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Home>Water University>Water Contaminants>Cryptosporidium Cysts

Cryptosporidium Cysts

This is a fact sheet about a contaminant that may be found in some public or private drinking water supplies. It may cause health problems if found in amounts greater than the health standard set by the United States Environmental Protection Agency (EPA).


Cryptosporidium is a parasite that enters lakes and rivers through sewage and animal waste. It causes cryptosporidiosis, a mild gastrointestinal disease. However, the disease can be severe or fatal for people with severely weakened immune systems. EPA and CDC have prepared advice for those with severely compromised immune systems who are concerned about Cryptosporidium.

Cryptosporidium is very resistant to disinfection, and even a well-operated water treatment system cannot ensure that drinking water will be completely free of this parasite. Current EPA drinking water standards were not explicitly designed to assure the removal or killing of Cryptosporidium. Many large water systems already voluntarily take actions for greater control of Cryptosporidium and other microbial contaminants. By 2001, the water systems serving the majority of the United States population (those relying on a surface water source, such as a river, and serving more than 10,000 people) must meet a new EPA standard that strengthens control over microbial contaminants, including Cryptosporidium. EPA continues to conduct research on microbial contaminants which will be used for determining priorities for the drinking water program, including setting future standards and reevaluating existing standards.

Cryptosporidium has caused several large waterborne disease outbreaks of gastrointestinal illness, with symptoms that include diarrhea, nausea, and/or stomach cramps. People with severely weakened immune systems (that is, severely immunocompromised) are likely to have more severe and more persistent symptoms than healthy individuals. Moreover, Cryptosporidium has been a contributing cause of death in some immunocompromised people. Individuals who are severely immunocompromised may include those who are infected with HIV/AIDS, cancer and transplant patients taking immunosuppressive drugs, and people born with a weakened immune system.


Data are not adequate to determine how most people become infected. For example, we do not know the importance of drinking water compared to other possible sources of Cryptosporidium, such as exposure to the feces of infected persons or animals, eating contaminated food, or accidentally swallowing contaminated recreational water.

Thus, in the absence of an outbreak, there are insufficient data to determine whether a severely immunocompromised individual is at a noticeably greater risk than the general public from waterborne Cryptosporidiosis. Even a low level of Cryptosporidium in water, however, may be of concern for the severely immunocompromised, because the illness can be life-threatening. The risk of a severely immunocompromised individual acquiring Cryptosporidiosis from drinking water in the absence of an outbreak is likely to vary from city to city, depending on the quality of the city's water source and the quality of water treatment. Current risk data are not adequate to support a recommendation that severely immunocompromised persons in all U.S. cities boil or avoid drinking tap water.

In the absence of a recognized outbreak, this guidance has been developed for severely immunocompromised people who may wish to take extra precautions to minimize their risk of infection from waterborne Cryptosporidiosis. To be effective, the guidance must be followed consistently for all water used for drinking or for mixing beverages. During outbreaks of waterborne Cryptosporidiosis, studies have found that people who used precautions only part of the time were just as likely to become ill as people who did not use them at all.

Further Information:

When an outbreak of waterborne Cryptosporidiosis is recognized and is determined to be on-going, officials of the public-health department and/or the water utility will normally issue a "boil water" notice to protect both the general public and the immunocompromised.

Current testing methods cannot determine with certainty whether Cryptosporidium detected in drinking water is alive or whether it can infect humans. In addition, the current method often requires several days to get results, by which time the tested water has already been used by the public and is no longer in the community's water pipes.

Severely immunocompromised people may face a variety of health risks. Depending on their illness and circumstances, a response by such individuals that focuses too specifically on one health risk may decrease the amount of attention that should be given to other risks. Health care providers can assist severely immunocompromised persons in weighing these risks and in applying this guidance.

What is cryptosporidiosis?

Cryptosporidiosis is a diarrheal disease caused by microscopic parasites of the genus Cryptosporidium. Once an animal or person is infected, the parasite lives in the intestine and passes in the stool. The parasite is protected by an outer shell that allows it to survive outside the body for long periods of time and makes it very resistant to chlorine- based disinfectants. Both the disease and the parasite are commonly known as "crypto."

During the past two decades, crypto has become recognized as one of the most common causes of waterborne disease within humans in the United States. The parasite may be found in drinking water and recreational water in every region of the United States and throughout the world.

How is cryptosporidiosis spread?

Cryptosporidium lives in the intestine of infected humans or animals. Millions of crypto germs can be released in a bowel movement from an infected human or animal. Consequently, Cryptosporidium is found in soil, food, water, or surfaces that have been contaminated with infected human or animal feces. If a person swallows the parasite they become infected. You cannot become infected through contact with blood. The parasite can be spread by;

Accidentally putting something into your mouth or swallowing something that has come into contact with feces of a person or animal infected with Cryptosporidium.

Swallowing recreational water contaminated with Cryptosporidium (Recreational water includes water in swimming pools, hot tubs, jacuzzis, fountains, lakes, rivers, springs, ponds, or streams that can be contaminated with sewage or feces from humans or animals.) Note: Cryptosporidium can survive for days in swimming pools with adequate chlorine levels.

Eating uncooked food contaminated with Cryptosporidium. Thoroughly wash with clean, safe water all vegetables and fruits you plan to eat raw. See below for information on making water safe.

Accidentally swallowing Cryptosporidium picked up from surfaces (such as bathroom fixtures, changing tables, diaper pails, or toys) contaminated with feces from an infected person.

What are the symptoms of cryptosporidiosis?

The most common symptom of cryptosporidiosis is watery diarrhea. Other symptoms include:
Weight loss
Stomach cramps or pain

Some people with crypto will have no symptoms at all. While the small intestine is the site most commonly affected , Cryptosporidium infections could possibly affect other areas of the digestive or the respiratory tract .

How long after infection do symptoms appear?

Symptoms of cryptosporidiosis generally begin 2 to 10 days (average 7 days) after becoming infected with the parasite.

How long will symptoms last?

In persons with healthy immune systems, symptoms usually last about 1 to 2 weeks. The symptoms may go in cycles in which you may seem to get better for a few days, then feel worse again before the illness ends.

If I have been diagnosed with Cryptosporidium , should I worry about spreading the infection to others?

Yes, Cryptosporidium can be very contagious. Follow these guidelines to avoid spreading the disease to others:

Wash your hands with soap and water after using the toilet, changing diapers, and before eating or preparing food.

Do not swim in recreational water (pools, hot tubs, lakes or rivers, the ocean, etc.) if you have cryptosporidiosis and for at least 2 weeks after diarrhea stops. You can pass Cryptosporidium in your stool and contaminate water for several weeks after your symptoms have ended. This has resulted in outbreaks of cryptosporidiosis among recreational water users.

Note: Cryptosporidium can be spread in a chlorinated pool because it is resistant to chlorine and, therefore, can live for days in chlorine-treated swimming pools.

Who is most at risk for cryptosporidiosis?

People who are most likely to become infected with Cryptosporidium include:
Children who attend day care centers, including diaper-aged children
Child care workers.
Parents of infected children.
International travelers.
Backpackers, hikers, and campers who drink unfiltered, untreated water.
Swimmers who swallow water while swimming in swimming pools, lakes, rivers, ponds, and streams.
People who drink from shallow, unprotected wells.
People who swallow water from contaminated sources.

Contaminated water includes water that has not been boiled or filtered. Several community-wide outbreaks of cryptosporidiosis have been linked to drinking municipal water or recreational water contaminated with Cryptosporidium.

Who is most at risk for getting seriously ill with cryptosporidiosis?

Although Crypto can infect all people, some groups are more likely to develop more serious illness.

Young children and pregnant women may be more susceptible to the dehydration resulting from diarrhea and should drink plenty of fluids while ill.

If you have a severely weakened immune system, you are at risk for more serious disease. Your symptoms may be more severe and could lead to serious or life-threatening illness. Examples of persons with weakened immune systems include those with HIV/AIDS; cancer and transplant patients who are taking certain immunosuppressive drugs; and those with inherited diseases that affect the immune system.

What should I do if I think I may have cryptosporidiosis?

If you suspect that you have cryptosporidiosis, see your health care provider.

How is a cryptosporidiosis diagnosed?

Your health care provider will ask you to submit stool samples to see if you are infected. Because testing for Crypto can be difficult, you may be asked to submit several stool specimens over several days. Tests for Crypto are not routinely done in most laboratories; therefore, your health care provider should specifically request testing for the parasite.

What is the treatment for cryptosporidiosis?

A new drug, nitazoxanide, has been approved for treatment of diarrhea caused by Cryptosporidium in people with healthy immune systems. Consult with your health care provider for more information. Most people who have a healthy immune system will recover without treatment. The symptoms of diarrhea can be treated. If you have diarrhea, drink plenty of fluids to prevent dehydration. Rapid loss of fluids from diarrhea may be especially life threatening to babies; therefore, parents should talk to their health care provider about fluid replacement therapy options for infants. Anti-diarrheal medicine may help slow down diarrhea, but talk to your health care provider before taking it.

People who are in poor health or who have a weakened immune system are at higher risk for more severe and more prolonged illness. The effectiveness of nitazoxanide in immunosuppressed individuals is unclear. For persons with AIDS, anti-retroviral therapy that improves immune status will also decrease or eliminate symptoms of Crypto. However, even if symptoms disappear, cryptosporidiosis is usually not curable and the symptoms may return if the immune status worsens. See your health care provider to discuss anti-retroviral therapy used to improve your immune status.

How can I prevent cryptosporidiosis?

Practice good hygiene.
Wash hands thoroughly with soap and water.
Wash hands after using the toilet and before handling or eating food (especially for persons with diarrhea).
Wash hands after every diaper change, especially if you work with diaper-aged children, even if you are wearing gloves.
Protect others by not swimming if you are experiencing diarrhea (essential for children in diapers).

Avoid water that might be contaminated.
Do not swallow recreational water.
Do not drink untreated water from shallow wells, lakes, rivers, springs, ponds, and streams.
Do not drink untreated water during community-wide outbreaks of disease caused by contaminated drinking water.
Do not use untreated ice or drinking water when traveling in countries where the water supply might be unsafe.

In the United States , nationally distributed brands of bottled or canned carbonated soft drinks are safe to drink. Commercially packaged non-carbonated soft drinks and fruit juices that do not require refrigeration until after they are opened (those that are stored unrefrigerated on grocery shelves) also are safe.

If you are unable to avoid using or drinking water that might be contaminated, then you can make the water safe to drink by doing one of the following:
Heat the water to a rolling boil for at least 1 minute.
Use a filter that has an absolute pore size of at least 1 micron or one that has been NSF rated for "cyst removal."

Do not rely on chemicals to disinfect water and kill Cryptosporidium. Because it has a thick outer shell, this particular parasite is highly resistant to disinfectants such as chlorine and iodine.

Avoid food that might be contaminated.
Wash and/or peel all raw vegetables and fruits before eating.
Use safe, uncontaminated water to wash all food that is to be eaten raw.
Avoid eating uncooked foods when traveling in countries with minimal water treatment and sanitation systems.

Take extra care when traveling.
If you travel to developing nations, you may be at a greater risk for Cryptosporidium infection because of poorer water treatment and food sanitation. Warnings about food, drinks, and swimming are even more important when visiting developing countries. Avoid foods and drinks, in particular raw fruits and vegetables, tap water, or ice made from tap water, unpasteurized milk or dairy products, and items purchased from street vendors. These items may be contaminated with Cryptosporidium. Steaming-hot foods, fruits you peel yourself, bottled and canned processed drinks, and hot coffee or hot tea are probably safe. Talk with your health care provider about other guidelines for travel abroad.

Preventing Cryptosporidiosis:

A Guide to Water Filters and Bottled Water

Filtering tap water: Many, but not all available home water filters remove Cryptosporidium. Some filter designs are more suitable for removal of Cryptosporidium than others. Filters that have the words "reverse osmosis" on the label protect against Cryptosporidium. Many other types of filters that work by micro-straining also work. Look for a filter that has a pore size of 1 micron or less. This will remove microbes 1 micron or greater in diameter (Cryptosporidium, Giardia). There are two types of these "absolute 1 micron" filters and "nominal 1 micron" filters. The absolute 1 micron filter will more consistently remove Cryptosporidium than a nominal filter. Some nominal 1 micron filters will allow 20% to 30% of 1 micron particles to pass through.

NSF-International (NSF) does independent testing of filters to determine if they remove Cryptosporidium. To find out if a particular filter is certified to remove Cryptosporidium, you can look for the NSF trademark plus the words "cyst reduction" or "cyst removal" on the product label information. You can also contact the NSF at 789 N. Dixboro Road, Ann Arbor, MI 48105 USA, toll free1-877-867-3435, fax 313-769-0109, email info@nsf.org, or visit their Web site at www.nsf.org/certified/DWTU/. At their Web site, you can enter the model number of the unit you intend to buy to see if it is on their certified list, or you can look under the section entitled "Reduction claims for drinking water treatment units - Health Effects" and check the box in front of the words "Cyst Reduction." This will display a list of filters tested for their ability to remove Cryptosporidium.

Because NSF testing is expensive and voluntary, some filters that may work against Cryptosporidium have not been NSF-tested. If you chose to use a product not NSF-certified, select those technologies more likely to reduce Cryptosporidium, this includes filters with reverse osmosis and those that have an absolute pore size of 1 micron or smaller.

Note: Filters collect germs from water, so someone who is not HIV infected or immune impaired should change the filter cartridges. Anyone changing the cartridges should wear gloves and wash hands afterwards. Filters may not remove Cryptosporidium as well as boiling does because even good brands of filters may sometimes have manufacturing flaws that allow small numbers of Cryptosporidium to get in past the filter. Selection of NSF-Certified filters provides additional assurance against such flaws. Also, poor filter maintenance or failure to replace the filter cartridges as recommended by the manufacturer can cause a filter to fail.

Bottled water: Labels reading "well water," "artesian well water," "spring water," or "mineral water" do not guarantee that the water does not contain crypto. However, water that comes from protected well or protected spring water sources is less likely to contain crypto than bottled water or tap water from less protected sources, such as rivers and lakes.

Home distillers: You can remove crypto and other germs from your water with a home distiller. If you use one, you need to carefully store your water as recommended for storing purified water.

Other drinks: Soft drinks and other beverages may or may not contain crypto. You need to know how they were prepared to know if they might contain crypto.

Crypto killed or removed in preparation Crypto may not be killed or removed in preparation
Canned or bottled soda, seltzer, and fruit drinks Fountain drinks
Steaming hot (175 degrees F or hotter) tea or coffee Fruit drinks you mix with tap water from frozen concentrate
Pasteurized drinks Iced tea or coffee

Juices made from fresh fruit can also be contaminated with crypto. Several people became ill after drinking apple cider made from apples contaminated with crypto. You may wish to avoid unpasteurized juices or fresh juices if you do not know how they were prepared.

Note: This fact sheet is part of a larger publication adapted from U.S. CDC publication: Center for Disease Control Division of Parasitic Diseases and U.S. EPA publication: EPA National Primary Drinking Water Regulations..

This fact sheet is for information only and is not meant to be used for self-diagnosis or as a substitute for consultation with a health care provider. If you have any questions about the disease described above or think that you may have a parasitic infection, consult a health care provider.