Two farmworkers in California tested positive for H5 bird flu, the US Centers for Disease Control and Prevention confirmed on Thursday.

Although California dairy farmers anticipated a bird flu mortality rate of less than 2%, some say between 10% and 15% of infected cattle are dying.

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.