Influenza A Virus Subtype H7N9 (H7N9)

H7N9 is a bird flu strain of the species Influenza virus A (avian influenza virus or bird flu virus). Avian influenza A H7 viruses normally circulate amongst avian populations with some variants known to occasionally infect humans. Cases continued to be reported throughout April and then dropped to only a few cases during the summer months. Influenza A viruses are divided into subtypes based on two proteins on the surface of the virus: hemagglutinin (HA) and neuraminidase (NA). The avian influenza A(H7N9) virus designation of H7N9 identifies it as having HA of the H7 subtype and NA of the N9 subtype. Avian influenza A H7 viruses are a group of influenza viruses that normally circulate among birds. H7 influenza infections in humans are uncommon, but have been confirmed worldwide in people who have direct contact with infected birds.