A sudden surge in cases of H7N9 bird flu in China is a "cause for concern," the Centers for Disease Control and Prevention said Friday.

It's infected 460 people just since October, the CDC said in a report. "It's by far the largest epidemic wave since 2013," said CDC flu expert Dr. Tim Uyeki.

Image: Health officials in protective suits put a goose into a sack as part of preventive measures against the H7N9 bird flu at a poultry market in Zhuji
 
Health officials in protective suits put a goose into a sack as part of preventive measures against the H7N9 bird flu at a poultry market in Zhuji, Zhejiang province on Jan. 5, 2014. Reuters file