The World Health Organization (WHO) says it is possible more countries could find out they had positive cases of COVID-19 much earlier than previously thought.

It comes after a doctor in France revealed retrospective samples show the coronavirus was already present there in late December 2019.

Christian Lindmeier, a spokesperson for the WHO, said: "The findings, now in France, or in any similar scenario, help to better understand the potential virus circulation of COVID-19."

It's not surprising, given the earliest confirmed sufferers of COVID-19 had onset symptoms already in early December.

"So it's possible that some of these infected people traveled from Wuhan to other countries at that time."

On 31 December last year, China alerted the World Health Organization to several cases of unusual pneumonia in the city of Wuhan. By that time it now seems the then-unknown virus could already have been circulating thousands of miles away in Europe.

A French hospital, which retested old samples, found that one patient had COVID-19 as early as 27 December – nearly a month before the first cases in the country were officially confirmed.

That patient in France says he was admitted to hospital for what he thought he was a serious case of the flu.

But Amirouche Hammar has told French media he was told at the time that what he had was "very serious flu."

He also says he was suffering from "severe chest pain… and gasping for air."

There are no reasons to believe France could be an isolated case. It's possible more cases could be found as more countries retest old samples from patients who were sick in December or January.

"The Chinese outbreak was handled very, very well, once it was recognized how serious this was," says Ian Jones, a professor at the University of Reading, in the UK.

"But there is some genuine concern around the early few days, around the seafood market in Wuhan, whether or not the early cases of pneumonia were considered to be serious or whether they were just considered to be routine and not worthy of being followed up."

Video editor: Natalia Luz

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