Very early in the pandemic, scientists discovered that infected people “shed” the virus in their faeces. Small studies conducted by teams in the Netherlands, France, Australia and elsewhere have found signs that the virus that causes COVID-19 can be detected in sewage, and many countries are beginning to use wastewater sampling to track the spread of the disease.
Scientists in Italy found traces of the new coronavirus in wastewater collected from Milan and Turin in December 2019 – suggesting COVID-19 was already circulating in Northern Italy before China reported the first cases. The Italian National Institute of Health looked at 40 sewage samples collected from wastewater treatment plants in northern Italy between October 2019 and February 2020. An analysis released late on Thursday said samples taken in Milan and Turin on Dec. 18 showed the presence of the SARS-Cov-2 virus.
Sewage testing is being conducted across England in a bid to develop wastewater-based Covid-19 surveillance. Further research concluded that analysing sewage could help scientists predict a second peak of Covid-19 up to two weeks before people become symptomatic. The Department for the Environment, Food and Rural Affairs says this has begun at 44 wastewater treatment sites, and the government is working with scientists, water companies and the devolved governments in Scotland, Wales and Northern Ireland.
In Wales, a team from Bangor University has been looking at samples from water treatment works across the country in a bid to trace how many people have been infected. The team has previously tracked norovirus through the sewage system. People start to shed the virus in faeces up to two weeks before the onset of symptoms.
Professor Davey Jones said it was an effective method for tracing viruses partly because it is possible to capture data on the majority of the population in a relatively cheap and simple way. “We want to understand where and when Covid-19 infections are occurring within Wales,” he said. “So far what we’ve shown is that in north-west Wales the number of virus particles in the sewage is really, really low, suggesting there is almost no Covid-19 circulating in the population.
“In contrast in north-east Wales and south-east Wales the numbers of Covid-19 virus in waste water are really, really high suggesting they are infection hot spots at the moment.” He said the findings were in line with what they were expecting, given the numbers of confirmed cases in Wales. “It’s important to understand how many cases we have in the country, but it’s also important to understand how many asymptomatic carriers that we have,” he said. “Those are the people who might have very mild symptoms or no symptoms at all. It could be that they are an important source of infection within the community.”
There are problems to be solved in order to maximise the accuracy and value of a sewage-based surveillance system: the propensity of the virus to break up when it is in water; the effect on the result of other contaminants; and how many sampling points need to be included in a UK-wide network in order to build up a useful picture of the outbreak.