ABOVE: One of the hospitals where Yves Cohen works.

A man living in France may have been infected with SARS-CoV-2, the virus that causes COVID-19, as early as December 27, weeks before the first official coronavirus cases were reported in the country, according to a study published online Sunday (May 3) in the International Journal of Antimicrobial Agents.

When the man, Amirouche Hammar, a 42-year-old fishmonger, visited a hospital north of Paris on December 27, he suffered from chest pains and had difficulty breathing. Doctors diagnosed him with viral pneumonia and treated him with antibiotics. “We told ourselves, ‘It’s a virus that we haven’t discovered,’ but we stopped there,” Yves Cohen, one of Hammar’s doctors who works at Avicenne and Jean Verdier hospitals, told BFM-TV, according to the Associated Press.

As cases of COVID-19 spread worldwide, Cohen and his colleagues decided to analyze samples taken from patients visiting the hospital who were diagnosed with influenza-like illness between December 2, 2019, and January 16, 2020. Of the 14 samples described in the study, only one, Hammar’s, was positive for SARS-CoV-2. Cohen and his team called Hammar after they got this result and learned he had not traveled before getting sick and that one of his children had fallen ill with similar symptoms around the same time. Both Hammar’s children ended up becoming sick while his wife showed no symptoms of illness. Hammar’s wife worked in a local market selling fish. She may have been an asymptomatic carrier, contracting the virus at the market, Cohen tells BF-MTV.

Cohen and his colleagues caution that the work is tentative. The study was done retrospectively, “medical records were not exhaustive and some relevant information might have been missing,” Cohen tells the AP.

The sample could also have been contaminated in the lab in which it was stored and tested, Jonathan Ball, a professor of molecular virology at the University of Nottingham, tells the AP. “If he was infected (with COVID-19), then you would expect a more rapid and earlier spread of the virus in France than was seen,” he says in a statement.

Other experts say it’s possible the virus was spreading weeks before the first cases were confirmed in France on January 24, 2020.

“This gives a whole new picture on everything,” WHO spokesman Christian Lindmeier told a UN briefing in Geneva, according to Reuters. “The findings help to better understand the potential virus circulation of COVID-19,” he explained, and urged doctors in countries around the world to test unspecified cases of pneumonia for SARS-CoV-2.