Sixteen human bird flu cases have been reported in the United States this year, including the two workers who tested positive in California. Fifteen of those cases were in farm workers at infected poultry or dairy farms. Public health officials say the risk to the general public from bird flu is low.

Based on genetic information of the virus, officials say it appears migratory waterfowl initially introduced H5N1 bird flu to dairy cows in late winter of 2023 in a single, isolated event. But genomic experts say wild birds are not continuing to spread the disease in cattle.

Health officials in California are monitoring exposed workers for symptoms on two dairy farms where two human cases of bird flu tested positive, the U.S. Centers for Disease Control and Prevention said.