3.4 million travelers poured into US as coronavirus pandemic erupted

An ABC News investigation offers sobering insight into how COVID-19 has spread and penetrated so broadly, so deeply and so quickly in the United States. It also helps explain why Americans, no matter where they live, must continue to heed the warnings of health officials to self distance and why the virus likely was here far earlier than first realized.

With the advent of COVID-19, the world has officially entered a dangerous new phase where a surge in international travel in recent decades served as the springboard -- jet fuel, really -- for an infectious disease potentially to kill hundreds of thousands in the U.S. and infect the global economy at breathtaking speed.

Travel data of passengers arriving in the United States from China during the critical period in December, January and February, when the disease took hold in that country, shows a stunning 759,493 people entered the U.S.

Those travelers from China included more than 228,000 Americans returning home and hundreds of thousands of Chinese nationals arriving for business, academics, tourism or to visit family.

"The numbers are clearly alarming," Dr. Simone Wildes, an infectious disease specialist at South Shore Health, told ABC News.

"It is difficult to estimate the portion of travelers coming from China to the U.S. with COVID-19, but fair to speculate that a large number might have been infected at the time of travel."

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