The health department and the cantonal laboratory cannot yet explain exactly why this decline has occurred. The analyzes and controls of the wastewater went normally, the health department announced on Friday at the request of the Keystone-SDA news agency.
It is possible that a lot of people are simply not at work or not at home over the holidays. If this hypothesis is correct, the values should rise again. “We will probably be able to draw further and more reliable conclusions in the course of the next week.”
No daily developments can be read out of the wastewater data, the development over several weeks must be taken into account: “Municipal wastewater is a complex matter and its composition changes constantly,” says the wastewater monitoring system on the website of the Eawag water research institute developed by the EPFL in Lausanne. For example, heavy rains could have an impact.
According to the situation bulletin, which the health department often reports daily in the late afternoon, more and more traces of corona are found in Zurich wastewater from the end of November to mid-December.
The highest level of the seven-day mean reached in this process clearly exceeded the peak values from mid-August, which were recorded at the end of the summer vacation. But then the values collapsed; in the latest bulletin they are back to the end of November.
The picture is different in the Zurich test centers. The seven-day mean of those who tested positive per 100,000 people fell slightly from around 100 to 90 for a few days before Christmas, but it has risen again since then and has now reached the 120 mark. That corresponds to a new high.
In absolute terms, too, new highs were reached in December. On December 24th, more than 2000 new positive corona cases were reported for the first time and in the last few days three between 2,394 and 2,552 newly confirmed infections were registered in the canton of Zurich.
Positive balance of wastewater monitoring
Since the end of May 2021, samples have been taken in twelve Zurich wastewater treatment plants and examined for genetic material of the Sars-CoV-2 virus. The virus concentration determined is intended to trace the development of the pandemic. According to the information provided by the health department, this wastewater measurement is running flawlessly.
“The data are another tool for observing the epidemiological situation from a slightly different point of view,” the management continues on request. So far it can be seen that the wastewater data could represent the data of the tests well. “This is important because it gives us an instrument that can measure the epidemiological situation independently of the test behavior of the population.”