Five people were taken to hospital after the aircraft landed at Philadelphia International Airport, according to fire department officials.
Local reports said some passengers had vomited and a further seven had felt sick as a result of the smell.
Airport spokeswoman Victoria Lupica said the US Airways airbus had taken off from Charlotte, in the state of North Carolina, and was bound for Rome before it was diverted on Tuesday evening.
The pilot's decision to land the aircraft prematurely was "out of an abundance of caution", US Airways spokesman Todd Lehmacher said.
He added that five crew members were seen by a paramedic before being taken to a hospital for observation.
The plane is expected to continue to Rome with a new crew this morning.