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The coronavirus could have been present in Barcelona a year before the pandemic - and if so, that probably means it was present in other places long before anyone had heard of it, too. Researchers at the University of Barcelona (UB) have detected the presence of SARS-CoV-2 in sewage samples collected in Barcelona on March 12th, 2019. This means that, if confirmed by peer review, the virus was present one year before the coronavirus pandemic was declared at global scale (March 11th, 2020) and the state of alarm was declared in Spain (March 14th, 2020). 

Tweet from the University of Barcelona research group, linking to the study in English

The presence of the coronavirus in Barcelona in early 2019 is a "striking finding" which would mean that the infection was circulating well before it became known, according to the study. In fact, it could complete upturn the theories on the origin and spread of the virus. 

Why might the Covid-19 have been found in Barcelona at this time? "Barcelona is a business and commerce hub, as well as a popular venue for massive events, gathering visitors from many parts of the world," says the UB study, adding that "it is nevertheless likely that similar situations may have occurred in several other parts of the world, with circulation of unnoticed COVID-19 cases in the community." 

Frozen sewage samples

Although Covid-19 is a respiratory disease, it has been shown that large amounts of the coronavirus genome are found in feces, which subsequently reach wastewater.

This circumstance has made wastewater-based epidemiology a potential tool for early warning of virus circulation in the population, especially given the significant presence of asymptomatic and presymptomatic people who also transmit it.

Due to the possibility that early cases were misdiagnosed, the UB researchers analyzed frozen samples of Barcelona's wastewater, going back to 2018. As well as the surprising positive result on March 12th, 2019 - achieved in two test procedures - their studies revealed that the virus was present on an ongoing basis in Barcelona from January 15th 2020, 41 days before the declaration of the first case of Covid-19 in the city​.

“Covid-19 infected people may have been erroneously assigned as diagnoses of influenza in primary care, contributing to community transmission before take public health measures," said Albert Bosch, also president of the Spanish Society of Virology. "In the specific case of Barcelona," the virologist continues, "having detected the spread of SARS-CoV-2 a month in advance would have allowed a better response to the pandemic."

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