Today the Centers for Disease Control and Prevention (CDC) confirmed the fourth human case of highly pathogenic avian flu in the United States this year and the first in Colorado, as the state reported more infected dairy cows. Previous human cases were in Texas (one) and Michigan (two).

In a press release emailed to journalists, the CDC said the Colorado patient is a dairy worker who was being monitored because of work exposure to H5N1 virus-infected cattle.

“The person reported eye symptoms only, received oseltamivir [Tamiflu] treatment, and has recovered,” the CDC said. “Based on the information available at this time, this infection does not change CDC’s current H5N1 bird flu human health risk assessment for the U.S. general public, which the agency considers to be low.”

The first two agricultural workers infected in the United States, in Texas and Michigan this spring, also reported eye symptoms.

The US Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) has added two more H5N1 avian flu dairy herd outbreaks to its confirmed list, both in Colorado, raising its total to 139 affected herds from 12 states.

Colorado has had the most affected herds in the past 30 days, with 23 herds affected, APHIS said.