The new test results made public late Tuesday show that even this timeline failed to reveal how long the virus had been circulating. Ms. Dowd had not recently traveled outside the country, the authorities said, and yet she died a full 20 days before the earliest recorded case of community transmission. Another previously unconnected death in Santa Clara County, on Feb. 17, has also now been linked to the coronavirus.

“Each one of those deaths is probably the tip of an iceberg of unknown size,” Dr. Sara Cody, Santa Clara County’s medical officer, said in an interview…

“She traveled all over for her job. Germany. Austria,” said her brother-in-law, Jeff Macias, who said she had also traveled at times to China.

She had gone to Beijing in November, according to the longtime friend.