Flu: Cases spiking across the U.S.

CDC: Flu activity rising nationwide as winter sets in

Health officials in Illinois are warning of a new and unexpected mutation that could make for a "more serious flu season" as cases are already on the rise. The new variant, known as "Subclade K," is part of the H3N2 parent group, or a type of Flu A. "This mutation has been associated with an increased rate of flu infections in countries that are already witnessing it and also in parts of the United States," said Illinois Department of Public Health Chief Medical Officer Dr. Arti Barnes. #fluseas

A mutated strain of influenza A, H3N2 subclade K, is surging worldwide, sparking concerns about a severe flu season in the U.S. Here's what to symptoms to look out for. | NBC 7 San Diego