ST. PAUL — A hawk in western Minnesota is the first wild bird in the state to test positive for the bird flu virus since the beginning of an outbreak that’s killed more than 20 million birds in the Midwest this spring, state wildlife officials announced Thursday.

Officials have long said that wild birds could be spreading the flu, but warned that the positive test in the hawk doesn’t prove wild birds are the direct cause of the recent infections.

“This bird tells us our surveillance is working, but it unfortunately doesn’t provide many other clues about transmission of the virus,” Lou Cornicelli, wildlife research manager for the Department of Natural Resources, said in a statement.

Scientists and industry officials have said the virus also may be reaching captive birds via the feet of humans and rodents, or is being carried in by trucks, equipment, crates and egg flats.

Minnesota, the nation’s largest turkey-producing state, has been hit hard by the flu, with nearly 4 million birds killed by either the virus or euthanization. Nineteen counties have infected flocks. The state on Thursday announced presumed infections in three more flocks, two in Stearns County and one in Otter Tail. Only Iowa, with some 10 million birds — mostly egg-laying chickens — has lost more.

The H5N2 virus was detected earlier this year in at least three snow geese in Missouri and a goose in Kansas, but Minnesota officials had tested nearly 3,000 fecal samples from wild birds without finding the virus. They are also testing dead birds for the virus as well as hunter-harvested wild turkeys.

The Cooper’s hawk died in mid-April after flying into the deck of a home in Yellow Medicine County, and was tested after the homeowner reported it. That county isn’t among those that have had bird flu turn up in big poultry operations, but nearby Lyon County is.

A Cooper’s hawk in Washington state tested positive for the virus in January. Cornicelli said the hawks likely get it from something they eat.

The virus spreads quickly in confined flocks, but wild bird populations such as raptors and wild turkeys aren’t as vulnerable because they are dispersed.