Health officials say none of the 54 residents have been diagnosed with coronavirus, but they are self-monitoring for symptoms.
Officials say the residents will spend the next two weeks in isolation. It is unclear where the residents live in the county.
"They are instructed to be in home quarantine, and we are monitoring them. They must take their temperature twice a day, checking for respiratory symptoms, and they must report that back to us," said Barbara Cole with Riverside County Public Health.
In San Diego County, they've been certified to do their own testing for coronavirus, which means results will come back sooner than if they'd have to wait for the CDC to do the testing.
Gov. Gavin Newsom says it's a step in the right direction.
"We haven't been testing as we should, and people should be prepared that when you do more testing the results will show more positive cases, but people shouldn't panic about that."
As the number of coronavirus cases in then U.S. grows, public health officials say they're monitoring anyone with travel histories in the most affected countries, including Italy, Iran, South Korea and Japan, but mostly China.
RELATED: Riverside County resident recently evacuated from cruise ship in Japan tests positive for coronavirus
A Riverside County resident who was a passenger on a cruise ship docked under quarantine in Japan tested positive for coronavirus, public health officials announced Tuesday.
The individual, who has not been publicly identified, is expected to fully recover from the virus, formally known as COVID-19, according to the Riverside University Health System.
About half of the United States' coronavirus cases are in California, where more than 8,400 people are being monitored in 49 different jurisdictions after arriving on flights from Asia, state health officials said.
Officials say there are 33 confirmed cases currently in California, but officials reiterate the risk to the public remains low.
RELATED: Coronavirus: Gov. Newsom says Calif. is prepared for first COVID-19 case with unknown origin
A new case of coronavirus was detected in Northern California in a woman who has not traveled overseas since the outbreak began. This suggests the virus could be spreading locally, person-to-person, the CDC said.
It is unknown how the woman contracted the virus. If it was contracted in the United States, it would be the country's first case of it spreading here, as opposed to being exposed overseas.
RELATED: Coronavirus: From hand-washing to wearing masks, here's how to protect yourself
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