The patient got measles after traveling internationally.
This case is not related to any of the measles cases announced earlier this year.
Nationally, there have been more than 700 cases in 22 states reported this year, the highest number in 25 years.
The patient traveled abroad through Tom Bradley International Terminal at Los Angeles International Airport on April 23 between 4 p.m. and 7:30 p.m., rode on a Fox Auto Parks shuttle on that day, and visited the Home Depot on 20th Street in Lancaster three days later, between 8 a.m. and 11 a.m.
Anybody who visited any of those locations during those time periods should call their health provider and confirm their immunization records.
The health department says there have also been five non-residents with measles who traveled through L.A. county.
Some 200 students and employees were in quarantine after potential exposure at UCLA and Cal State L.A. The quarantine at UCLA ends Tuesday, but will continue for a few more days at Cal State L.A.
Meanwhile, L.A. County supervisors are entering a motion to promote awareness aimed at containing the spread of the virus.
"We're going to support a bill in Sacramento that will help us identify those who have decided not to be vaccinated, and see what we can do to make sure that they have legitimate excuses on why they haven't been vaccinated. Measles is highly contagious. We need people to be vaccinated, so we're going to up our game," said L.A. County Supervisor Janice Hahn.
County supervisors say some people are opting out of getting immunized using a loophole in the law that provides them or their children a waiver from a doctor.