With coronavirus found in water systems, is it safe to swim this summer?

Microbiologist Laurent Moulin and his team at French public water authority Eau De Paris have been studying viruses transmitted by water for more than a decade. So when the Covid-19 outbreak began earlier this year they decided to track the virus, known as SARS-CoV-2, in wastewater treatment centres.

Moulin admits some people might find it surprising that a respiratory virus has been identified in faeces, but in fact traces are often found before patients have symptoms.

The team's research revealed that the amount of virus present in the sewage correlated with the number of people presenting with Covid-19 in that geographical area.

"This data is useful for health authorities because it allows them to make decisions. In the case of a hypothetical second wave, it would make it possible to detect an increase in the number of patients, the number of sick people, and then monitor an epidemic outbreak," Moulin explains.

These findings have prompted other scientists to investigate whether the virus may have spread more widely into the natural environment, particularly along the coast. In the past, other viruses, such as the ones responsible for gastroenteritis, have bypassed treatment facilities and infected entire beaches. 

The best way to measure concentrations of the SARS-CoV-2 virus in the sea is with shellfish. 

Soizick Le Guyader, a virologist with the French Research Institute for Exploitation of the Sea, is conducting regular tests on oysters across 24 sites in France.  

Oysters act like a filter, incorporating contamination that may be present in the seawater.

For the moment three sets of samples have been negative, meaning there are no signs of the virus and it is safe to swim.

But Le Guyader warns: "What's important now is to see how easing lockdown impacts the spread of the virus, especially with summer arriving and people heading to the coast. So let's stay alert."