Health officials in California are monitoring other exposed workers for symptoms on two dairy farms where two human cases of bird flu were confirmed on Thursday, Reuters reported, citing the US Centers for Disease Control and Prevention.

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 frombird flu is low.

The sick workers had only conjunctivitis, or pink eye, and did not report respiratory symptoms, Nirav Shah, principal deputy director at CDC, said on a Friday press call.

More than 250 dairy herds in 14 states have tested positive for bird flu this year, including 56 in California, according to the US Department of Agriculture.

The CDC is continuing to investigate whether any healthcare workers may have been infected with bird flu after one person tested positive in Missouri, Shah said.

The agency’s testing of seven blood samples from healthcare workers who were exposed to the sick person, which would indicate whether they had previously contracted the virus, could take another two weeks, he said.

The bird flu strain detected on the two California farms is the same as has been detected on dairy farms in other states and the affected farms are quarantined, Eric Deeble, deputy under secretary for marketing and regulatory programs at USDA, said on the call.

Colorado, which in the spring was a hot spot for bird flu spread on dairy farms, now has just one positive herd, indicating success of the state’s mandatory bulk milk testing, Deeble said.

Pasteurized dairy products remain safe to consume, Steve Grube, chief medical officer at the Food and Drug Administration’s Center for Food Safety and Applied Nutrition, said on the call.

The FDA said on Thursday that it will soon launch a study of raw cow’s milk at some dairy plants to better understand the prevalence of thebird flu virus in the milk supply.