Retrograde Motion

Four children in an Amish community in Minnesota have contracted the polio virus the first known infections in the U.S. in five years, state health officials said Thursday.

Dr. Harry Hull, the state epidemiologist, said the cases do not pose a threat to the general public because most people have been vaccinated against polio and are unlikely to have contact with Amish people. But he said he expects to find more infections within the Amish community because some of its members refuse immunizations on religious grounds.