Two people sharing a home caught the virus without known exposure to animals. More than 30 human cases have been reported in the United States.

Human bird flu cases in California may be undercounted as farm workers avoid testing due in part to economic concerns, according to a labor union and a state expert.

The case concerned health officials and experts because human-to-human transmission of the H5N1 strain of avian influenza could mark the start of a new pandemic.