A Michigan dairy farmworker has recovered from mild eye symptoms after testing positive for bird flu, marking the second case documented in humans in the United States.

Farmers two states to the west in Minnesota remain on guard about the possibility of highly pathogenic bird flu infecting dairy herds or farmworkers. There's also concern in the state's nation-leading turkey industry.

"Still no positive results in Minnesota's dairy herds," said Michael Crusan, spokesman for the Minnesota Board of Animal Health. However, a slew of positive cases in poultry and commercial egg-laying flocks were detected over the weekend, stirring concern.

On Tuesday alone, 1.3 million birds in Meeker County, 51,000 in Morrison County and 22,000 and 7,500 in Stearns County turned up positive tests confirmed by the board.

There are 160 infected sites in Minnesota, and nearly 8 million birds statewide have become infected since the start of the H5N1 outbreak in 2022.

Before the most recent infections, there'd only been five flocks infected in all of 2024, according to the Animal Health Board.

Lucas Sjostrom, executive director of the Minnesota Milk Producers Association, said the state's dairy farmers continue to "closely watch and learn" about transmission of bird flu to dairy herds.

"At the farm level, as you can imagine, dairy farmers always make the health and safety of their cows a top priority, including biosecurity protocols," Sjostrom said in an email.

Bird flu has presented mild cases of eye irritation in the two infected U.S. workers. Fifty-two herds in nine states have tested positive for the disease, according to the U.S. Department of Agriculture.

Unlike birds, cattle can recover from the illness. Health officials say pasteurized milk sold in grocery stores remains safe to drink.