I don't know if this is the same group or not(it seems likely that it is) - but there was a previous article about a family of Amish that the kids all had exposure. It was actually vaccine related. From an Oral Vaccine (which is no longer used in the states) that contained the live virus - presumably from Canada.
Interesting. I would like to read that. I always try to remember to stay away from folks whose immune systems are compromised whenever our children have vaccines, particularly the oral polio vaccine.