The case was confirmed in a dairy farmer in Colorado.
The fourth human case of bird flu linked to the current outbreak in dairy cows was confirmed Wednesday, according to the Centers for Disease Control and Prevention. It involved a dairy farmer in Colorado.
Previously, one human case was reported in Texas and two human cases in Michigan.
As in the previous cases, the patient is a dairy farmer who came into contact with cows that tested positive for the H5N1 strain of bird flu, also known as avian influenza.
The worker was previously monitored for exposure to infected livestock and reported his symptoms to state health authorities.
Test results were inconclusive at the state level, but samples sent to the CDC for additional testing came back positive for influenza A, the federal health agency said.
The patient reported only eye symptoms. They were given treatment with oseltamivir, an antiviral drug used to treat influenza, and have since recovered.
The CDC said the risk to the general public remains low, but advises people to avoid close, prolonged or unprotected exposure to sick or dead animals. People are also advised to avoid unprotected exposure to animal feces, litter, unpasteurized milk or materials that have been touched by — or near — animals with suspected or confirmed bird flu.
In early March, the U.S. Department of Agriculture announced that an avian influenza virus had been detected in several mammals this year, sickening millions of birds in the U.S.
A few weeks later, federal and state public health officials announced they were investigating a disease found primarily in older dairy cows in Kansas, New Mexico and Texas that caused symptoms including reduced lactation and decreased appetite.
The U.S. Department of Agriculture (USDA) said in a statement at the time that “there are no concerns about the safety of the commercial milk supply or that this circumstance poses a risk to consumer health.”
Currently, Colorado is reporting more cases of avian influenza in livestock than any other state, with 23 livestock herds affected in the past 30 days (ending July 1), according to an interactive dashboard from the U.S. Department of Agriculture.
In late April, reports emerged that bird flu fragments had been found in samples of pasteurized milk. However, the fragments are inactive remnants of the virus and cannot cause infection.
Federal agencies maintain that the U.S. commercial milk supply is safe because the milk is pasteurized and dairy farmers are required to dispose of the milk from sick cows so it does not enter the milk supply.
In May, the CDC said in a summary that it is preparing for the “possibility of increased risk to human health” from bird flu as part of the federal government’s preparedness efforts, including filling doses of bird flu vaccine into vials to replenish the national stockpile.