Data: Virus likely ignited in U.S. about mid-January

Those who thought they had virus earlier likely had the flu.

The spark that started the U.S. coronavirus epidemic arrived during a three-week window from mid-January to early February, before the nation halted travel from China, according to the most comprehensive federal study to date of when the virus began spreading.

That means anyone in the U.S. who thought they had the virus in December or early January probably had the flu, public health researchers said.

Some people have claimed Americans were getting sick from the coronavirus as early as November and that infections were spreading in the U.S. before any case was identified, said Dr. Robert Redfield, the head of the U.S. Centers for Disease Control and Prevention.

“(This) puts data into the discussion. Prior to this we had discussion without a lot of data,” he said.

In the study released Friday, CDC researchers collaborated with health officials in six states as well as genetics researchers and disease modelers in the Seattle area.

They drew on four kinds of data. One was reported illnesses by hospital emergency departments across the country. Another was a look back at about 11,000 respiratory specimens collected in January and February. A third was a genetic analysis of viruses taken from patients in California, Washington

and the Northeast. Finally, autopsy findings from California also fit the theory.

The new coronavirus emerged in Wuhan, China, late last year. The first U.S. infection to be identified was a traveler: a Washington state man who returned from Wuhan on Jan. 15 and sought help at a clinic on Jan. 19.

The White House announced a ban on travelers from China on Jan. 31, with implementation beginning on Feb. 3.

Before that, some travelers were screened for symptoms at some airports. Only later did health officials realize the virus could spread before symptoms show up, rendering symptom-based screening imperfect.

The study found a limited spread in some communities was occurring in late January and early February.

Early instances of infection were found in the 11,000 airway samples collected from six states. The earliest was in a sample collected Feb. 21 in the Seattle area.

Genetic analysis from early cases suggests a single lineage of virus from China began spreading in the United States between Jan. 18 and Feb. 9.

MISHA FRIEDMAN / NEW YORK TIMES Blood samples at a Brooklyn, New York, lab Tuesday are used to study coronavirus. Analysis suggests a single lineage of virus from China began spreading in the U.S. between Jan. 18 and Feb. 9.