This is why the UK says, handwashing with soap and water only at any petting farm or zoo.

A recent cluster of cryptosporidium cases cropped up after a Iowa preschool class visited a farm, Dr. Patricia Quinlisk, the Iowa Department of Public Health’s medical director, reported this morning. “While on the farm, the children petted cows and ate snacks,” Quinlisk wrote in a weekly email to public-health officials statewide. “The children did use hand sanitizer before eating; however, hand sanitizers are not particularly effective against crypto. Please continue to encourage handwashing with soap and water whenever possible.”

The Des Moines Register reports the parasite sickened hundreds of Iowans this summer, mainly via tainted swimming-pool water. Many of the patients suffered severe diarrhea. The outbreak has slowed now that most public pools have closed for the season. But infections also can happen in other ways, including contact with infected animals.

Quinlisk did not identify the preschool or say how many children became ill.

On Sept. 12, the state health department reported that there had been 861 confirmed or probable cases in Iowa so far in 2013. In all of 2012, there were 328 such cases.