You're relying on a study from a Canadian in 2014. There have been many studies about this and while no one will ever be sure many studies point to outside Fort Riley.
"It’s not known whether it started in the pigs or chickens or birds flying overhead. But it spread to young farmers who, drafted for World War I, reported for duty at Fort Riley."
" No one knows for sure what farm, what family may have first fallen ill. The community was most likely Santa Fe, now a ghost town in Haskell County, says Darlene Groth, curator at Haskell County Historical Society in Sublette."