It is conceivable that undetected coronavirus infections could be source of new outbreaks, making Covid-19 difficult to control. In fact, the pandemic grew in a non-controlled way because of the “stealth transmission”: at the beginning, the first few symptomatic cases were treated as normal pneumonia, while the majority of people carrying the virus were non-symptomatic. Still, it is believed that most people with Covid-19 do not bear any relevant symptoms, although they are able to spread the disease. The only way to control the pandemic is to isolate all the infected people, but this is a “mission impossible” (not even Tom Cruise would be of any help, unfortunately): it is unthinkable to test everyone, also because the test should be run periodically. Moreover, it is unlikely that the disease will disappear after this health crisis. So what to do? An unexpected help might come from… sewage. Yup, I’m serious: scientists are already working on it and it is a pretty smart idea. Testing wastewater (the water that goes through the drainage system to a treatment facility) would give a first relevant indication of a new outbreak in its early days. Analysing wastewater has several advantages:
- Time. While the Covid-19 could be asymptomatic for up to two weeks, virus is detected in faeces after three days of infection. This would save 10 days of waiting, which is a crucial time in limiting the spreading of a pandemic, as we painfully learnt.
- Regular monitoring. A test on wastewater can be run periodically and any increase of viral presence would be quickly detected.
- Stealth infections. Treatment facilities collect wastewaters from millions of people, therefore the test would provide information on the thousands of asymptomatic, but infected individuals.
Before running wastewater tests efficiently, some information needs to be collected. For example, a precise estimate of the virus amount in faeces has to be calculated. This will allow to approximate how many people are infected, depending on the amount of virus measured in the sewage. Moreover, the sensitivity of the test has to be established and it is important that the virus is detected also at low level, to catch the outbreak at the beginning. In the Netherlands, researchers could detect the virus SARS-CoV-2 in the sewage of Amsterdam Schipol Airport only four days after the first coronavirus case was confirmed in the country.
Worldwide, sewage testing has been already employed successfully to assess the presence of norovirus, antibiotic-resistant bacteria, poliovirus and measles spreading. It is important to mention that it’s not proposed as an alternative to individual testing, which won’t be replaced, but as a relevant implementation of the surveillance strategy.