How to detect coronavirus in wastewater | free Press

Chopsticks in the nose or throat: Testing is not the only way to find out how widespread Sars-CoV-2 is. From the experts’ point of view, sewage treatment plants could also serve as an early warning.

Berlin.

Relatively low cost, little effort, and a real-time picture of the pandemic situation: medical officials recently advocated expanding wastewater analyzes to include traces of the coronavirus. “It would be ideal if all the municipalities were to participate,” said the president of the Federal Association of Doctors in the Public Health Service, Johannes Nießen, of the Funke media group. So far, a pilot project is running in Germany with 20 locations, including Berlin. Questions and answers about it.

How do such surveys work?

First, wastewater samples are taken at the wastewater treatment plant. “Small bottles of 200 milliliters twice a week are enough,” said Emanuel Wyler, who has been analyzing virus variants at the Max Delbrück Center for Molecular Medicine in Berlin since early 2021. The sewage contains highly diluted microscopic components of the virus. that some infected people excrete when they brush their teeth or use the toilet. “We extract the viruses from the sample and then do a PCR test, just like with nose or throat swabs.” The sample is not only tested for Sars-Cov-2, but also for harmless but widespread plant viruses for comparability.

What can wastewater analyzes achieve?

The advantages are the lead time compared to official pandemic data and the independence from the number of tests (PCR) performed. In short, while only some people get tested, everyone has to go to the bathroom. According to experts, with sewage you are closer to real infections because infected people excrete viruses even before the onset of illness. The number of reports, on the other hand, lags behind the actual progression because of the time from infection to disease onset to PCR result and reporting to the Robert Koch Institute (RKI).

Information on lead time compared to RKI curves varies: while the head of the laboratory at the Berliner Wasserbetriebe spoke of seven days in an interview, for example, the city of Cologne gave a lead of four to ten days in a statement. Virus variants can also be detected with additional tests. According to experts, it is also technically possible to take a close look at places of special interest such as large companies or airports.

“Wastewater monitoring can show developments over time quite well and can also help identify hotspots, depending on how small-scale it is,” says Bremen epidemiologist Hajo Zeeb. In this respect, it is a “valuable addition” – also because it provides information quickly at best.

What does such an approach cost?

According to the Berliner Wasserbetriebe, a Sars-CoV-2 detection test costs around 300 euros. Determining the variant costs another 200 euros. “We bought a digital PCR machine and hired a microbiologist,” a spokesman said. Part of the analysis will be outsourced to an external laboratory. “Many smaller water suppliers, particularly without their own laboratories, should certainly go this way,” the spokesman said.

The German Association for Water, Wastewater and Waste Management (DWA) estimates an annual cost of €14 million if the 235 largest sewage treatment plants in Germany are included – this covers around half the population. Researcher Wyler also does not need to have samples from every municipality. “It would be too expensive.” Instead, samples from the 100 largest wastewater treatment plants in Germany are sufficient. “If you sampled there twice a week, you’d end up with a weekly cost of several tens of thousands of euros.”

Is wastewater testing worth it?

This should also be one of the questions in the ongoing pilot project. According to the description, this is intended to determine, among other things, how concepts developed so far for local contexts can be transferred to other regions. It is scheduled to run until March 2023.

For Wyler, the big question is what to do with the knowledge that a site is exploding or the next wave is approaching. In the event of a development, for example, will more people be sent to work from home again? Do you enforce a mask requirement or is a hospital proactively issuing a holiday ban? “Politics must answer this.”

Wyler also points out that wastewater values ​​do not provide information about disease severity and only show trends in the infection process. It is not possible to draw conclusions about the number of people currently infected in the population. According to the researchers, a certain amount of contamination is also required to be able to detect the virus in the wastewater.

What standards are there?

In many countries, wastewater is tested for Sars-CoV-2 in smaller projects or during larger investigations. In neighboring countries, such as Austria and the Netherlands, online corona control tables show the results. Local information is also available. The idea itself is not new: the analysis of wastewater for polio has been carried out in some countries for many years. In this way, insights into drug use in cities can also be gained. In addition to the corona, scientists are also interested in other pathogens, such as influenza and antibiotic-resistant bacteria. (dpa)

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