Washington: Public health officials are warning travelers and workers present at four U.S. airports on two recent days that they may have been exposed to measles from a traveler arriving from London.

Authorities said on Saturday that a New Mexico woman later confirmed to have measles arrived at Washington Dulles International Airport late in the afternoon of February. 20. Two days later, the measles-infected traveler departed from BWI Thurgood Marshall Airport near Baltimore on an evening flight to Denver, Colorado, and then on to Albuquerque, New Mexico.

The traveler became sick and was subsequently diagnosed with measles in New Mexico, said Tom Skinner, a spokesman for the Atlanta-based Centers for Disease Control and Prevention. He said on Saturday night that authorities in those states are trying to notify travelers who sat close to the infected passenger on the flights.

The New Mexico Department of Health's scientific laboratory division didn't identify the traveler by name but said she was a 27-year-old Santa Fe, N.M., woman who had not been immunized against measles.

"The appropriate steps are being taken to reach out to those passengers on the plane that were in close enough proximity," Skinner said of those seated five rows in front or behind the infected passenger.

Although most Americans have been vaccinated for measles or are immune because they've had the disease, public health officials are concerned about those not immunized, including babies. Pregnant women and those with weakened immune systems are also more at risk.

Authorities say people who were at the airports at the same time as the infected traveler and develop a fever or other symptoms should contact their doctors.

Dr. William Schaffner, an infectious disease specialist at the Vanderbilt University School of Medicine in Nashville, said the potential exposure of so many travelers in airport terminals is a cause for concern.

He said measles is 'highly communicable' and can be associated with complications leading to death.

"We don't want measles to be imported back into the U.S. once it gets a foothold," Schaffner told The Associated Press.

Although vaccinations have reduced measles cases in the U.S. to fewer than 150 annually since 1997, it remains a common disease worldwide with an estimated 10 million cases and 164,000 deaths globally each year, according to the CDC. That's why the center recommends that U.S. citizens traveling or living abroad remain up to date on immunisations.

The CDC says on its website that despite vaccinations in the U.S., health officials still see sporadic cases when visitors from other countries or Americans traveling abroad become infected and spread measles to those not vaccinated or unprotected against the virus.

A 2008 CDC report said the risk for measles transmission by air travel in the United States 'is considered low because of high US population immunity'.

Measles is a highly contagious respiratory disease caused by a virus, according to the CDC's web site. It typically produces fever, runny nose, cough, red and watery eyes and a body rash. The virus, which is spread by sneezing and coughing, can stay in the air for two hours.

Infection can lead to an ear infection or pneumonia in children, and in rare cases, death. Children in the U.S. generally are vaccinated starting at one year of age, and it is recommended earlier if they're being taken abroad.

People who are considered immune include those born in the United States before 1957, who previously had measles or who have had two measles vaccine shots.

Last week, Boston public health officials sought to contain a possible measles outbreak after an employee of the French consulate came down with the infectious disease earlier this month.