The highly contagious parasite is difficult to get rid of because chlorine doesn't always kill it, according to the Mayo Clinic. It's passed through stool and is typically transmitted through contaminated drinking water or recreational water facilities that have infected fecal matter in them. The parasite was first discovered in Maricopa County, which encompasses Phoenix, on Aug. 4 after 19 cases were reported in July. Last July, there had only been four cases, according to NBC affiliate.
source: NBC News