The latest patient is fully vaccinated and received a booster, according to the L.A. County Public Health Department.
"The individual had mild symptoms and had multiple close contacts who have since tested positive and are self-isolating," the department said in a news release. "Several of the close contacts are fully vaccinated, while the vaccination status of some is still being determined."
The health department said it's working to determine if those additional cases are of the omicron variant.
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"The identification of a case of Omicron attributed to community spread is a reminder that we all need to take necessary precautions to prevent transmission of COVID-19," county Public Health Director Barbara Ferrer said.
The county did not provide other details of the new omicron patient, only calling the case "a possible result of local transmission," meaning the variant is now being spread within the community.
Los Angeles County reported its first omicron case last week, involving a person who had traveled to South Africa via London. The second and third cases were confirmed Monday -- one involving a USC student who had traveled to the East Coast for the Thanksgiving holiday, and another involving a person who had recently traveled to West Africa.
All three infections were deemed by health officials to be "travel-related," and all three patients were fully vaccinated and experienced only mild symptoms, county officials said.
The city of Long Beach, which has a health department separate from the county, confirmed its first omicron case Tuesday. That person was also fully vaccinated, did not develop any symptoms and had recently traveled internationally, but not to the southern Africa region.
City News Service contributed to this report.
The video in the media player above is from a previous report.