A team from the Paris Seine Hospital Group in Saint-Denis wrote their findings in a study published Sunday in the International Journal of Antimicrobial Agents.
The first official reports of COVID-19 in France were reported on January 24 in two people with a travel history in Wuhan, China.
The researchers then decided to check the records of previous patients, in case the virus had spread without being detected.
The French team examined people admitted to hospital for flu-like illness between December 2 and January 16 who were ultimately not diagnosed with influenza. They tested frozen samples from these patients for coronavirus.
This patient was a 42 year old man born in Algeria, who lived in France for many years and worked as a fishmonger. The man had not been to China and one of his children was also sick.
His last trip was to Algeria in August 2019.
Europe only started reporting coronavirus cases in January. In Italy, the European country hardest hit by the virus, the first two cases were reported on January 31, among two Chinese tourists in Rome. The first known community transmission was recorded in late February in Codogno, in northern Italy.
American researchers have also started to find evidence that the virus infected and killed people earlier than the first cases reported in the country.
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