A contract medical screener at Los Angeles International Airport tested positive for coronavirus, the Department of Homeland Security said Wednesday.

The worker, whose last shift at the airport was on Feb. 21, is self-quarantined at home under medical supervision with mild symptoms, DHS said. The worker's immediate family is also quarantined, it said.

The county's board of supervisors and department of health declared a local and public health emergency in response to the growing number of cases in California, including six new cases in Los Angeles County.

The first Californian with coronavirus died Wednesday at a hospital in Roseville in northern California, officials said. The 71-year-old man is believed to have been exposed to the virus while on a cruise to Mexico last month.

There were 153 cases of coronavirus reported nationwide as of Wednesday, according to Johns Hopkins University. That includes 29 cases in California, according to the Centers for Disease Control and Prevention.

Eleven people have died in the United States, including 10 in Washington state and the cruise ship passenger in California.

LAX is one of 11 U.S. airports where inbound international travelers are screened for coronavirus. The DHS contract screeners ask travelers if they've been to affected countries, such as China, South Korea and Italy; if they have any symptoms of acute respiratory illness and check their temperature.

Heather Swift, a spokeswoman for DHS, said in a statement that the contract worker at LAX began experiencing cold-like symptoms on Feb. 29, and was administered a coronavirus test, which came back positive. DHS said it is working with its contractors to communicate with the screener's co-workers.

"We are told the individual wore all the correct protective equipment and took necessary protections on the job," she said. "At this time we do not know if this case is a result from community spread or through their work as a medical screener."

Swift said no passengers who had been screened at LAX had tested positive for coronavirus.

"This is an evolving situation," she said.