Both patients were dairy workers whose illnesses were mild. Investigators are continuing to evaluate the contacts of a Missouri patient who had no exposure to animals.

Hospital workers reported respiratory symptoms after encountering a Missouri patient with H5N1 who had not been exposed to farm animals. Officials say bird flu transmission is unlikely.

Chances are low that human-to-human spread of bird flu occurred in a group of people who were exposed to a patient infected with the virus in Missouri, US health authorities said.