Four new human cases of highly pathogenic avian influenza, or bird flu, infection in the state of Colorado have been confirmed by the U.S. Centers for Disease Control and Prevention (CDC), bringing the total cases to nine since 2022.

The four presumptive-positive cases were reported by the state on Friday, and the CDC confirmed the infection on Sunday, according to a press release.

All new cases were in farm workers who were involved in the depopulation of poultry at a commercial egg facility experiencing an outbreak of highly pathogenic avian influenza H5N1 virus.

These workers reported symptoms after being exposed to infected poultry. The CDC said they reported “mild illness,” including conjunctivitis and eye tearing, as well as fever, chills, coughing, sore throat and runny nose.

These are the first cases of bird flu infection in poultry workers since 2022 when the first-ever U.S. case of H5 in a poultry worker was reported in Colorado, said the CDC.

A CDC team is on the ground in Colorado, supporting the assessment of the poultry outbreak and associated human cases, said the CDC, adding that “these cases again underscore the risk of exposure to infected animals.”

Bird flu outbreaks have affected poultry in 48 U.S. states and 152 dairy herds in 12 states as of July 12, according to the CDC.