Sampling of wastewater at three facilities in Stockholm began in mid-April, after studies showed that remnants of the virus could be detected in sewage water, but this is the first time broad results have been published.
The researchers at the Royal Institute of Technology's (KTH) Water Centre said their method of taking virus measurements from wastewater meant their findings were not dependent on the level of testing for the novel coronavirus.
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“In the study we can conclude that we are seeing a clear increase in the number of cases of Covid-19, that isn't due to more people being tested,” Zeynep Cetecioglu Gurol, associate professor at KTH, said in a statement.
In recent weeks Sweden has seen a rise in cases, but the country is also conducting much more testing, making it difficult to determine how widespread the virus is now compared to earlier months.
For instance, in the last week of September, the country conducted some 129,000 PCR tests, compared to 36,500 tests in the last week of May.
The sewage water testing could help provide important insights into the spread and prevalence of the disease without the need for expensive widespread individual tests.
“This type of water analysis could definitely save resources for society, they give valuable information that can be combined with other parameters,” Cetecioglu Gurol said.
As of Friday, the most recent day for which data is available, Sweden had confirmed 94,283 cases of Covid-19 and 5,895 associated deaths.