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Environmental Health Division
Download a print version of this document: Cryptosporidium (PDF)
In April 1993, an intestinal parasite called Cryptosporidium was responsible for a major outbreak of illness in the city of Milwaukee, Wisconsin. More than 400,000 people became ill after drinking contaminated water from the city water supply system. Most of these people recovered on their own, but those with compromised immune systems were sometimes unable to fight off the disease. It is now believed that as many as 100 people may have died as a result of this incident.
Since that time, water systems across the country have been taking extra precautions to make sure such an incident does not occur in their communities. A variety of measures can and are being taken. Providing information is an important part of this effort. Information about this illness can help you protect yourself—and that’s especially important for people who have conditions that may compromise their immune systems. This fact sheet provides information on Cryptosporidium—what it is, what’s being done about it, and what you can do to avoid becoming ill.
Although Cryptosporidium is not new, it has been recognized as a health threat for a relatively short time—the first known cases of illness in humans date from 1976. Because of what happened in Milwaukee, increased concern has been focused on the issue. Intensive efforts have been underway to measure the risks associated with Cryptosporidium contamination in drinking water with steps being taken to reduce them, including new regulations that strengthen the requirements for public water systems using surface water as their source.
What is Cryptosporidium?
Cryptosporidium is a protozoan—a slightly more complex type of organism than a bacterium or virus. It can live in the intestines of humans or animals. Of the six known species of Cryptosporidium, Cryptosporidium parvum is thought to pose the greatest threat of human infection.
Outside of the body, Cryptosporidium is protected by an outer shell called an oocyst. Once the oocyst is consumed—in food or water—the organism can emerge from the shell and infect the lining of the intestine, causing an illness called cryptosporidiosis. The symptoms include diarrhea, nausea, vomiting, and abdominal cramping. The illness usually begins two to ten days after infection and generally lasts for no more than several weeks for people with normal immune systems. However, for people with compromised immune systems, the illness may be more persistent and more severe—even fatal. People with compromised immune systems can include those living with HIV or AIDS, as well as cancer patients receiving chemotherapy.
The principle source of Cryptosporidium contamination is believed to be animals, both domestic and wild. Cryptosporidium is relatively widespread in the environment and is commonly found in rivers and lakes—especially when the water is contaminated with animal wastes. Based on the results of national sampling and testing efforts, it is likely that some amount of Cryptosporidium contamination can probably be detected in most water supply systems—if they get their water from surface water sources (lakes, rivers, or streams) and if enough samples are taken.
What’s being done to protect our drinking water in Minnesota?
Oocysts can survive chlorine treatment, which means that Cryptosporidium resists conventional disinfection methods. The water must be filtered in order to remove Cryptosporidium. Most public water systems in Minnesota use wells to get their water from under the ground. These groundwater systems have a built-in advantage in the fight against Cryptosporidium: the ground itself serves as a natural filter as the water percolates from the surface down to the aquifer.
Twenty-four community water systems and approximately 60 noncommunity water systems in Minnesota use surface water as their source of drinking water. Surface water is open to the environment and more susceptible to contamination. However, all surface water systems in Minnesota use filtration—which removes Cryptosporidium—as part of the treatment process. Monitoring requirements must be met, and the water system must be operating at optimum levels at all times so that a breakdown does not occur at this critical point in the treatment process.
There are new regulations in place for public water systems that use a surface water source. These regulations aim to improve public health protection through the control of microbial contaminants by focusing on systems with elevated Cryptosporidium risk. To determine if a surface water source is vulnerable to contamination, surface water systems are required to monitor their source water for Cryptosporidium. Based on the annual average of these results, additional treatment may be required. However, due to the high cost of Cryptosporidium analysis, surface water systems serving less than 10,000 people are eligible to conduct E. coli monitoring in lieu of Cryptosporidium monitoring. If the annual average of the E. coli results exceeds specific trigger levels, then Cryptosporidium monitoring will be required to determine if additional treatment is required.
The Minnesota Department of Health (MDH) is one of only four sites in the United States chosen to participate in a federally funded Emerging Infections Program. As part of this program, MDH is conducting surveillance for cryptosporidiosis so that if outbreaks occur, they can be detected early.
Treatment systems follow a multi-barrier approach in dealing with Cryptosporidium
It’s important to remember that monitoring for Cryptosporidium (or E. Coli) will detect pathogens only after they are already present. For that reason, system operators need to make sure their treatment facilities are functioning efficiently and effectively at all times.
To protect against Cryptosporidium and other waterborne diseases, the public water systems use a multi-part strategy that includes:
- protecting the source water and supporting watershed management efforts.
- using the most effective possible treatment methods.
- making sure the water distribution system is properly maintained.
- conducting the required water quality monitoring for the treated water and the distribution system.
What you can do to protect yourself
People with compromised immune systems may want to consult with their clinicians and consider special precautions, such as those listed below, any time there are questions regarding the safety of their drinking water.
Boiling the water for one minute (and allowing it to cool before drinking) is the best extra measure that can be taken to make sure water is free of Cryptosporidium and any other germs. People should also avoid drinking or accidentally swallowing water from rivers, lakes, streams, or swimming pools. People with compromised immune systems should avoid swimming in rivers, lakes, and perhaps even swimming pools (oocysts are not killed by chlorine) since accidental water ingestion often occurs with swimming.
Alternatives to boiling water include switching to bottled water or installing point-of-use water treatment devices. Bottled water is subject to fewer regulatory safeguards than water from your public water supply system, however, and its quality can vary. Unless it has been distilled or pasteurized, bottled water may not be any safer than tap water. If the bottling company gets its water from a properly designed and operated groundwater system, it’s unlikely that there will be any Cryptosporidium in the water.
Point-of-use filters are effective against Cryptosporidium if they are capable of removing particles one micrometer or less in diameter. Also, devices that use ultraviolet technology are effective for inactivating the organism. When selecting a treatment system for the removal of Cryptosporidium, be sure to select a device that is ANSI/NSF certified for the technology being used. Also, when using any type of treatment device, it is important to maintain it properly and when using a filtration device, change the filters at regular intervals. Failing to maintain a treatment unit will reduce its effectiveness and may even make contamination problems worse.
For more information:
Contact the Minnesota Department of Health Drinking Water Protection Section at 651-201-4700.