The novel coronavirus was circulating in Italy since September 2019, a new study by the National Cancer Institute (INT) of the Italian city of Milan finds, three months before it was first reported in China.
In December 2019, cases of pneumonia of unknown cause were reported in central China's Wuhan City. The illness was later identified by the World Health Organization as COVID-19 caused by the coronavirus SARS-CoV-2.
But the new study adds to the possibility that the virus had originated and spread outside China earlier than widely thought.
Read more: Expert: Spotting COVID-19 first doesn't make China origin of virus
Italy's first COVID-19 patient was detected on February 21 in a little town near Milan, in the northern region of Lombardy.
But the Italian researchers' findings, published by the INT's scientific magazine Tumori Journal, show that 11.6 percent of the 959 healthy volunteers enrolled in a lung cancer screening trial between September 2019 and March 2020, had developed coronavirus antibodies well before February.
A further specific SARS-CoV-2 antibodies test was carried out by the University of Siena for the same research titled "Unexpected detection of SARS-CoV-2 antibodies in the pre-pandemic period in Italy."
It showed that four cases dated back to the first week of October were also positive for antibodies neutralizing the virus, meaning they had got infected in September, Giovanni Apolone, a co-author of the study, told Reuters.
"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," Apolone said.
"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," he added.
Italian researchers told Reuters in March that they reported a higher than usual number of cases of severe pneumonia and flu in Lombardy in the last quarter of 2019 in a sign that the new coronavirus might have circulated earlier than previously thought.