Since April 2020, RIVM has been examining weekly samples of sewage from sewage treatment plants for the presence of the novel coronavirus. The number of sampling points where RIVM is examining sewage water has recently been expanded from 29 to 80. This means that sewage from approximately 10 million people in the Netherlands is being examined to test for the coronavirus. More particles of the novel coronavirus have been found again in sewage in recent weeks. This corresponds with the increase in the number of infections reported in recent weeks. Steps have been taken to expand research on coronavirus particles in sewage at all of the 300-plus sewage treatment plants in the Netherlands.
As of today, the results of sewage research at the 80 sampling sites, including the regional results, will be posted on the coronavirus dashboard maintained by the Dutch Government. The results will be updated weekly. The coronavirus dashboard shows the average number of virus particles found in sewage at 80 sites.
Coronavirus increase also visible in sewage water
More particles of the novel coronavirus are found in sewage now compared to early July. The rising number of coronavirus particles in sewage corresponds to the increase in the number of infections reported in recent weeks. Like the regional differences in the number of people who tested positive for COVID-19, there are also major differences between regions in terms of the presence of the virus in sewage. Like last week, the highest number of new people who tested positive was reported in the province of South Holland, followed by North Holland and North Brabant. We also see this reflected in the numbers of coronavirus particles in sewage.
Expansion of test sites and new measurement method
As of 20 July, RIVM has expanded its sewage research to 80 sites. The newly added 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. The test sites are also distributed more widely across the Netherlands. The wastewater from the 80 locations comes from about 10 million inhabitants. These samples cover nearly 60% of the Dutch population. 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.
How it works and what it tells us
To prevent polluted water from flowing into nature, the water boards treat the wastewater from households and businesses. This takes place in a sewage treatment plant. Depending on the size of the plant, such a sewage treatment plant may treat the wastewater of several thousand people, or as many as hundreds of thousands of people. The number of virus particles we find in the sewage offers an indication of how the coronavirus is spreading within the Netherlands. It is not possible for RIVM to trace people who are infected with the coronavirus through this research. 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. Sewage research is therefore a valuable addition to the other ongoing surveillance studies by which RIVM is monitoring the spread of the novel coronavirus.
Once a week, researchers test sewage which has been collected over a 24-hour period. The test results show how many virus particles are present in the sewage. 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. These levels are not determined by whether a person infected with the coronavirus has many or few symptoms, or is asymptomatic or presymptomatic.
Based on the current research, it is not yet possible to determine a signal value, as has been done for some of the other data categories on the dashboard. This would require more data, and that is now being collected. The increase in the number of virus particles in sewage is in line with what we see in the other figures. The number of infections is increasing.
RIVM can only carry out this research by partnering with the water boards, the Union of Water Boards and a water company.
To prevent the virus from continuing to spread, it is important for people to comply with the measures: Keep your distance, and stay home and get tested if you have symptoms. Wash your hands, sneeze and cough into your elbow, and use paper tissues.