Water pollution in Galway, Ireland illustrates health problem of concern to all cities

The BBC is reporting that Irish city Galway has been struck by a cryptosporidium outbreak that is causing a crisis for the city. Cryptosporidium is a protozoan that can cause severe vomiting, diarrhea, and stomach cramps in humans (cryptosporodiosis). What's worse, infestation  by this intestinal parasite can be fatal to children, the elderly, and those with compromised immune systems, such as AIDS patients.

Galway is not the first city to be struck by such a crisis, nor is it likely to be the last. Cryptosporidium spreads by use of an oocyst phase that is not affected by chlorine or most other common disinfectants. Once this water-borne parasite invades a water supply, it is likely to cause illness in up to 50% of the citizens drinking the affected water.

A major outbreak of cryptosporidium occurred in Milwaukee, Wisconsin in 1993 and killed more than 100 people out of an estimated 880,000 served by the affected water treatment facility. The plant was shut down, but during the two week period that was still open, 403,000 residents became ill. This was the worst waterborne disease outbreak documented in United States history.

Ozonation and treatment with ultraviolet light have been shown to be effective treatments for disabling the protozoan, but filtration and boiling are the most commonly used methods to achieve water safety.

Unlike many parasites, cryptosporidium passes its entire life cycle in a single host, so an infected host will excrete oocysts in feces.