In the early 1990’s, hundreds of thousands of residents on the south side of Milwaukee experienced a massive outbreak of cryptosporidiosis, the intestinal disease caused by the cryptosporidium parasite. Most affected people experienced days of intestinal stomach flu-like symptoms (mainly diarrhea), but older and younger people along with those with compromised immune systems suffered far worse infections and effects. The source of the cryptosporidium was traced to a contaminated drinking water supply. Cryptosporidium can exist in any body of water, including hot tubs. Cryptosporidium contaminates water via human or animal feces. Once introduced to the water, unsuspecting hosts swallow and ingest the dormant parasite and become infected.Cryptosporidium is a robust and tough single celled parasite that can go into a dormant phase where it produces a thicker outside shell-like feature that allows it to survive in “hostile” environments. This explains why cryptosporidium is resistant to chlorine and other sanitizers in hot tubs.
How can hot tub owners prevent a cryptosporidium outbreak in their hot tubs? For starters, anyone who has contracted the parasite and become ill needs to stay out of hot tubs for several days after the symptoms have disappeared. Any small amount of contaminated fecal matter is enough to contaminate the hot tub.This type of prevention, however, is hard to enforce and verify and an awkward topic to talk about with guests. Furthermore, once an infestation has occurred, no amount of chlorine can be guaranteed to kill the parasite population, even if the tub is drained and cleaned!
There is another solution: treat your hot tub water with ozone. Ozone oxidizes live and dormant cryptosporidium parasites, leaving the water safe for use. In fact, ozone is so effective at killing cryptosporidium that the Milwaukee water utility installed ozone treatment as part of their corrective action after the outbreak in the 90’s.