Health officials believe people are contracting the virus through direct contact with infected fowl and say there has been no evidence so far that the virus is spreading easily between people.
Authorities have halted live poultry trade in cities where cases have been reported, and slaughtered fowl in markets where the virus has been detected.
The virus has been detected in live poultry in several food markets where human cases have been found, leading officials to think people are most likely contracting the virus through direct contact with infected fowl.
Wednesday, the Chinese Academy of Sciences said the H7N9 virus probably came from migratory birds from East Asia that mixed with domestic fowl in China's Yangtze River delta region around Shanghai.