The first confirmed coronavirus case was announced in Louisiana on March 9, but it’s likely the disease was circulating silently through New Orleans in the weeks before that. Now, researchers are taking the first steps toward understanding the path the disease took to arrive at the city's front door.

A team of scientists from Ochsner Health System and BioInfoExperts, a biological analysis service based in Thibodaux, La., are sequencing the genome of the virus from patient samples to learn how it got here, where it has spread since its arrival and possibly why it affects some people more than others.

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Genome sequencing has been used in the past to determine how diseases like HIV jumped from different species to humans in Africa. And in New Orleans, it may be able to determine whether or not Mardi Gras brought this disease into the city like many public officials have speculated.

“People came here from all over the world and then went back home,” said Susanna Lamers, CEO of BioInfoExperts. “And we’ll be able to identify those exact transmission paths.”

Viruses replicate by taking over living cells and injecting them with a snippet of genetic material called RNA. When the virus makes copies of the RNA, mistakes sometimes get made — like the jumbled phrases that happen during a game of telephone. Those mistakes act as a road map for scientists who are trying to track the path of a particular strain of virus.

“We tend to think about who infected who,” said Lamers. “But as these viruses are transmitted they accumulate mutations.”

Those mutations give scientists a timeline and a map and may also help them figure out if some strains batter the body more than others.

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Right now, the team has sequenced just two of the 100 New Orleans-area samples they intend to sequence. An additional sequence was completed by the Centers for Disease Control and Prevention with material from Baton Rouge.

All three sequences have indicators that tie them to the U.S. Northwest. Although the researchers say the data are too limited to draw any conclusions on how the virus made it to New Orleans, they were somewhat surprised by the common origin.

“Given Mardi Gras, we expected to see a lot of variation,” said Amy Feehan, a research scientist at Ochsner. “Those were very closely related. Maybe that’s the luck of the draw, but moving forward I would expect to see some that are not so closely related.”

A similar study in New York City found that most of the viruses in that region originated from Europe, not China, and began spreading in mid-February, a few weeks before the first case was announced there.

Hundreds of genomes will need to be sequenced before stronger conclusions about the disease in New Orleans can be drawn, said Bob Garry, a Tulane University virologist who has tracked diseases like Ebola and HIV and is also working to sequence genomes for coronavirus.

If the strains continue to match those from the Northwest, it would indicate it was spread by one person infecting many others. That was the case in South Korea, where that country's CDC found that a church group was related to almost 50% of the country’s infections.

“We saw that was the kind of event that got explosive,” said Garry. “If the sequences are very diverse, that was Mardi Gras,” he said.

More genome sequencing will point us in the right direction, he said.

“I don’t think we should pick on Mardi Gras to explain why this virus hit New Orleans any harder than anywhere else,” said Garry, who pointed out that the city’s high number of people living with other diseases could explain why it took off. “But we’ll see. I’m willing to let the data take us in any direction.”