Data collected by the Centers for Disease Control and Prevention suggest the coronavirus has been present in the United States as early as December.

Coronavirus deaths in the San Francisco Bay Area in February and March are leading scientists to believe that the virus was present in California earlier than previously believed, according to the Los Angeles Times.

“The virus was freewheeling in our community and probably has been here for quite some time,” Dr. Jeff Smith, chief executive of Santa Clara County's government, told county leaders in a briefing.

“This wasn’t recognized because we were having a severe flu season,” Smith said. “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.”

Smith said Friday that data collected by the Centers for Disease Control and local health departments suggest that the virus was in California “a lot longer than we first believed,” likely since “back in December.”

There was very little community testing in California in January and February, which contributed to the uncertainty as to when exactly the virus first appeared.

“When public health [officials] tried to track down the start of the disease … we weren’t able to find, specifically, a contact,” Smith added. “That means the virus is in the community already — not, as was suspected by the CDC, as only in China and being spread from contact with China.”

In the state of California, 596 people have died, and more than 21,000 people have been infected.