The bird flu virus found in a severely ill patient hospitalized in the United States has mutated to become better adapted to human airways, though there is no evidence it has spread beyond the individual,

The ongoing spread of bird flu in the United States has alarmed experts -- not just because of human cases causing severe illness, but also due to troubling new instances of infections in cats. A sample of the virus found in a critically ill patient in the United States has shown signs of mutating to better suit human airways,

Here’s what to know about the United States’ first confirmed severe case of H5N1 avian influenza—and how to protect yourself.