H7N9 is a new 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. An H7N9 virus was first reported to have infected humans in 2013 in China. Most of the reported cases of human infection have resulted in severe respiratory illness. In the month following the report of the first case, more than 100 people had been infected, an unusually high rate for a new infection; a fifth of those patients had died, a fifth had recovered, and the rest remained critically ill. The World Health Organization (WHO) has identified H7N9 as "...an unusually dangerous virus for humans." As of August 31, 134 cases have been reported, resulting in the deaths of 45.
Human Infection with a Novel Avian-Origin Influenza A (H7N9) VirusNEJM
Sporadic human infections with avian influenza A virus, which usually occur after recent exposure to poultry, have caused a wide spectrum of illness, ranging from conjunctivitis and upper respiratory tract disease to pneumonia and multiorgan failure. Low pathogenic avian influenza A (H7N2, H7N3, H9N2, or H10N7)1-4 virus infections have caused lower respiratory tract illness that is mild (conjunctivitis or uncomplicated influenza-like illness) to moderate in severity. Most human infections with highly pathogenic avian influenza (HPAI) A (H7) viruses have resulted in conjunctivitis (H7N3) or uncomplicated influenza illness, but one case of fatal acute respiratory distress syndrome (ARDS) was reported in a patient with H7N7 virus infection during an outbreak in the Netherlands.1,5 In contrast, the cumulative case fatality rate since 2003 for reported cases of HPAI H5N1 virus infection is approximately 60%.