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

The CDC has confirmed a total of 66 human cases of bird flu across the United States as of Friday, although the number is believed to be higher.

A genetic analysis suggests the bird flu virus mutated inside a Louisiana patient who contracted the nation’s first severe case of the illness, the U.S. Centers for Disease Control and Prevention said this week.