Stock Photo - This colorized negatively-stained transmission electron micrograph (TEM) captured some of the ultrastructural details exhibited by the new influenza A (H7N9) virus. On April 1, 2013, the World Health Organization (WHO) first reported 3 human infections with a new influenza A (H7N9) virus in China. Since then, additional cases have been reported. Most reported cases have severe respiratory illness and, in some cases, have died. At this time, no cases of H7N9 outside of China have been reported. This new H7N9 virus is an avian (bird) influenza (flu) virus. Human infections with avian influenza (AI, or ?bird flu?) are rare but have occurred in the past, most commonly after exposure to infected poultry. However, this is the first time that this bird flu subtype (H7N9) has been found in people. This virus is very different from other H7N9 viruses previously found in birds.