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.

The bird flu situation in the United States has evolved rapidly since April, when news about the virus infecting dairy cows made headlines. Here's what you need to know about the latest developments.

Missouri officials are under growing pressure from national public health experts to pinpoint the source of the state’s first human bird flu infection.