The person, who has not been identified, last screened travelers for illness on Feb. 21, more than a week before exhibiting cold-like symptoms.
Officials said the medical screener was "highly trained and did everything right both on the job and when they began to feel sick," adding the worker "wore all the correct protective equipment and took necessary protections on the job."
"As soon as the individual began to feel sick, they self-quarantined, saw a physician, and reported to the appropriate authorities and officials," DHS spokesperson Heather Swift said.
The medical professional visited their primary care doctor on Sunday, one day after becoming symptomatic. The individual received a COVID-19 test at the doctor's office, which came back positive.
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The individual is under self-quarantine at home with mild symptoms and under medical supervision, officials say, and their immediate family is also under home quarantine.
It is unclear if this case is a result of community spread or through their work as a medical screener.
There have been no positive coronavirus detections reported from LAX-screened travelers, according to officials.
DHS said it is working to communicate with the individual's coworkers, and contract tracing is underway.
The news comes as the U.S. death toll from coronavirus climbed to 11, with a victim succumbing in Northern California - the nation's first reported fatality outside Washington state.
Officials in Placer County, northwest of Sacramento, said an elderly person who tested positive for COVID-19 Tuesday after returning from a San Francisco-Mexico cruise had died. The victim had underlying health conditions, authorities said.
RELATED: California officials announce 1st new coronavirus death in state
Also on Wednesday, Los Angeles County officials declared a state of emergency for the novel coronavirus as they confirmed six new cases of the potentially deadly infection in the county in the last 48 hours.
In addition, the county Department of Public Health announced a local health emergency in response to the increase in cases. There have been 7 reported cases across the county, with one individual recovering after falling ill in January.
The cities of Long Beach and Pasadena, which both have their own public health department separate from the county, also declared public health emergencies, though there are no confirmed cases in either city.
A South Korean flight attendant was diagnosed with coronavirus after flying into LAX. However, health officials said late last month that the attendant did not pose any risk to others while in Los Angeles County.
The impact of the Coronavirus is being felt all across Southern California. On Eyewitness News at 6 p.m. on Wednesday, we're dedicating our entire newscast to covering the impact and answering your questions. Watch it live tonight at 6 p.m. on ABC7 or on ABC7.com/live.
For in-depth coverage of the new coronavirus, go to www.abc7.com/coronavirus