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Sources of Infection & Risk Factors

Crypto lives in the intestine of infected humans or animals. An infected person or animal sheds Cryptosporidium parasites in the stool. Millions of Crypto parasites can be released in a bowel movement from an infected human or animal. Shedding begins when the symptoms begin and can last for weeks after the symptoms (e.g., diarrhea) stop. You can become infected after accidentally swallowing the parasite. Crypto may be found in soil, food, water, or surfaces that have been contaminated with the feces from infected humans or animals. Crypto is not spread by contact with blood. Crypto can be spread by:

  • Putting something in your mouth or accidentally swallowing something that has come in contact with the stool of a person or animal infected with Crypto.
  • Swallowing recreational water contaminated with Crypto. Recreational water can be contaminated with sewage or feces from humans or animals.
  • Swallowing water or beverages contaminated by stool from infected humans or animals.
  • Eating uncooked food contaminated with Crypto. All fruits and vegetables you plan to eat raw should be thoroughly washed with uncontaminated water.
  • Touching your mouth with contaminated hands. Hands can become contaminated through a variety of activities, such as:
    • touching surfaces (e.g., toys, bathroom fixtures, changing tables, diaper pails) that have been contaminated by stool from an infected person,
    • changing diapers,
    • caring for an infected person, and
    • handling an infected animal such as a cow or calf.

People with greater exposure to contaminated materials are more at risk for infection, such as:

  • Children who attend childcare centers, including diaper-aged children
  • Childcare workers
  • Parents of infected children
  • People who take care of other people with cryptosporidiosis
  • International travelers
  • Backpackers, hikers, and campers who drink unfiltered, untreated water
  • People who drink from untreated shallow, unprotected wells
  • People, including swimmers, who swallow water from contaminated sources
  • People who handle infected cattle
  • People exposed to human feces through sexual contact

Contaminated water may include water that has not been boiled or filtered, as well as contaminated recreational water sources. Several community-wide outbreaks of cryptosporidiosis have been linked to drinking municipal water or recreational water contaminated with Cryptosporidium.

Cryptosporidium parasites are found in every region of the United States and throughout the world. Travelers to developing countries may be at greater risk for infection because of poorer water treatment and food sanitation, but cryptosporidiosis occurs worldwide. In the United States, an estimated 748,000 cases of cryptosporidiosis occur each year[1].

Once infected, people with decreased immunity are most at risk for severe disease. The risk of developing severe disease may differ depending on each person's degree of immune suppression.

  1. Scallan E, Hoekstra RM, Angulo FJ, Tauxe RV, Widdowson MA, Roy SL, Jones JL, Griffin PM. Foodborne illness acquired in the United States--major pathogens. Emerg Infect Dis. 2011;17(1):7-15.