A fourth farm worker has been infected with bird flu in the growing outbreak linked to dairy cows, health officials reported Wednesday.

The worker had direct contact with infected dairy cows on a northeast Colorado farm, state and federal health officials said. The man developed pink eye, or conjunctivitis, received antiviral treatment and has recovered.

Three previous cases of human infection linked to cows have been reported in dairy workers in Texas and Michigan since March. Two of those workers also developed pink eye, while one had mild respiratory symptoms, In 2022, the first U.S. case of bird flu was detected in a Colorado farm worker exposed to infected poultry.

The Centers for Disease Control and Prevention said the new infection “does not change” the agency's assessment that the risk to the general public remains low. Surveillance systems tracking flu in the U.S. have shown no unusual activity, officials said. However, people with prolonged contact with to infected birds or other animals, including livestock, or to their environments, are at higher risk of infection.

The Colorado man was being monitored when he developed symptoms because of his work with dairy cows, according to the CDC. Tests at the state level were inconclusive, but samples sent to CDC tested positive. Full results of genetic analysis of the sample are pending.

As of Wednesday, more than 135 dairy herds in a dozen states had reported infections with the H5N1 virus that originated in poultry, according to the Agriculture Department.