Since the end of February, KWR has been monitoring concentrations of the genetic material of the coronavirus, so-called SARS-COV-2 RNA, in the sewage water in seven cities, at Schiphol Airport and in Terschelling. The concentration is a measure of the infection rate among the population that is connected to the analysed sewage system. The KWR microbiologists were one of the first research groups in the world to publish their research method, so that colleagues in other countries could also monitor sewage water in a standardised fashion. This page presents the current analysis of the sewage water samples collected on Thursday, 20 August.
We do not observe any great shifts in Amsterdam, Utrecht, Amersfoort, Tilburg, Schiphol or Franeker. Rotterdam, in turn, shows an increase for the second week in a row. In Apeldoorn, a signal can again be observed for the first time after a long period, and Terschelling has again fallen below the detection limit. We did not receive any monitoring data for The Hague.
Sewage water samples of 20 August
After two weeks of increases in Amsterdam a slight decrease can again be observed. Next week we will be able to see whether the general rising trend continues or whether the curve drops once more.
The concentration in Utrecht is fluctuating; the trend is slightly decreasing.
After a sharp rise in Amersfoort last week, there is now a slight decrease.
In Tilburg, for the second time in a row, no signals were observed.
The monitoring data for the last week for Den Haag are not available.
At Schiphol we observe a slight rise, but the concentration remains at the same order of magnitude of the previous weeks.
The temporary population of Schiphol
Researcher Frederic Béen: ‘The sewage water data from Schiphol are relevant because they provide information about the circulation of the virus among people travelling through one of the key entry points to our country and the European continent. On the other hand, such a temporary “population” confronts us with sudden increases or decreases in the amount of genetic material (RNA) that is detected as a result of the presence of one or several infected passengers (or even ground staff and flight crew). As I said, monitoring the presence of SARS-CoV-2 in the wastewater stream at Schiphol is still very relevant. Now that air traffic is again increasing, our sewage water analysis provides an indication of whether the virus in entering the Netherlands through air travel.’
Following two weeks of a rising signal, the RNA level this week at Terschelling again dropped below the detection limit. We do not have either the number of cases reported to the Municipal Health Authority nor the number of hospitalizations for Terschelling.
As was the case the previous week, the signal in Franeker was under the detection limit. For Franeker as well, we only have the N2 gene fragments.
In Rotterdam (Dokhaven wastewater treatment plant) the concentration has risen again.
After nine weeks with no signal, we have again detected RNA from SARS-CoV-2 in the wastewater in Apeldoorn.
Keep a close eye on the curves
The increase of the SARS-CoV-2 RNA concentration in the sewage at the beginning of the first COVID-19 wave was, in that phase, an indication for a later increase in the number of hospitalizations. It is reasonable to assume that something like this will also apply to a second wave. But there is a difference between the first and second waves. In the first wave the virus (RNA) was completely absent beforehand. Now, the virus (RNA) is still present in the sewage. This is why it is now important to keep a close eye on local increases. By seeing whether the RNA concentrations are constantly rising, and by comparing the sewage data with the other information sources: the Municipal Health Authority reports and the hospitalizations. For Gertjan Medema ‘none of these data sources is perfect, but, together, they provide a more complete picture of the circulation of the virus.’
Early warning system
Based on regular monitoring, we have observed the evolution of curves since the beginning of the corona crisis at different locations. The curves correlate with the number of registrations at the Municipal Health Authorities and with the number of hospitalizations. It is striking that the sewage water curve ‘reacts’ approximately one week before the other two. This is not so surprising, since people contaminated with the coronavirus have no symptoms during the first few days following infection, but they do excrete the virus in their faeces. Into the sewage. That makes the sewage an early warning system.
From the beginning of March, the curves began to rise rapidly. At the end of March a peak could be observed in most places, and in early April a decline began. In the month of June, we saw that the concentration of virus fragments in a number of cities fell below the so-called detection limit. In other words, the state-of-the-art measuring equipment at KWR could not detect the presence of any SARS-COV-2 RNA in the sewage water sample. Now that the number of infections in the Netherlands is again increasing, the sewage water data allow us to provide an additional basis for regional/local government corona measures.