Given the small number of patients who show gastrointestinal symptoms, researchers wonder if the coronavirus that causes Covid-19 is present in sewage. And it has been found in several wastewater treatment plants in the Netherlands.
Covid-19 is a disease that mainly affects the respiratory system. However, several studies have reported gastrointestinal symptoms in a minority of patients. In some cases, SARS-CoV-2 coronavirus has been detected in rectal samples.
It remains unclear how the virus reaches the gastrointestinal tract. However, the famous cell receptor ACE2, used by coronaviruses during infection, is known to be abundantly expressed in intestinal epithelial cells. Mainly in people who are infected with SARS-CoV-2 but do not show any symptoms, excretion of the virus in the stool may be involved in the transmission of the virus.
Several research groups are investigating the presence of coronavirus in sewage at wastewater treatment plants. So far, researchers have found traces of SARS-CoV-2, in the form of viral RNA, in several countries, including the Netherlands.
Estimation of the spread of the virus in the population
According to Dutch microbiologist Gertjan Medema, monitoring the contamination of sewage collected from wastewater treatment plants can provide a more accurate estimate of the spread of the virus than traditional testing, since it takes into account untested or asymptomatic but infectious individuals.
However, at present it is difficult to draw conclusions: data on fecal excretion of SARS-CoV-2 are lacking. Researchers would need to know the amount of virus present in the feces to estimate the amount found in the wastewater.
Early detection of outbreaks
The detection of a virus in the wastewater also acts as an alarm signal. According to Nature, the research group that analyzed the effluent from Schiphol airport identified SARS-CoV-2 four days before the first case was confirmed based on clinical signs. This analysis was repeated in 12 major cities in the Netherlands, some of which did not report cases. Before the first case was reported, the wastewater from Amersfoort tested positive.
According to the journal Nature, studies have shown that the virus is excreted in the feces within three days of infection, well before the first symptoms appear. Surveillance of sewage could allow for preventive measures to be administered much earlier than with traditional testing. Virologist Tamar Kohn of the Swiss Federal Institute of Technology in Lausanne (EPFL) says: “Seven to ten days can make a big difference in the severity of this epidemic.”