Two coronavirus-infected people died in Santa Clara County in California on Feb. 6 and Feb. 17, making them the first documented COVID-19 fatalities​ in the United States. Until now, the first fatality was believed to have occurred in Kirkland, Washington on Feb. 29.

Across the country, there has been a growing concern that COVID-19 has been in the United States longer than experts first believed.

Earlier this month, physician and Santa Clara County Executive Dr. Jeff Smith said data collected by the Centers for Disease Control and Prevention (CDC), local health departments and others suggest it was “a lot longer than we first believed” — most likely since “back in December.”

Speaking with the Los Angeles Times, Smith said, “This wasn’t recognized because we were having a severe flu season. Symptoms are very much like the flu. If you got a mild case of COVID, you didn’t really notice. You didn’t even go to the doctor. The doctor maybe didn’t even do it because they presumed it was the flu.”

In Santa Clara County, which had previously reported its first COVID-19 death on March 9, the public health department said it will likely identify more deaths from COVID-19 as the Medical Examiner-Coroner continues to investigate area deaths.

Because COVID-19 symptoms can be slow to appear in infected individuals, and the time from onset of symptoms to death averages three weeks, the patient that died on Feb. 6 would have become infected in January at the latest.

With a recent study by the University of Southern California and the LA Department of Public Health showing that the Los Angeles County COVID-19 outbreak could be up to 55 times bigger than the number of confirmed cases, evidence is quickly mounting that the virus has been here in the U.S. far earlier than was originally suspected. As Dr. Smith noted, in all likelihood since December 2019.