Twenty-one elementary students who became ill after smelling a strange odour on their school bus in Gatineau, Que., Friday morning have been discharged from hospital.

Students at École Saint-Jean-Bosco reported headaches and nausea, Gatineau police said.

Emergency crews were called to the school at 10:15 a.m. Friday.

Seventeen of the students were taken to the Gatineau Hospital and four to the Hull Hospital, Outaouais paramedics said.

Paramedics checked a total of 43 students for potential poisoning.

Carbon monoxide poisoning has been ruled out, according to the school board.

The bus is being inspected to determine what caused the smell and the symptoms.