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.

“This is an astonishing number in a short period of time, illustrating how globalized our world has become. Just as people can hop continents with amazing ease, the infections they carry can too,” said Dr. Vinayak Kumar, an internal medicine resident at the Mayo Clinic and a contributor to the ABC News Medical Unit.

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 shows that globalization is here, and we have to be better prepared to deal with the impact this will have on all our lives in so many ways.”