Several international studies have shown that people who are infected excrete virus particles before they show symptoms. “We see a correlation between the sewer data and the number of reports of the GGD in the phase of growing infections,” says Medema. “So the more infections were reported by the GGD, the higher the RNA concentrations we found in the sewer in those places.”
Traces of the virus were found in the sewage water of Amersfoort and Terschelling six days before the first positive corona test. A week after the first confirmed infection in the Netherlands, the virus was already measured at more than half of the sewage treatment plants where measurements were taken.
“With the decrease in infections and hospital admissions, we see that the concentration of RNA particles is falling faster than the number of reports of the GGD,” says Medema. “The sewage water screening is a good reflection of society.”
Much faster than via test
Contamination can be measured after about two days via the sewer, while it takes almost two weeks via a corona test. That’s because the virus first has an incubation period of about five days. After that it often takes about a week before any complaints worsen and people report to the doctor. “That’s long for a virus that is spreading exponentially,” says Medema.
According to the microbiologist, the sewer measurements also provide much more information about an entire region. “Above ground, one test is needed for one person. In the sewer, one test is sufficient to determine early on whether the entire population is infected.”
As a result, a second wave comes to light more quickly. It is not yet possible to say how many people have been infected on the basis of the sewer measurements. Further research is being conducted into this.
Dashboard
At the press conference of Prime Minister Rutte and Minister De Jonge on 19 May, it was announced that the sewage water screening will also be part of the corona dashboard. With this, the cabinet wants to closely monitor whether the virus is resurrecting somewhere, now that the measures are increasingly relaxed.
The Ministry of VWS has asked RIVM to elaborate on this. There is now a pilot of weekly measurements at 29 sewage treatment plants spread across the Netherlands. The faeces of a quarter of the Dutch come in here.
RIVM will publish the research results in the second week of June. Then more will be known about the precise role of the sewage water screening in the corona dashboard.
Rotterdam research
In Rotterdam, an investigation is also being conducted into the relationship between the number of corona infections and the sewer measurements, carried out by virologist Marion Koopmans of the Erasmus MC. “Early recognition is crucial to prevent a second wave of the virus,” she says. “A significant proportion of corona patients excrete the virus through their faeces, even if they do not have any symptoms.”
In the study, Koopmans wants to clarify how many infections are behind a certain increase in the rna concentration. According to her, the sewage research will become increasingly important in the coming months, as fewer patients enter the hospital. “Many people who have the virus have no complaints. You don’t see them at the GP.”
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