4th human case of bird flu linked to dairy cow outbreak: CDC

The fourth human case of bird flu linked to the current dairy cow outbreak was confirmed on Wednesday in a dairy worker in Colorado, according to the Centers for Disease Control and Prevention.

Previously, one human case had been reported in Texas and two human cases reported in Michigan .

As with the previous cases, the patient is a dairy farm worker who came into contact with cows that tested positive for the H5N1 strain of bird flu, or avian influenza.

The worker was previously being monitored because of their exposure to infected cattle and reported symptoms to state health officials.

Testing results were inconclusive at the state level, but specimens forwarded to the CDC for additional testing were positive for influenza A, the federal health agency said.

The patient reported eye symptoms only. They received 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, long or unprotected exposures to sick or dead animals. People are also advised to avoid unprotected exposure to animal excrement, litter, unpasteurized milk or materials that have been touched by -- or close to -- animals with suspected or confirmed bird flu.

In early March, the U.S. Department of Agriculture announced a bird flu strain that had sickened millions of birds across the U.S. was identified in several mammals this year.

A few weeks later, federal and state public health officials said they were investigating an illness among primarily older dairy cows in Kansas, New Mexico and Texas and causing symptoms including decreased lactation and low appetite.

The USDA said in a statement at the time that "there is no concern 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 bird flu in livestock than any other state with 23 livestock herds affected in the last 30 days as of July 1, according to a USDA interactive dashboard .

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 the U.S. commercial milk supply remains safe because milk is pasteurized and dairy farmers are required to dispose of any milk from sick cows, so it does not enter the 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 shore up the national stockpile.