Coronavirus was present in Italy months before its outbreak is known to have started, according to new research.
Scientists have found Covid-19 antibodies in blood samples from as early as September last year.
The findings “may reshape the history of the pandemic”, they said.
Italy reported its first coronavirus cases in late January, after which an outbreak swept through the country, hitting northern areas such as the Lombardy region particularly hard.
Traces of coronavirus have also shown up in Italy’s water from December last year – suggesting the virus was circulating more than a month before the country’s first confirmed infection.
However, new findings have suggested the virus was present in the country even earlier.
Scientists analysed blood samples of nearly 1,000 people – all asymptomatic – who had taken part in a lung cancer screening trial running from September 2019 to the following March.
Covid-19 antibodies were discovered in around 11 per cent of those studied, according to the research published in Tumori Journal.
Fourteen per cent of those detected were from September last year, and around 30 per cent were from the second week of February, the group of scientists – including several from Fondazione IRCCS Istituto Nazionale dei Tumori, a leading cancer research centre – said.
“This study shows an unexpected very early circulation of SARS-CoV-2 among asymptomatic individuals in Italy several months before the first patient was identified,” the researchers wrote.
They said it “clarifies the onset and spread of the coronavirus disease 2019 (Covid-19) pandemic”.
Elsewhere in Europe, other studies have found coronavirus to have been present before an outbreak was confirmed.
In May, a hospital in France said it had treated someone with Covid-19 around a month before the first cases were officially reported in Europe.
They discovered they had looked after a man who was positive for coronavirus in late December after retesting old samples from pneumonia patients.