Cryptosporidium infection (cryptosporidiosis) is an illness caused by tiny, one-celled cryptosporidium parasites. When cryptosporidia (krip-toe-spoe-RID-e-uh) enter your body, they travel to your small intestine and then burrow into the walls. Later, they're shed in your feces.

In most healthy people, a cryptosporidium infection produces a bout of watery diarrhea. The infection usually goes away within a week or two. If you have a compromised immune system, a cryptosporidium infection can become life-threatening without treatment.

You can help prevent a cryptosporidium infection by practicing good hygiene and avoiding swallowing water from pools, recreational water parks, lakes and streams.


The first signs and symptoms of cryptosporidium infection, which usually appear within a week after infection, might include:

  • Watery diarrhea
  • Dehydration
  • Lack of appetite
  • Weight loss
  • Stomach cramps or pain
  • Fever
  • Nausea
  • Vomiting

Symptoms can last for up to two weeks, though they might come and go for up to a month, even in people with healthy immune systems. Some people with cryptosporidium infection have no symptoms.

When to see a doctor

Seek medical attention if you develop watery diarrhea that does not get better within a few days.


Cryptosporidium infection begins when the one-celled cryptosporidium parasites get into your body through your mouth. Some strains of cryptosporidium can cause more serious disease.

These parasites then travel to your intestinal tract, where they settle into the walls of your intestines. Eventually, more cells are produced and are shed in massive quantities into your feces, where they are highly contagious.

You can become infected with cryptosporidia by touching anything that has come in contact with contaminated feces. You can get infected by:

  • Drinking contaminated water that contains cryptosporidium parasites
  • Swimming in contaminated water that contains cryptosporidium parasites and accidentally swallowing some of it
  • Eating uncooked, contaminated food that contains cryptosporidia
  • Touching your hand to your mouth if your hand has been in contact with a contaminated surface, object, person or animal

If you have a compromised immune system from HIV/AIDS, you're more susceptible to illness from cryptosporidium parasites than is a person with a healthy immune system. People with HIV/AIDS can develop severe symptoms and a chronic, persistent form of disease that can be difficult to treat.

Hardy parasites

Cryptosporidium parasites are one of the more common causes of infectious diarrhea in humans. This parasite is difficult to to get rid of because it's resistant to many disinfectants and many filters don't remove it.

Cryptosporidia can survive for months at varying temperatures, though the parasite can be destroyed by boiling.

Risk factors

People who are at increased risk of developing cryptosporidiosis include:

  • Children, particularly those wearing diapers, who attend child care centers
  • Parents of infected children
  • Child care workers
  • Animal handlers
  • Those who engage in oral-to-anal sexual activity
  • International travelers, especially those traveling to developing countries
  • Backpackers, hikers and campers who drink untreated, unfiltered water
  • Swimmers who swallow water in pools, lakes and rivers
  • People who drink water from shallow, unprotected wells


Complications of cryptosporidium infection include:

  • Malnutrition resulting from poor absorption of nutrients from your intestinal tract
  • Severe dehydration
  • Significant weight loss
  • Inflammation of the passage between your liver, gallbladder and small intestine (bile duct)
  • Inflammation of your gallbladder, liver or pancreas

Cryptosporidium infection isn't life-threatening. However, if you've had a transplant or if you have a weakened immune system, developing complications can be dangerous.


Cryptosporidium infection is contagious, so take precautions to avoid spreading the parasite to other people. There's no vaccine to prevent a cryptosporidium infection.

To help prevent cryptosporidium infection:

  • Practice good hygiene. Wash your hands for at least 20 seconds with soap and water after using the toilet and changing diapers, and before and after eating. Alcohol-based hand sanitizers don't kill the germs that cause cryptosporidium infection.
  • Thoroughly wash with uncontaminated water all fruits and vegetables that you will eat raw, and avoid eating food you suspect could be contaminated. If you're traveling in a developing country, avoid uncooked foods.
  • Purify drinking water if you have a weakened immune system or are traveling in an area with a high risk of infection. Methods include boiling — at least one minute at a rolling boil — or filtering, although filtering might not be as effective as boiling.

    Be sure to use a filter that meets the NSF International standard 53 or 58 requirements for cyst and oocyst reduction. You'll need a separate water filter for bacteria and viruses.

  • Avoid fecal exposure during sexual activity.

Always avoid swimming when you have diarrhea. If you know you've had a cryptosporidium infection, don't go swimming for at least two weeks after your symptoms go away because you can still be contagious.

Dec. 12, 2019
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  2. Parasites — Cryptosporidium (also known as "crypto"). General information for the public. Centers for Disease Control and Prevention. https://www.cdc.gov/parasites/crypto/general-info.html. Accessed Oct. 29, 2019.
  3. Cryptosporidiosis. Merck Manual Professional Version. https://www.merckmanuals.com/professional/infectious-diseases/intestinal-protozoa-and-microsporidia/cryptosporidiosis?query=cryptosporidiosis. Accessed Oct. 29, 2019.
  4. Pielok L, et al. Massive cryptosporidium infections and diarrhea in HIV-negative patients. Parasitology Research. 2019; doi:10.007/s00436-019-06302-0.
  5. Parasites — Cryptosporidium (also known as "crypto"). Prevention & control — General public. Centers for Disease Control and Prevention. https://www.cdc.gov/parasites/crypto/gen_info/prevention-general-public.html. Accessed Oct. 29, 2019.
  6. Leder K, et al. Treatment and prevention of cryptosporidiosis. https://www.uptodate.com/contents/search. Accessed Oct. 29, 2019.


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