The infected patient had traveled on the Grand Princess cruise ship from San Francisco to Mexico and returned to the port of entry in that city on Feb. 21, 2020, Ventura County spokeswoman Ashley Bautista said in a statement.
An elderly person traveled on the same ship and later died in Northern California's Placer County after testing positive for COVID-19, the news release said.
More than 22 million Californians now eligible for free medically necessary COVID-19 screenings
"The cruise destination was not on the list of at-risk destinations so the travelers that disembarked the ship on February 21, 2020 were not under travel restrictions or health checks upon return," the statement said.
The Ventura County Public Health Lab, one of eleven labs in the state able to conduct testing, confirmed that county's novel coronavirus case on Thursday, Bautista said. Secondary confirmation is pending from the Centers for Disease Control and Prevention.
The patient did not feel well after returning from the cruise and remained at home to rest, officials said. The patient left home only to seek medical attention.
"The patient is currently under home quarantine with mild symptoms," the statement said. "The patient's spouse was also on the cruise but has no symptoms," and also remains under home quarantine.