The virus has been confirmed at more than 270 dairies in central California, and traces were recently detected at a wastewater sampling site in Los Angeles County.

Cases have more than doubled in the United States within a few weeks, but researchers can’t determine why the spike is happening because surveillance for human infections has been patchy.

Concerns are growing about undiagnosed illness among farmworkers because of a lack of testing and safety precautions.

A new study lends weight to fears that more livestock workers have gotten the bird flu than has been reported.

Farmworkers face some of the most intense exposures to the bird flu virus, but advocates say many of them would lack resources to fall back on if they became ill.

Finland is offering farmworkers bird flu shots. Some experts say the U.S. should too.

The Centers for Disease Control and Prevention says a glitch in its bird flu test hasn’t harmed the agency’s outbreak response. But it has ignited scrutiny of its go-it-alone approach in testing for emerging pathogens.

Why did it take so long to recognize the virus on high-tech farms in the world’s richest country? Because even though H5N1 has circulated for nearly three decades, its arrival in dairy cattle was most unexpected.

Six people who work at a poultry farm in northeastern Colorado have tested positive for the bird flu.

The World Health Organization considers bird flu a public health concern because of its potential to cause a pandemic, yet the U.S. has tested few farmworkers.