Over a dozen cases of H5N1 have been reported among people in the United States this year. Current evidence suggests this bird flu virus spreads to humans only from infected animals, such as dairy cows and poultry, and not from person to person.
However, the latest case of human infection — reported Sept. 6 by the Centers for Disease Control and Prevention (CDC) — occurred in a person in Missouri who'd had no known exposure to relevant animals.
