CRYPTOSPORIDIUM

Cryptosporidium is a protozoan and an intracellular parasite that infects a variety of animals including humans. It is a round oocyst 4 to 6 microns in diameter that was first recognized as a cause of human illness in 1976. Infection can occur from drinking contaminated water, eating contaminated food, exposure to fecally contaminated surfaces and from person to person exposure via the fecal-oral route when hands are not properly washed. Person to person infection is well documented in places like day-care centers and hospitals. There are also many routes for waterborne transmission.

All surface water may harbor Cryptosporidium contamination. Oocysts have been found in lakes, rivers, streams, reservoirs and treated surface water. The organism is widespread, although concentrations vary. For example, a study of 181 surface water sources showed 93 contained Cryptosporidium. Contamination of ground water is also possible; in one survey, as many as 20 percent of test wells contained the oocyst.

Symptoms of cryptosporidiosis include diarrhea, abdominal cramps, nausea, vomiting and low-grade fever. The illness typically lasts 10 to 14 days, but can last up to 30. There is no cure and recovery depends on the patient's immune system. Certain treatments reduce the severity of some of the symptoms, but the disease can be fatal for people with certain health conditions. In severe cases it develops into a prolonged, life-threatening, cholera-like illness. People with weak immune systems are most vulnerable.

Cryptosporidium oocysts resist chlorinating and the use of chlorine dioxide. Oocyst viability wasn't affected by exposure to even 30,000 parts per million (ppm) chlorine as sodium hypochlorite for up to 18 hours. It takes sodium hypochlorite at higher than 700,000 ppm concentrations to eliminate the oocyst. These doses cannot be used in practical applications.

Effective treatment methods include ozone, ultra-violet and physical filtering by a fine enough, uniform and bypass-resistant filtering device. There is some evidence that the oocyst can range down in size to 2.5 microns. This and the flexibility of the oocyst when it is subjected to filtering forces, indicate the need to select a quality filter.