The latest developments are highly concerning, as they raise the possibility that the H5N1 virus has evolved the ability to transmit from human-to-human and thus the potential to cause the next pandemic.

At least one household member and six healthcare workers who encountered the index case-patient are being investigated after showing symptoms of viral infection.

At least eight people may be infected with H5N1 bird flu in Missouri, marking the first cluster of the disease spreading between humans in the United States. The first case of a human contracting bird flu with no known animal contact happened in Missouri in August,

Four more health care workers are being treated for respiratory symptoms after being exposed to bird flu - bringing the total number of possible cases to seven. Emory's Dr. Neil Winawer discusses the significance of the recent findings with Alyse Eady.