Shortly before Christmas there is coughing and sniffling in every corner. In many doctor’s offices the waiting room is full. According to the current weekly report from the Robert Koch Institute (RKI), 7.9 million people in Germany are currently suffering from a respiratory infection. But how many corona infections are there?
During the pandemic years, people tested diligently at home, in doctor’s offices or test centers to find out whether a sore throat, runny nose and fever were due to a cold or whether they had been infected with the coronavirus. The positive rapid test still had to be confirmed with a PCR test and the family doctor’s practice reported the case. The RKI had a good overview of the number of corona infected people.
A look at the corona pandemic radar reveals that the current 7-day incidence of reported cases is 38 (as of December 15, 2023). As a reminder: The 7-day incidence provides information about how many people per 100,000 inhabitants have contracted Covid-19 in the last seven days. At the height of the Omicron wave in spring 2022, the 7-day incidence was almost 2,000. The raw numbers read as if almost no one in Germany was currently infected with Covid-19. But it is not that simple.
The situation is different today. We can voluntarily do a corona test at home. Systematic testing is only carried out in hospitals for symptomatic patients. So that means: The 7-day incidence from 2022 and today cannot be compared. In order to better assess the situation of Covid-19 infections, the RKI is now using other methods. On the one hand, the RKI uses information from flu web participants to assess the corona situation. According to the current weekly report, the estimated 7-day incidence is 2,500 corona infections per 100,000 inhabitants. For the estimates, the RKI also uses the findings of the SentiSurv study at the Mainz University Medical Center. For this purpose, 10,000 representatively selected adults from Rhineland-Palatinate test themselves once a week. SentiSurv comes to a 7-day incidence of 3,896 in Rhineland-Palatinate in the week ending December 13th.
On the other hand, the viral load in the wastewater is measured. The viral load, with an average of almost one million gene copies in one liter of water, has reached its highest level since measurements began in June 2022. The latest data in the corona pandemic radar lasts until November 29th (as of December 12th, 2023). Wastewater monitoring is an important means of identifying trends in the Corona situation. Because: As described, scientists can no longer rely on the 7-day incidence as much as they did when testing was mandatory. The wastewater monitoring data shows that the viral load in wastewater has been increasing since the end of June 2023. So a trend can be seen.
But where does the data in wastewater monitoring actually come from? The RKI currently receives data from 82 sewage treatment plants in Germany. However, these are not selected representatively. If a person is infected with Sars-CoV-2, he or she excretes the pathogen through stool, urine or saliva. By taking samples from wastewater from sewage treatment plants, scientists can evaluate how high the viral load is per liter of water. To do this, the sample is prepared in the laboratory and the coronavirus is detected using a PCR test. Monitoring the coronavirus in water is a supplementary measure to better assess the corona situation. Wastewater monitoring provides information on viral load and infection dynamics.
However, it is not possible to determine exactly how many people are sick with Covid-19. Infected people sometimes excrete more and sometimes less viruses – depending on which variant they were infected with or how long they have had the infection. It is also not possible to determine the severity of the infection or the burden on the health system. This means: The data from wastewater monitoring is merely a supplement. In addition to Sars-CoV-2, other diseases could also be better monitored in the future with such monitoring.
Sources: RKI weekly report, RKI FAQ, Pandemic Radar 1, Pandemic Radar 2, SentiSurv study
