This electron microscope image provided by the Centers for Disease Control and Prevention shows the H7N9 virus which can take on a variety of shapes. Almost three weeks after China reported finding a ... more 
This electron microscope image provided by the Centers for Disease Control and Prevention shows the H7N9 virus which can take on a variety of shapes. Almost three weeks after China reported finding a new strain of bird flu in humans, experts are still stumped by how people are becoming infected when many appear to have had no recent contact with live fowl and the virus isn't supposed to pass from person to person. Understanding how the H7N9 bird flu virus is spreading is a goal of international and Chinese experts assembled by the World Health Organization as they begin a weeklong investigation Friday, April 18, 2013. (AP Photo/CDC, C.S. Goldsmith, T. Rowe) less 
1 / 11
Associated Press | Photo By CDC, C.S. Goldsmith, T. Rowe
Thu, Apr 18, 2013 8:41 PM EDT