Cryptosporidium: A Risk to Our Drinking Water

In April 1993 thousands of Milwaukee residents and visitors were stricken with a flu-like illness caused by a tiny yet potent protozoan called Cryptosporidium.

The outbreak sickened 403,000 people and was linked to inadequate treatment of drinking water taken from Lake Michigan. No specific source of the cryptosporidium was ever identified but runoff from abnormally heavy spring rains most likely carried the crypto to the lake from a variety of sources.

Table of contents

1. Where does crypto come from?
2. What does crypto do to you?
3. Can cryptosporidium be spread other than by drinking water?
4. How is crypto detected?
5. How is crypto removed from drinking water?
6. What public health steps are being taken to avoid another "Milwaukee"?
7. What can people do to protect themselves from crypto?
8. Where to call for more information not covered in this presentation

Where does crypto come from?

Cryptosporidium (pronounced krip'-toe-spore-rid'-ee-um) is a one-celled protozoan found in the environment as an oocyst (oh'-a-sist). An oocyst is a dormant form of the organism about two to six microns in diameter. Oocysts are too tiny to see without a microscope. The oocysts are very tough and can withstand all kinds of environmental extremes.

Cryptosporidium is commonly found in rivers, lakes and streams contaminated with animal feces or which receive wastewater from sewage treatment plants. Cattle, especially calves, seem to be a major source of Cryptosporidium.

Researchers have found Cryptosporidium levels of 5,000 oocysts per liter in raw sewage; 1,000 oocysts per liter in treated wastewater; and two to 112 oocysts per liter in several western U.S. rivers. A 1991 national study found Cryptosporidium in 87 percent of untreated drinking water and 27 percent of treated drinking water taken from rivers or lakes.

Water from public and private wells usually doesn't contain these protozoans as long as the well is properly constructed and maintained to prevent runoff from entering the well.

What does crypto do to you?

Cryptosporidiosis is the disease humans develop when Cryptosporidium oocysts enter the body through contaminated drinking water or in other ways. Symptoms may last seven or more days and include diarrhea, stomach cramps, nausea, fatigue, dehydration and headaches.

In normal healthy people cryptosporidiosis is self limiting, meaning that the body's immune system will eventually defeat the infection. But, cryptosporidiosis can last longer and become life-threatening in people whose immune systems are weakened by cancer chemotherapy or AIDs.

Can cryptosporidium be spread other than by drinking water?

Newly-formed Cryptosporidium oocysts are shed in feces and are infectious to others. To prevent transmitting cryptosporidiosis to others, infected people should thoroughly wash their hands after using the toilet, especially while ill with cryptosporidiosis and for two weeks after diarrhea stops. Good hygiene is a must to prevent exposure to Cryptosporidium as well as other disease-causing organisms and germs.

How is crypto detected?

Detecting Cryptosporidium in drinking water requires sampling a large volume of water because the organisms usually are widely distributed. The current standard method of detecting crypto is to pipe rom 500 to 1,000 gallons of water through a filter with openings less than one micron in size to collect any fine particles and protozoans that are present.

The material collected on the filter is removed and examined using special techniques to find Cryptosporidium oocysts. Testing is slow and expensive, costing about $300 a sample. Researchers are working on developing faster, less expensive procedures to make detection easier in the future.

How is crypto removed from drinking water?

What Water Utilities Can Do to Minimize Public Exposure to Cryptosporidium in Drinking Water

Treating drinking water using normal doses of disinfectants such as chlorine does not kill Cryptosporidium oocysts. Researchers have found it takes 90 minutes to kill 90 percent of Cryptosporidium oocysts in a water sample treated with 80 milligrams of chlorine per liter of water. Normally, chlorine is applied at about one milligram per liter. Stronger disinfectants, such as ozone, do a better job of killing these protozoans in a shorter time.

All water systems using rivers or lakes as sources of drinking water must treat the water before distributing it to customers. Typical treatment steps involve adding substances to water pumped into the treatment plant to coagulate particles suspended in the incoming water. The coagulated particles are allowed to settle out. The remaining water is then filtered to remove even more particles, disinfected and piped to customers.

What public health steps are being taken to avoid another incident like Milwaukee?

Milwaukee's outbreak of cryptospordiosis has shown that more effective ways to remove or inactivate Cryptosporidium in water are needed.

When the usual treatment steps fail, the state Department of Natural Resources and local officials will advise water customers to boil for five minutes any tap water customers plan to use as drinking water or for cooking or washing food. In these situations officials will also test the water supply to find any Cryptosporidium that may be present.

Another safeguard that took effect in June 1993 is new, more restrictive federal requirements for turbidity (cloudiness) in treated drinking water. Treatment plant operators must test more often for turbidity as well as meet a more stringent standard for turbidity.

The impact of the standard will not totally prevent Cryptosporidium from becoming a problem in drinking water, but it will give officials faster notice of problems so other steps can be taken to protect public health from this troublesome protozoan.

What can people do to protect themselves from crypto?

Much more needs to be learned about keeping drinking water safe from Cryptosporidium, and research is underway. Here's what you can do:

• Ask your local drinking water supplier about drinking water quality in your area.
• Practice good personal hygiene and make sure your family does, too.
• Support programs to improve drinking water quality.