People acquire the infection by consuming contaminated water or food or by having contact with infected people or animals.
Abdominal cramping and watery diarrhea may begin suddenly, sometimes accompanied by nausea, vomiting, fever, and weakness.
Doctors diagnose the infection by examining or analyzing a stool sample for signs of the parasite.
Adequate sanitation and hand washing can help prevent spread of the infection, as can boiling water before drinking it.
Healthy people often recover on their own, but they may require treatment with an antiparasitic drug.
People with AIDS Human Immunodeficiency Virus (HIV) Infection Human immunodeficiency virus (HIV) infection is a viral infection that progressively destroys certain white blood cells and is treated with antiretroviral medications. If untreated, it can cause... read more
or a weakened immune system Overview of Immunodeficiency Disorders Immunodeficiency disorders involve malfunction of the immune system, resulting in infections that develop and recur more frequently, are more severe, and last longer than usual. Immunodeficiency... read more may continue to have diarrhea even after they have been treated with an antiparasitic drug.
(See also Overview of Parasitic Infections Overview of Parasitic Infections A parasite is an organism that lives on or inside another organism (the host) and benefits (for example, by getting nutrients) from the host at the host's expense. Although this definition actually... read more .)
Cryptosporidium parasites are protozoa that infect people and many kinds of animals throughout the world.
Cryptosporidiosis is acquired by
Ingesting Cryptosporidium parasites in water or food contaminated by human or animal feces containing the parasite's eggs
Ingesting parasites from soil or an item that has been contaminated with eggs
Ingesting parasites acquired from close contact with an infected person or animal
The thick-walled eggs of Cryptosporidium are very hardy and are frequently present in swimming pools, hot tubes, water parks, lakes, and rivers around the world. The parasite is not killed by freezing or by the usual levels of chlorine in swimming pools or drinking water.
After people swallow the eggs, the eggs move to the intestine, where they release an immature form of the parasite, which enters the cells that line the intestine. The parasite matures, multiplies, and produces eggs. People then pass the eggs in their feces. Only a small number of Cryptosporidium eggs are required to cause infection. Because of the enormous number of Cryptosporidium that an infected person or animal can shed (10 million to 100 million) in their stool and the ability of just a few ingested organisms to start an infection, the infection can easily spread person-to-person, for example, in day care centers or petting zoos.
Cryptosporidiosis is a common cause of diarrhea among children living in areas where sanitation is poor. It occasionally occurs among travelers to such areas. Cryptosporidiosis also causes diarrhea outbreaks in the United States. In Baker City, Oregon, 2,780 people became sick when the city's water supply was contaminated with Cryptosporidium in 2013. Outbreaks have occurred in other cities and in day care centers.
People with a weakened immune system Overview of Immunodeficiency Disorders Immunodeficiency disorders involve malfunction of the immune system, resulting in infections that develop and recur more frequently, are more severe, and last longer than usual. Immunodeficiency... read more , particularly those with advanced AIDS More severe symptoms Human immunodeficiency virus (HIV) infection is a viral infection that progressively destroys certain white blood cells and is treated with antiretroviral medications. If untreated, it can cause... read more , are prone to cryptosporidiosis and are more likely to have severe, persistent disease.
Symptoms of Cryptosporidiosis
Cryptosporidiosis symptoms may begin abruptly about 7 days after people are infected and consist mainly of abdominal cramps and watery diarrhea. Nausea, vomiting, loss of appetite, fever, and weakness may also occur. Symptoms usually last 1 to 2 weeks, then subside. People may pass eggs in their stool for several weeks after symptoms have disappeared.
In people with a weakened immune system, symptoms of cryptosporidiosis may begin gradually, and the diarrhea can vary from mild to severe (as much as 3 to 4 gallons [11 to 15 liters] of watery stool per day in people with AIDS) and may persist for a long time.
Cryptosporidiosis is also associated with undernutrition Undernutrition Undernutrition is a deficiency of calories or of one or more essential nutrients. Undernutrition may develop because people cannot obtain or prepare food, have a disorder that makes eating or... read more 
in children living in areas with poor sanitation.
Diagnosis of Cryptosporidiosis
Stool tests
To diagnose cryptosporidiosis, a doctor sends a stool sample to be tested for a protein released by the parasite (antigen testing) or for the parasite's genetic material (DNA).
Another approach is to examine stool under a microscope for Cryptosporidium eggs, but this method is less sensitive, and several stool samples may be needed to find the parasite. Specialized techniques can be used to increase the chances of identifying the eggs.
Doctors may use a flexible viewing tube (endoscope Endoscopy Endoscopy is an examination of internal structures using a flexible viewing tube (endoscope). In addition to examinations, doctors can use endoscopy to do biopsies and give treatment. Endoscopes... read more ) to examine the upper part of digestive tract, including the first part of the small intestine (duodenum), when diagnostic tests of stool do not identify a cause for persistent diarrhea. Doctors may use this procedure to obtain a sample of tissue to be examined and analyzed (biopsied). Cryptosporidium, if present, can be seen in a biopsy sample from the intestine.
Prevention of Cryptosporidiosis
Cryptosporidiosis prevention involves adequate sanitation and hand washing, particularly in health care facilities and day care centers and after contact with soil, animals, or infected people. People should not drink or swallow water that could be contaminated, such as that from a swimming pool, hot tub, water park, stream, river, lake or ocean, or tap water during international travel to areas where sanitation is poor. Safer sex practices are important in preventing infection from anal contact.
When public health departments discover a localized outbreak of the disease, they typically advise people to
Boil drinking water (including water for toothbrushing and food washing)
Eat only cooked foods
Avoid unpasteurized milk and juice
Tap water filters that use reverse osmosis or have the words "tested and certified by NSF/ANSI Standard No. 53 or No. 58 for cyst removal/reduction" are likely to be effective. Other types of filters may not be.
Treatment of Cryptosporidiosis
For people with a normal immune system Overview of the Immune System The immune system is designed to defend the body against foreign or dangerous invaders. Such invaders include Microorganisms (commonly called germs, such as bacteria, viruses, and fungi) Parasites... read more and severe or persistent diarrhea, treatment is with nitazoxanide
For people with AIDS More severe symptoms Human immunodeficiency virus (HIV) infection is a viral infection that progressively destroys certain white blood cells and is treated with antiretroviral medications. If untreated, it can cause... read more
, treatment of the HIV infection, plus sometimes nitazoxanide to help relieve symptomsIf diarrhea is severe, fluids and an antidiarrheal drug
People with a healthy immune system typically recover on their own. If such people have severe or persistent diarrhea, nitazoxanide (an antiparasitic drug) may help speed recovery.
Nitazoxanide does not cure cryptosporidiosis in people who have AIDS. The most important therapy is to treat the HIV infection Antiretroviral Treatment of Human Immunodeficiency Virus (HIV) Infection Antiretroviral medications used to treat human immunodeficiency virus (HIV) infection aim to do the following: Reduce the amount of HIV RNA (viral load) in the blood to an undetectable amount... read more (with antiretroviral drugs). When such treatment strengthens the weakened immune system, diarrhea is usually reduced. While nitazoxanide does not cure cryptosporidiosis in people with AIDS, it may decrease diarrhea and other symptoms. Doctors may also try paromomycin, or a combination of paromomycin and azithromycin, to help decrease symptoms.
It is not clear how effective nitazoxanide is in people with other causes of a weakened immune system Overview of Immunodeficiency Disorders Immunodeficiency disorders involve malfunction of the immune system, resulting in infections that develop and recur more frequently, are more severe, and last longer than usual. Immunodeficiency... read more , but it may help some people. Unless the immune system problem is corrected, diarrhea may continue throughout life. People with severe diarrhea may require treatment with fluids, given by mouth or by vein, and antidiarrheal drugs such as loperamide. However, loperamide may not help people with AIDS.
Select Medical Literature
1. Gharpure R, Perez A, Miller AD, et al: Cryptosporidiosis Outbreaks—United States, 2009-2017. MMWR Morb Mortal Wkly Rep 68:568-72, 2019.
2. Pantenburg B, Cabada MM, White AC Jr: Treatment of cryptosporidiosis. Expert Rev Anti Infect Ther 7(4):385-91, 2009. doi: 10.1586/eri.09.24
