The Centers for Disease Control and Prevention says hospitals treating people for the flu should test them for avian influenza within 24 hours.

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.

Public health officials have confirmed a San Francisco child is the second pediatric case of bird flu in the U.S. According to the CDC, no additional cases have been identified among the child's contacts.