This month, two independent cases of bird flu were detected in North American children without any known exposure to infected animals, raising concerns that the H5N1 virus that causes it is inching closer to evolving in a way that allows it to spread between humans.
Since April, 55 H5N1 cases have been reported in humans, and all but three have occurred in farmworkers in close contact with dairy cows or poultry, which the virus is infecting in droves. But health officials have not been able to determine the source of three cases in humans, raising questions about whether there is low-level community spread happening.
