Cryptosporidium (Human)

Primary reference(s)

WHO, 2013. Preventing cryptosporidiosis: the need for safe drinking water. World Health Organization (WHO). Accessed 28 September 2020.

Additional scientific description

Cryptosporidiosis is a disease that causes watery diarrhoea. It is caused by microscopic germs – parasites called Cryptosporidium. Both the parasite and the disease are commonly known as ‘Crypto’ (CDC, 2017). Although cryptosporidiosis can affect all people, some groups are likely to develop more serious illness. For people with weakened immune systems, symptoms can be severe and could lead to serious or life-threatening illness. Approximately 20 species of Cryptosporidium infect animals, some of which also infect humans. The parasite is protected by an outer shell that allows it to survive outside the body for long periods and makes it very resistant to chlorine disinfection (CDC, 2017). 

Symptoms of cryptosporidiosis generally begin two to ten days (average seven days) after becoming infected with the parasite. They include watery diarrhoea (the most common symptom), stomach cramps or pain, dehydration, nausea, vomiting, fever and weight loss. Some people can shed Cryptosporidiosia despite being asymptomatic (CDC, 2017). 

Symptoms usually last about one to two weeks (with a range of a few days to a month or more) in persons with healthy immune systems. Occasionally, people may experience a recurrence of symptoms after a brief period of recovery before the illness ends. Symptoms can come and go for up to 30 days.

While the small intestine is the site most commonly affected, in immunocompromised persons Cryptosporidium infections may also affect other areas of the digestive or respiratory tract. The risk of developing a severe disease may differ depending on each person’s degree of immune suppression (CDC, 2017).

Metrics and numeric limits

Not applicable.

Examples of drivers, outcomes and risk management

Cryptosporidium lives in the intestine of infected humans or animals. An infected person or animal sheds Cryptosporidium parasites in the stool. Millions of Cryptosporidium 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., diarrhoea) disappear. People become infected after accidentally swallowing the parasite (CDC, 2015).

The reported incidence of Cryptosporidium ranges from <1% in high income countries up to 8% in low- and middle-income countries. In 2016, Cryptosporidium infection was the fifth leading diarrhoeal aetiology in children younger than 5 years, and acute infection caused more than 48,000 deaths and more than 4.2 million disability-adjusted life-years lost (Khalil et al., 2018).

Cryptosporidium may be found in soil, food, water, or surfaces that have been contaminated with faeces from infected humans or animals. Cryptosporidium is not spread by contact with blood. It can be spread by: ingesting something that has come into contact with the stool of a person or animal infected with Cryptosporidium; swallowing recreational water contaminated with Cryptosporidium (e.g., contaminated with sewage or faeces from humans or animals); swallowing unfiltered water or beverages contaminated by stools from infected humans or animals; and eating uncooked food contaminated with Cryptosporidium. All fruit and vegetables eaten raw should be thoroughly washed with uncontaminated water. Hands can become contaminated through a variety of activities, such as: touching surfaces (e.g., toys, bathroom fixtures, changing tables, nappies) that have been contaminated by stools from an infected person; caring for an infected person; and handling an infected animal such as a cow or calf (CDC, 2015).

People with greater exposure to contaminated materials are more at risk for infection. These groups include: children who attend childcare centres, including pre-toilet trained children; childcare workers; parents of infected children; older adults (ages 75 years and over); people who care for other people with cryptosporidiosis; international travellers; 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; and people exposed to human faeces through sexual contact (CDC, 2015).

Several community-wide outbreaks of cryptosporidiosis have been linked to drinking municipal water or recreational water contaminated with Cryptosporidium. Travellers’ to developing countries may be at greater risk for infection because of poorer water treatment and food sanitation, but cryptosporidiosis occurs worldwide (CDC, 2017).