I haven't heard whether the source was illegal aliens or not. There are not a lot of them here in town, although there are quite a few in other parts of the state. There is a rather large Bosnian immigrant/refugee population here in town; that's another possible source, if they were not immunized when they moved here. Or it could have just happened; I don't know.
"There are not a lot of them here in town"
Ever heard of airline flights where your fellow Iowa citizens have flown into your state after sitting on an airliner full of third worlders?