When Barcelona, Spain, started analysing waste water samples from 2018 to 2019 they found Covid-19 present in the samples a year before the pandemic.

"A study led by the University of Barcelona (UB) has detected the presence of SARS-CoV-2 in wastewater samples from Barcelona on March 12, 2019. 

The results of the research, published on the medical research website medRxiv, would indicate that the virus was present long before any case of Covid-19 was discovered, the university reports. 

The research is part of a project on the coronavirus that aims to detect it in wastewater to facilitate the adoption of early measures. The results come from the analysis of frozen samples, showing the virus present in the water on January 15 this year but also in a sample from March 2019, although at "very low" levels.

Although Covid-19 is a respiratory disease, it has been shown that there are large amounts of the coronavirus genome in feces, which subsequently reach wastewater. This makes wastewater-based epidemiology a potential tool for early warning of virus circulation in the population, especially important given the numbers of asymptomatic or presymptomatic people.

Since 13 April, researchers have been analyzing samples obtained at two large wastewater treatment plants in Barcelona. The professor of the Faculty of Biology at the UB and coordinator of the work, Albert Bosch, explained that the levels of the genome of SARS-CoV-2 coincided "clearly" with the evolution of confirmed cases of Covid-19 in the population.

Subsequently, the researchers analyzed frozen samples from the months prior to the confirmation of cases among citizens. These analyses revealed the growing appearance of SARS-CoV-2 genomes between early January and early March this year, advancing the chronology of the arrival of the coronavirus in Spain. "

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