Cryptosporidium has recently been recognized as a cause of diarrhea worldwide in all age groups. It has a greater effect on people with a weakened immune system, including:

• People who take medicines to suppress their immune system
• People with HIV/AIDS
• Transplant recipients

In these groups, this infection is not just bothersome, but can lead to severe and life-threatening loss of muscle and body mass (wasting) and malnutrition.

The major risk factor is drinking water contaminated with stool (feces). People at higher risk include:

• Animal handlers
• People who are in close contact with infected people
• Young children

Outbreaks have been linked to:

• Drinking from contaminated public water supplies
• Drinking unpasteurized cider
• Swimming in contaminated pools and lakes

Some outbreaks have been very large.

Symptoms of infection include:

• Abdominal cramping
• Diarrhea, which is often watery, non-bloody, large-volume, and occurs many times a day
• General sick feeling (malaise)
• Malnutrition and weight loss (in severe and prolonged cases)
• Nausea

These tests may be done:

• Antibody test to see if cryptosporidium is in the stool
• Intestinal biopsy (rare)
• Stool exam with special techniques (AFB staining)
• Stool exam using a microscope to look for the parasites and their eggs

There are several treatments for cryptosporidium enteritis.

The best approach is to improve immune function in people who have a weakened immune system. In people with HIV/AIDS, this can be done by using HIV-antiviral medicines. Using this type of treatment can lead to a complete remission of cryptosporidium enteritis.

Medicines such as nitazoxanide have been used in children and adults. Other medicines that are sometimes used include:

• Nitazoxanide
• Paromomycin

These medicines often help only for a little while. It is common for the infection to return.

In healthy people, the infection will clear up, but it can last up to a month. In people with a weakened immune system, long-term diarrhea may cause weight loss and malnutrition.

These complications can occur:

• Inflammation of a bile duct
• Inflammation of the gallbladder
• Inflammation of the liver (hepatitis)
• Malabsorption (not enough nutrients being absorbed from the intestinal tract)
• Inflammation of the pancreas (pancreatitis)
• Loss of body mass that causes extreme thinness and weakness (wasting syndrome)

Contact your health care provider if you develop watery diarrhea that does not go away within a few days, especially if you have a weakened immune system.

Proper sanitation and hygiene, including handwashing, are important measures for preventing this illness.

Certain water filters can also reduce risk by filtering out the cryptosporidium eggs. However, the pores of the filter must be smaller than 1 micron to be effective. If you have a weakened immune system, ask your provider if you need to boil your water.

Cryptosporidiosis

Huston CD. Intestinal protozoa. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 11th ed. Philadelphia, PA: Elsevier; 2021:chap 113.

Warren CA, Lima AAM. Cryptosporidiosis. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 321.

White AC. Cryptosporidiosis (Cryptosporidium species). In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 282.

Updated by: Jatin M. Vyas, MD, PhD, Associate Professor in Medicine, Harvard Medical School; Associate in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.