Airport spokesman Phil Orlandella said United Flight 903, which originated in Munich, was diverted to Boston at about 2:30 p.m. Friday after a 53-year-old female passenger told flight attendants about her symptoms.
The plane's captain made the decision to stop as a precaution, Orlandella said.
"Out of an abundance of caution, we contacted the CDC, who advised us to divert the flight to Boston, where the plane was met by paramedics, who tended to the customer," United Airlines rep Megan McCarthy said in a statement. "The crew followed all procedures, as we would with any customer reporting these symptoms."
Television footage showed a woman being led from the plane by emergency workers to a waiting ambulance. It isn't yet clear what caused the woman's symptoms or whether she might be suffering from swine flu.
The flight, which had 245 passengers and 16 crew members, continued to Dulles.