July 16 (UPI) -- Up to 75% of the coronavirus strains circulating in New York City in early March shared genetic similarities with those seen in Europe and other areas of North America, according to an analysis published Thursday by the U.S. Centers for Disease Control and Prevention.
The findings are significant, given that they are based on samples of the new coronvirus, SARS-CoV-2, collected from patients at five hospitals in the city selected intentionally because "of their high use" by people who are "self-identified Chinese speakers," the agency researchers said.
COVID-19 is the disease caused by infection with the new coronavirus.
Samples tested in the study were gathered in early March at the start of the outbreak in New York, researchers said, and the hospitals were chosen "because of concern that SARS-CoV-2 could be introduced by travelers returning from China, where the outbreak originated."
"One of the major reasons why New York City was such an epicenter [for COVID-19] early on is [air travel]," William Hanage, associate professor of epidemiology at Harvard T.H. Chan School of Public Health, said during a conference call with reporters Wednesday.
"There were lots of flights going [to New York airports] from all over the world, including Europe," said Hanage, who was not part of the CDC analysis.
The U.S. government restricted travel from China on Feb. 2, more than a month after the COVID-19 outbreak was first identified in the city of Wuhan, the CDC researchers noted.
Travel from Europe was restricted on March 13, they said.
The 544 samples used in the new analysis were collected at New York City hospitals between March 1 and March 20, according to the researchers.
In all, 36 -- or 6.6% -- tested positive for COVID-19, including 14 -- or 12% -- among 119 children aged 18 years and under, they said.
Full genome sequences were generated from the 36 positive samples of the coronavirus, the researchers said.
In addition to the 27 samples "largely dominated by [genetic] sequences detected in Europe and other areas of North America, two samples featured genetic sequences similar to those found in cases in Washington state and seven shared similarities with samples collected in China or other parts of New York state," they said.
The findings of the CDC analysis are similar to those of a study published in June by the journal Science, which found that virus samples collected from 84 patients in New York City between March 9 and March 14 could be traced to cases in Europe and other parts of the United States.
A similar analysis, also published by Science in June, found at least seven different strains of the coronavirus circulating in California, which suggested that outbreaks there likely originated from several sources, including overseas travelers and from visitors from other U.S. states, the authors said.