Key facts. 1  Avian influenza (AI), commonly called bird flu, is an infectious viral disease of birds. 2  Most avian influenza viruses do not infect humans; however some, such as A(H5N1) and A(H7N9), have caused serious infections in people.he incubation period for A(H5N1) avian influenza may be longer than that for normal seasonal influenza, which is around 2 to 3 days. Current data for A(H5N1) infection indicate an incubation period ranging from 2 to 8 days and possibly as long as 17 days.