A medical worker uses a swab to take a sample at a COVID-19 drive-thru testing site in Washington DC, the United States, on April 28, 2020. (TING SHEN / XINHUA)

A public official in the United States and another man in France could have been infected with the novel coronavirus months before cases were reported in the two countries.

It's also possible there are more early cases to be found.

Christian Lindmeier, WHO spokesman

Michael Melham, who is the mayor of Belleville, New Jersey, said he tested positive for coronavirus antibodies and believes he was sickened in November, which would mean his case could be the earliest reported in the United States, according to a local news report.

The earliest official US case, which was announced by the Centers for Disease Control and Prevention on Jan 21, was of a man who had returned to the Seattle area after visiting Wuhan, China, where the virus was first reported.

In France, researchers led by Yves Cohen, head of resuscitation at the Avicenne and Jean Verdier hospitals, retested samples from 24 patients treated in December and January who had tested negative for influenza before COVID-19 had developed into a pandemic.

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Their findings, published in the International Journal of Antimicrobial Agents, showed that one patient－a 42-year-old man born in Algeria who had lived in France for many years and worked as a fish seller－was infected with the coronavirus "one month before the first reported cases in our country", the researchers said.

The World Health Organization, or WHO, said the results in France were "not surprising".

WHO spokesman Christian Lindmeier told a United Nations briefing in Geneva: "It's also possible there are more early cases to be found." And he encouraged other countries to check records for cases in late 2019, saying it would give the world a "new and clearer picture" of the outbreak.

Results received in April

Melham became sick with chills, hallucinations and a high temperature after he left the three-day League of Municipalities Conference in Atlantic City on Nov 21, according to northjersey.com.

A doctor told Melham that he had the flu and would recover. He eventually asked his doctor for a coronavirus antibody test and received the results on April 29.

"The antibody in my blood is older as opposed to the more recent one showing you just finished fighting it off," Melham said.

Melham also expressed doubts about when the virus arrived in the US.

"I have never believed this just came in January. I know many people like me who were gravely ill from November into December," he told another website, nj.com.

In France, BFM TV identified the early coronavirus patient as Amirouche Hammar, a resident of Bobigny, a Paris suburb. In an interview with the station, Hammar said that when he became ill last year with a dry cough, fatigue and a fever, he thought he had the flu.

Hammar's wife works at a retailer near a Paris airport and comes into contact with overseas travelers.

"It's not impossible that it was an early introduction, but the evidence isn't conclusive by any means," said Jonathan Ball, a professor of molecular virology at the University of Nottingham in England.

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Meanwhile, the researcher Cohen told French television on Monday that it was too soon to tell if Hammar, whose last trip abroad was to Algeria in August 2019, was France's "patient zero".

But "identifying the first infected patient is of great epidemiological interest as it changes dramatically our knowledge regarding SARS-COV-2 and its spread in the country", he and his co-researchers wrote.

They said the absence of a link with China and the lack of recent travel "suggest that the disease was already spreading among the French population at the end of December 2019".

Agencies via Xinhua contributed to this story.