Background and summary of human infection with avian influenza A(H7N9) virus, WHO, 31 January 2014

The influenza A(H7N9) virus is one subgroup among the larger group of H7 viruses, which normally circulate among birds. 

Human infections with other subgroups of H7 influenza viruses (H7N2, H7N3, and H7N7) have previously been reported in Australia, Canada, Italy, Mexico, the Netherlands, the United Kingdom and the United States of America. Most of these infections occurred in association with poultry outbreaks. The infections mainly 

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