(CBS) — Multiple passengers fell ill on separate international flights coming into Philadelphia International Airport on Thursday, CBS Philly reports. Officials said 12 passengers arriving at the airport on American Airlines flights from Paris and Munich experienced flu-like symptoms.

Multiple ambulances were dispatched to the airport.

All 250 passengers and crew on the flights were held for a medical review and the Centers for Disease Control and Prevention was notified to investigate. The CDC, Philadelphia Health Department and the Philadelphia Fire Department personnel performed medical evaluations on the passengers.

The passengers who did not fall ill are in the process of being released.

American Airlines told CBS News the planes were not quarantined, no medical was called to meet the plane and that it wasn’t until the passengers deplaned that some complained of feeling ill. They were being evaluated in the Customs and Border Protection area.

It is not yet known what caused the people to become sick. No one was transported.

This is a developing story and will be updated.