The pig didn't have symptoms, and further examination is under way to fully assess if infection occurred.
So far 15 of the human cases have been associated with exposure to H5N1-infected poultry, and 20 have been associated with exposure to sick or infected dairy cows.
In other developments, tests confirmed more human infections, outbreaks in California cows, and events in poultry in 3 western states.
As health officials brace for more cases in farm workers, Utah ag officials are moving quickly to monitor dairy cattle near a large outbreak at a layer farm.
In other developments, Quest Diagnostics will introduce an H5 molecular test by the end of the month, which should increase testing capacity.
The spurt of infections in Washington state is reminiscent of what Colorado experienced over the summer with illnesses in poultry cullers.
The probe detected the biomarker for H5N1 at three treatment plants, with two confirming that animal protein had already left processing facilities such as dairy farms.
Dairy workers in California continue to face a daunting threat from a virus surge in the state’s dairy cows, as federal officials confirmed 15 more outbreaks today.
The outbreak is Michigan's first since early September. Meanwhile, the USDA confirmed three earlier H5N1 detections in Florida dolphins.
In other avian flu developments, Utah reported an outbreak in commercial poultry in the northern part of the state.
