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Corona in wastewater reaches third-wave peak

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Concentrations of coronavirus in Gothenburg wastewater have shot up in just a week. They are now on a par with the top reading during the third wave of the pandemic, in spring 2021, University of Gothenburg researchers have found.

“I hadn’t expected this — that there’d suddenly be such a rapid increase,” says Heléne Norder, adjunct professor of microbiology at the Department of Infectious Diseases at Sahlgrenska Academy, University of Gothenburg, and microbiologist at Sahlgrenska University Hospital.

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Heléne Norder, Institute of Biomedicine, Sahlgrenska Academy, University of Gothenburg.
Photo: Elin Lindström

The wastewater samples on which the survey results in question were based were taken last week, December 20th–26th. As far as can be judged, the majority of people who were then excreting the SARS-CoV-2 virus became infected at the beginning of that week or during the week before.

May affect care services

The sharp upturn that is now evident is the largest in a single week since New Year 2020, when the second wave of the pandemic was underway. The level, as such, corresponds to the peak reading obtained for SARS-CoV-2 in the wastewater of the Gothenburg area during the pandemic’s third wave, in late March.

During the pandemic a rise in virus concentrations in wastewater, showing increased prevalence of COVID-19 in the community, has been a way of predicting workload peaks in health care to various degrees. Norder continuously reports her results to care providers and the Infection Control Unit in Region Västra Götaland.

“It’s hard to be sure what this means, and what’s going to happen. I really hope that the people now excreting virus have been vaccinated. Then not so many will have to go into intensive care, or even be hospitalized, and can probably cope on their own at home,” Norder says.

The proportions of the two main variants, delta and omicron, in the past week have not yet been fully analyzed. The analysis for the preceding week showed a distribution of 50–50.

More norovirus

The surveys of SARS-CoV-2 in wastewater have been carried out since February 2020, in collaboration with the municipally owned company Gryaab. Every week this company, which treats wastewater in Gothenburg and the surrounding municipalities, sends the scientists a sample composed of samples collected daily.

Besides SARS-CoV-2, the investigations include concentrations of three other types of virus: Influenza A and B; norovirus, which causes the "winter vomiting bug"; and the respiratory syncytial virus (RSV), which infects the airway and can make small children seriously ill.

The past week’s analysis shows concentrations of norovirus rising slightly, Influenza A declining and RSV at very low levels.