WASHINGTON (REUTERS) - United Airlines believes the US Ebola patient flew on its aircraft from Brussels to Dallas-Fort Worth via Washington on Sept 20, based on information it received from federal officials, according to a company spokesman.

The US Centers for Disease Control and Prevention (CDC) said there was "zero risk of transmission" on these two flights because the patient showed no symptoms at the time and therefore could not have been contagious, the United spokesman said.

The CDC has said it is unnecessary to contact others who travelled on the flights, she added.

It is not yet known which carrier the patient took from Ebola-ravaged Liberia to Brussels.

"We are ensuring our employees have this information and suggest that any customers who have concerns contact the experts at the CDC for further information," the spokesman added.

The patient flew on flight UA 951 to Washington Dulles and flight UA 822 to Dallas-Fort Worth.

He was admitted to Texas Health Presbyterian Hospital on Sunday where he is in serious condition.