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.

Health officials in California are investigating a possible third human case of bird flu, the California Department of Public Health announced Saturday.

Both patients were dairy workers whose illnesses were mild. Investigators are continuing to evaluate the contacts of a Missouri patient who had no exposure to animals.