Sanitary Engineering Division

Cryptosporidium

Cryptosporidium is a waterborne parasite that resides in the intestinal tract of mammals and other animals. It becomes waterborne when fecal material is washed into rivers, lakes, and other bodies of water. It can be transmitted by ingesting contaminated water or food, or by person-to-person contact. It can also be transmitted in swimming pools if there are any infected persons using the pool who have "fecal accidents". The infective dose can be very low; as few as 10 organisms have been demonstrated to cause illness in animals. The illness caused by Cryptosporidium has an incubation period of 2 to 10 days with an average of about 7 days. The most common sign or symptom of illness is diarrhea which is usually profuse and watery and often accompanied by abdominal cramping. Malaise, fever, loss of appetite, nausea, and vomiting can also occur.

Oocysts, the infectious stage of the organism, appear in the stool at the onset of symptoms and can continue to be excreted in the stool for several weeks after the symptoms resolve. Outside the body they may be infective for 2 - 6 months in a moist environment.

The oocyst state is highly resistant to halogen (chlorine/bromine) disinfection. It can withstand relatively high levels of hypochlorous acid for a long period of time. This is a concern in pools where the primary protection against disease transmission is the halogen disinfection system.

Because of the size of the oocyst (2 - 4 microns in size), they can pass through a sand filter or most cartridge filters. A diatomaceous earth filter can capture most of the oocysts. However, even with good removal it may take as long as 21/2 days to remove the majority of the oocysts from a pool (assuming a 6 hour turnover and good capture).

Once the pool is contaminated, the oocyst resistance to halogens and the difficulty of removing the cysts by filtration can result in pools which are contaminated for lengthy periods of time. Pool operators can reduce the risk of initial contamination by using common sense operating practices.

Additional assistance can be obtained by calling your local health department. For more specific information on this procedure, please call the Sanitary Engineering Section at (402) 444-7485.