Researchers have found that most coronavirus cases in New York City originated from Europe, not Asia.

The research - which relies on testing the coronavirus genomes - reports that early cases began circulating in New York City around mid-February, much earlier than the announcement of the first reported cases in early March.

Speaking to The New York Times, Harm van Bakel, a geneticist at Icahn School of Medicine at Mount Sinai, confirmed that the American infection was primarily carried over from Europe, not Asia.

"Taken together, these results show that SARS-CoV-2 came to New York City and environs predominantly via untracked transmission between the United States and Europe, with only limited introduction from China, where the virus originated, or other locations in Asia," a press release announcing the discovery said.

Another team at NYU's Grossman School of Medicine reached a similar conclusion despite studying a different group of cases.

Until now, there was no evidence that the virus had been spreading significantly before early March. Now, it appears that early, aggressive testing could have prevented the widespread infections that currently plague the country.

Dr Adriana Heguy, a member of the research team at NYU, said "people were just oblivious."

"It was a disaster that we didn't do testing," she said.

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The first steps President Donald Trump took to fight the virus in the US was to enact travel bans, but those did not begin until March 11. By then, the virus had already been spreading for weeks.

Initial testing done in the US was aimed specifically at individuals coming from China and who had displayed COVID-19 symptoms.

The earliest cases - those in Washington - were traced back to the original outbreak in Wuhan, China, but subsequent tests of the earliest New York cases revealed viruses with different mutations than the Washington cases, suggesting the viruses were imported from elsewhere.

"That's when you know you've had a silent transmission for a while," she said.

The researchers at Mount Sinai realised the cases they were seeing in New York were practically identical to the ones found circulating Europe. Though they don't know which specific flight brought the virus from Europe to New York, they believe it took place between late January to early February.