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.

The Centers for Disease Control and Prevention issued an advisory Thursday urging health-care workers treating patients hospitalized with the flu to perform an additional test for bird flu within 24 hours of admission.

CDC officials say medical professionals are seeing more patients whose illness cannot be traced back to an infected animal or bird.