Passengers and crew on two flights arriving in Philadelphia from Europe on Thursday were screened by medical teams after 12 people aboard became ill with flu-like symptoms, a day after a similar outbreak on a flight from Dubai to New York.
All 250 people on separate American Airlines flights from Munich and Paris were "held for a medical review" as a precaution, and the U.S. Centers for Disease Control and Prevention (CDC) was notified, airport spokeswoman Diane Gerace said.
Both of the flights had arrived at Philadelphia International Airport on Thursday afternoon, she said.
The CDC worked with Philadelphia health officers, emergency responders and Customs and Border Patrol agents to evaluate the passengers who reported feeling sick for influenza and other respiratory illnesses, CDC spokesman Benjamin Haynes said.
"Twelve passengers from the two flights reported sore throat and cough, none were identified with fever. None of the passengers are severely ill, and they will be released and informed of test results in 24 hours," Haynes said.
The rest of the passengers from the two flights were allowed to continue on to their destination, he said.
No one on either plane was quarantined, American Airlines spokeswoman Leslie Scott said. She said members of the crews had not contacted medical personnel ahead of landing to alert them of sick passengers on board.
On Wednesday, at least 19 people aboard an Emirates double-deck Airbus 380 plane were confirmed ill when the aircraft landed at John F. Kennedy International Airport. Ten of them were treated at a local hospital, reportedly also suffering from flu-like symptoms.
There was no indication the incidents, which occurred over two days at separate U.S. airports, were related.