands often with soap and water
- Cough and sneeze into your elbow
- Use paper tissues
- Do not shake hands