The U.S. Centers for Disease Control and Prevention on Thursday urged clinicians and laboratories to test for the bird flu within 24 hours in people hospitalized with influenza, as part of its efforts to tackle the ongoing infections in humans.

A child ill with fever and conjunctivitis in San Francisco tested positive for bird flu but had no known source of transmission.

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.