Here is what I know : A relative of mine with business in China, flew back in mid January to Chicago to catch a connecting flight home to VT. He became ill a few days after. They were very aware of this health issues in China. Dr. contacted CDC. Test was flown up from CDC. A few days later CDC contacted Dr. the test did not work. Sending another. In the mean time a CDC rep contacted the patient daily for health check and other data requested. They were asked not to discuss it outside of the immediate contact group.
Looking at the flights from China to the U.S. daily during the early days and through January it is very easy to figure out the number of passengers that may have arrived unknowingly carrying covid-19. And so community spread began and quietly continued until March when the alarms were sounded.