The entrance to LAX photographed in 2013. (AP Photo/Reed Saxon)

Los Angeles County health officials are alerting travelers about a possible measles exposure that happened at LAX late last month, the latest alarming development for a disease once thought to be eliminated in the U.S.

The infected passenger traveled through the airport's Terminal B, which handles international flights, and Delta Airlines' terminal, Terminal 3, between 9 a.m. and 9 p.m. on Feb. 21, according to L.A. County's Department of Public Health.

Terminal B has 29 gates and hosts a number of international airlines including Air France, China Airlines, Lufthansa, and Korean Air. Terminal 3 has 12 gates and home to Delta Airlines and smaller airlines like Interjet and Copa.

According to the flight numbers released by health officials, the person infected with measles, first landed at LAX's Terminal B in the morning of Feb. 21 on a China Eastern flight from Shanghai. He or she then went on to Terminal 3, Gate 32 to wait for a Delta flight to San Antonio, Texas.

L.A. County officials said they first learned about the case of the highly contagious virus on March 7.

BY THE NUMBERS

Last year, five cases were reported in L.A. County, according to the county's department of public health. This year, there has been one confirmed case in Pasadena where an international traveler came to the area and then returned back home.

California's last large measles outbreak — defined as three or more connected cases — was in late 2014 and linked to an infected person who went to Disneyland. That case was ultimately tied to 147 cases in seven states, as well as in Mexico and Canada.

This latest case has come to light at a time when measles outbreaks have reached 12 states, including California and Washington. According to the Centers for Disease Control and Prevention (CDC), more than 220 measles cases — which include six oubreaks — were reported between Jan. 1 and March 7, the first 10 weeks of this year. That's more than half the reported cases in all of 2018.

The resurgence of measles is very troubling for public health experts. In 2000, the U.S. declared that measles were eliminated. The CDC attributed the elimination to the MMR vaccination, which is up to 97 percent effective.

Measles is so highly contagious that if one infected person has it, then 90 percent of people close to the infected person and not vaccinated will be infected. The virus is best known for its rash, tiny white spots, it leaves behind. But the virus spreads through coughing and wheezing and can live up for up to two hours in the airspace where the infected person coughed or sneezed. Someone could be infected for days before the symptoms begin to appear. Measles can lead to brain damage, paralysis and even death.

So why is a disease thought to be conquered back? Health experts say it's due to parents who refuse vaccinations for their children. In 2015, post-Disneyland outbreak, California moved to toughen vaccine requirements. The law banned new exemptions based on personal or religious beliefs for students enrolled in daycare, preschool, and K-12 schools. High rates of vaccinations protect people who are unable to be vaccinated because of compromised immune systems, a concept known as herd immunity.

But the rebirth of measles isn't just happening in the U.S., which the LAX traveler underscores. Reports of measles cases worldwide jumped 30 percent in 2016 to 2017, according to the World Health Organization. So the CDC warns that outbreaks can be linked to people traveling internationally, especially to countries where there are larger outbreaks.

LACK OF STANDARD RULES

While California does have some of the toughest immunization regulations, Dr. Jeffrey Klausner, professor of infectious diseases at the David Geffen School of Medicine at UCLA, points out that vaccination requirements differ from state to state. And traveling is one of the quickest ways to spread measles.

"So what we need is federal leadership on this issue—with federal minimum standards across every state that require measles immunization and other communicable diseases immunization for school entry," says Klausner.

If you think you're developing measles symptoms, contact your doctor. If you haven't developed symptoms by March 14, you are no longer considered at risk of getting it from this exposure.

UPDATES:

4:47 p.m.: This article was updated with the date that people are considered no longered at risk from this exposure.

This article was originally published at 4 p.m.