By Leah Douglas and Tom Polansek (Reuters) -People hospitalized for flu should be tested for bird flu within 24 hours, the U.S. Centers for Disease Control and Prevention said on Thursday, in an expansion of the agency's efforts to tackle ongoing infections in humans.

CDC officials say they extended the guidance now because they are seeing more H5N1 patients whose illness they cannot track back to an infected bird or cow.

The CDC is calling for expanded testing of bird flu after a child in California tested positive for the virus despite no known contact with animals.