Coronavirus was circulating in Italy as early as September 2019, scientists there have claimed.
The World Health Organization says COVID-19 was unknown before the outbreak was first reported in Wuhan, in central China, in December. A few months later, the first official cases were detected in Europe.
However, scientists in Italy say they have found evidence the virus was circulating much sooner by checking blood samples of patients taking part in a cancer study.
Samples from four patients, dating back to the start of October 2019, were found to contain antibodies, according to findings published by Milan's National Cancer Institute (NCI).
The results mean they would have caught coronavirus in September - some five months before Italy recorded its first official COVID-19 patient on 21 February, in a town near Milan, in the northern region of Lombardy.
The study - published by NCI's scientific magazine Tumori Journal - found that 11.6% of blood samples from 959 healthy volunteers, who were enrolled in a lung cancer screening trial between September 2019 and March 2020, had developed antibodies well before February.
Giovanni Apolone, a co-author of the study, which has not been peer-reviewed, said: "This is the main finding: people with no symptoms not only were positive after the serological tests, but had also antibodies able to kill the virus.
"It means that the new coronavirus can circulate among the population for long and with a low rate of lethality not because it is disappearing but only to surge again."
A further specific SARS-CoV-2 (the coronavirus strain that causes COVID-19) antibodies test was carried out by the University of Siena for the same research.
Previously, Italian researchers have said that they reported a higher than usual number of cases of severe pneumonia and flu in Lombardy in the last quarter of 2019 - a sign the new coronavirus might have been present.
The virus is surging again, with the Italian health ministry reporting on Sunday that there had been another 33,979 new infections over the past 24 hours - down from 37,255 on Saturday.
There were another 546 COVID-related deaths, up from 544 the day before.
Lombardy remained the hardest hit area on Sunday, reporting 8,060 new cases against 8,129 on Saturday.
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