- Amish and Mennonite shoppers in conservative dress mingled with shoppers from the wider public on a recent Friday at a vast outdoor market here, where vendors sold colorful pumpkins and mums, fry pies and squash, sports jerseys and Barbie accessories.

Such interactions are common in Lancaster County in central Pennsylvania, home to the largest Amish population in the U.S. - and the epicenter of the nation's worst measles outbreak in 35 years.

While they avoid many types of civic engagement for religious reasons, the Amish - like many other groups vulnerable to measles across the nation - are not truly separate.