After someone in southwest Louisiana was hospitalized with a severe case of bird flu, the first such illness reported in the United States, health workers swabbed the person’s nose and throat, looking for genetic clues about the virus.

A genetic analysis of the bird flu in the body of a Louisiana man who contracted the first severe case found it mutated inside of his body, a development that could allow the virus to more easily spread to humans.

Samples from a hospitalized patient in Louisiana show changes that could make the H5N1 virus spread more easily between humans