The corona pandemic leaves its mark in the sewer

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Fortunately, the odor gradually diminishes as we climb the steel stairs, to the concrete top of a large round basin. “This is where the sewage from the wider area comes in,” explains Eric Langermans. He is a process operator at the sewage treatment plant (WWTP) in Den Bosch. Sewage is suddenly in the spotlight, he says. “Because it can contain coronavirus.”

A significant proportion of people who become infected with the pandemic virus SARS-CoV-2 excrete it through their feces. This is how it ends up in the sewage. In recent months, it has been in many countries – China, The Netherlands, Australia, Spain, Italy, United States – demonstrated with tests detecting hereditary material (RNA) from SARS-CoV-2. And now researchers are trying to find out whether you can set up reliable corona screening based on sewage water.

Is it possible, for example, to read from that water early whether the virus is spreading among the population and infecting more people? An important question now that several countries are easing their lockdown and there is fear that the virus will spread again. The Netherlands is also loosening further – from Monday, restaurants, cafes, cinemas, theaters will open again, and a day later also secondary schools.

Photo John van Hamond

On top of the basin, Langermans frowns, opening a cupboard with a ladle and a white jerry can. He is not following the investigation closely, he says. “I’m taking samples, that’s it.” With the ladle, he transfers stinky, brownish water from the jerry can into a milk bottle. “For every 300 cubic meters of water that flows into the basin, 50 ml is automatically drained, which is pumped upwards into this jerry can,” he explains. He fills a total of two milk bottles. He does this every six days, he says. “The bottles go into the refrigerator.” Until someone from RIVM comes to collect them.

At the RIVM in Bilthoven, Ana Maria de Roda Husman is positive about the potential of sewage water. She is head of the Environment department and wrote a short article (a correspondence) with colleague Willemijn Lodder about the first results of their research. It is published on April 1 in The Lancet Gastroenterology & Hepatology. They have been investigating sewage from Schiphol since 17 February. “Because it’s such a hub of international traffic, and you should quickly see if you’ve introduced corona from abroad,” says De Roda Husman.

Initially, they found no coronavirus. However, this was the case from 2 March. It was four days after the first Dutch case of Covid-19 was reported, the disease caused by the virus. But that was in Loon op Zand in Brabant, a completely different part of the Netherlands.

At that time, patients with Covid-19 were not known near Schiphol. It indicates, says De Roda Husman, that you also find virus in the sewage of the large group of people who do not get any complaints after infection. Or from people who are already infected and excrete the virus in their feces, but only get complaints later. In their correspondence, they write that detection of SARS-CoV-2 in sewage is one early warning tool could be. As RIVM has previously helped set up for the polio virus, for example.

Photo John van Hamond


Read about a previous sewage test: Syrian polio threatens Staphorst

You also want to see extinction

About the same time as RIVM, the water research institute KWR in Nieuwegein also started screening sewage water. Also at Schiphol and Tilburg, but also at Amsterdam, The Hague, Utrecht, Apeldoorn, Amersfoort. KWR also found coronavirus, in this case in Amersfoort, before cases of Covid-19 were reported there. “If one out of every 100,000 people has been reported to the GGD, we can already see it in sewage,” says research leader Gertjan Medema.

According to him, it is now clear that the virus can be detected early. But, he adds, you also want to know if “the signal corresponds to the disease.” In other words, if the virus spreads and makes more people sick, or vice versa, if the virus extinguishes, you also want to see it in the water. And that seems to be the case, says Medema.

Since a few weeks we have seen the signal decrease again

Gertjan Medema

With colleagues he published an article on May 20 in Environmental Science & Technology Letters. For the seven cities that they examined sewage, they compared the cumulative number of Covid-19 patients to the amount of virus they found – both logarithmic. And that adds up nicely. “We’ve seen the signal decrease again for a few weeks,” he says. This is consistent with the declining hospital admissions of the number of Covid-19 patients.

Most sewage tests for SARS-CoV-2 target the gene for the N protein (N stands for nucleocapsid). That protein fulfills several roles. It is attached to the inside of the membrane and holds the hereditary material (in this case rna) in place, but it is also important in the multiplication of the virus. More specifically, the tests focus on three parts of the N gene. In the laboratory, three pieces of DNA are added to the sewage, each encoding a different part of the N gene. If there is SARS-CoV-2 in the water, the added pieces bind to their complementary pieces of hereditary material of the virus.

Specifically, those bonded pieces are made using the pcr technique (polymerase chain reaction) so that the researchers get a clear “SARS-CoV-2” signal among all the other hereditary material of the myriad bacteria and viruses that are also in sewage. “The three parts of the N protein do not all send an equally sensitive signal,” says Medema. In their article, they conclude that more research is needed on the relationship between virus RNA in sewage and the number of people infected. Also, more data is needed per city, and more cities and towns need to be added.

Since 1 April, RIVM has expanded its research to 29 WWTPs out of a total of 352 in the Netherlands, says De Roda Husman. In addition to the provincial capitals (including Den Bosch), for example, there are also places where the GP stations that the RIVM follows to monitor the spread of the virus are located. For example, the selection of those 29 WWTPs also includes municipalities that have been severely affected, and others that have hardly had any cases of disease or corona deaths. In a few weeks, De Roda Husman expects to present the first results of the study.

Watch faster

But does a sewage test still offer an advantage if everyone with mild complaints can be tested from Monday 1 June? Medema thinks so. In their investigation, they sometimes found the virus in sewage 6 days earlier before the first Covid-19 report came. That was still in the period with a strict and limited testing policy. Now that anyone with mild symptoms can get tested, you will probably notice a new spread of the virus more quickly. “But anyone with mild complaints will also be tested,” Medema wonders. “And then there is still a large group of people who do not get any complaints.” De Roda Husman also sees it as an advantage that you monitor “almost all” infected people with the sewage test.

“Almost all,” she says, “because you miss those who wear diapers, babies, and some of the elderly.”

Other countries also have plans to introduce the sewage test. Or have already done that. Researchers from the University of Valencia have already set up an early detection system on behalf of the regional government. “In the region, we take samples from the three largest WWTPs twice a week to monitor the disease,” said Pilar Domingo-Calap, one of the coordinators of the Spanish study, by email.

There is now a European initiative, says Medema, to coordinate the monitoring of sewage water in a hundred cities and to compare tests. It is also being investigated whether you can zoom in further from an WWTP, if you pick up a corona signal. A WWTP receives sewage from often hundreds of thousands of people. “In Singapore and Istanbul, for example, people are looking into whether you can follow individual, often poorer neighborhoods further up the sewage network, where people are close together,” says Medema.

The disadvantage is that the signal becomes more unreliable. One person excretes a lot of virus in his stool, the other very little. “Those differences are reflected when you test a large population. But you can get big fluctuations at the neighborhood level. ”

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