MINNEAPOLIS (AP) — Animal health experts and poultry growers are scrambling to determine how a dangerous new strain of bird flu infected turkey flocks in three states — and to stop it from spreading.

Avian influenza is common in wild migratory waterfowl but doesn't usually harm them. But the H5N2 strain is deadly when it spreads to commercial poultry. It can wipe out a flock of tens of thousands of birds in a few days, as it did at a farm last month in Minnesota, the nation's top turkey-producing state. The same strain soon turned up on two farms in Missouri and one in Arkansas.

The vast majority of turkeys and chickens in the U.S. spend their lives confined indoors to protect against disease. Yet, as the infections show, viruses can still reach them — tracked in by humans or rodents; carried on trucks, equipment, crates and egg flats; passed from waterfowl to shore birds that find their way into a barn.

"This new guy is a bad actor," said Dr. Carol Cardona, an avian influenza specialist at the University of Minnesota.

Minnesota confirmed its outbreak March 4, the first H5N2 found in the Mississippi flyway, a major bird migration route. The Missouri and Arkansas cases were confirmed this week. The only known commonality is the flyway. Why it showed up at these locations simultaneously is a mystery, though Cardona and other experts suspect waterfowl or other wild birds.

Meanwhile, officials are keeping an eye on the workers who had contact with the infected flocks, and producers are tightening their standard biosecurity measures, which include putting on sanitary clothing and showering on their way in and out of barns.

The new strain — along with other recent outbreaks of highly pathogenic strains in commercial turkey and chicken farms, backyard flocks and wild birds in the Northwest's Pacific flyway — also affects the industry's bottom line in the affected states. Dozens of countries have banned poultry imports from affected states, a common practice done mainly to protect their own flocks.

The World Health Organization says avian influenza viruses can survive in contaminated raw poultry, so it's possible to spread them via fresh or frozen products. But government and industry officials say the danger to humans is very low, and people can't catch it from properly cooked poultry or eggs. Cardona said the likelihood of bird flu entering a country through imported products is "very, very low."

Some countries also use those bans to protect their markets from cheaper foreign products, according to Dr. Donna Carver, extension veterinarian at North Carolina State University. "There's not always a scientific reason," she said.

Minnesota, Missouri and Arkansas followed rapid response protocols from the federal government and poultry industry. Once H5N2 was confirmed at the farms, surviving turkeys were killed and kept out of the food supply. Officials quarantined the facilities and declared six-mile-radius restricted zones. They tested nearby farms but found no signs of other infected flocks.

"At least right now we're breathing a little easier," Missouri Department of Agriculture Director Richard Fordyce said.

To infect a commercial flock, the virus still needs to get into a barn. It spreads through bird-to-bird contact or via bird feces, so either a person, a bird or a rodent has to physically bring it inside. Modern biosecurity makes that difficult, so outbreaks in North America are rare.

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"I think the whole country is in lockdown mode in terms of trying to make sure that the biosecurity that they have is working the best it can," she said.

More than 7,000 patients at a Utah hospital were potentially exposed to an “outbreak” of hepatitis C after coming into contact with an infected former nurse – but less than half have come in for free testing to find out if they have the disease.

“We do consider this an outbreak,” Angela Dunn, a physician with the Utah Centers for Disease Control and Prevention, told the Standard Examiner. “When we have two or more hepatitis C-related infections, we consider it an outbreak.”

Only 35 percent of the 7,200 patients contacted to receive free testing have come forward so far, FOX13 reported.

“We’re hoping for about half at the end of the day, but we only have a few weeks left of free testing,” Dunn said.

Several people have already tested positive for the disease; however, the final tally of those infected isn’t expected to be released until February or March.

At least six U.S. residents have tested positive for the Zika virus, with officials in New York, Arkansas and Virginia confirming cases in each state.

Four people who had returned from travel abroad have tested positive in New York state with infections with the mosquito-transmitted Zika virus, local health officials said on Wednesday.