So far, there have been 14 human cases of bird flu this year. All the patients — except the one from Missouri — had been linked to sick dairy cows or poultry.

The person is the 14th infected with H5N1 in the U.S. this year and the first to be hospitalized and to test positive without coming into known contact with an infected animal. The others, who were all described as having "mild" symptoms, had worked on farms known to have H5N1-infected cattle or poultry.

This is the 14th human case of bird flu reported this year in the United States and the first without a known occupational exposure to infected animals.