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This article waslast modified on November 19, 2019.

Outbreaks of the diarrhea-causing parasite Cryptosporidium (commonly called Crypto) in swimming pools and other water features are on the rise, warns the Centers for Disease Control and Prevention (CDC) in a report published June 28. Between 2009 and 2017, nearly 450 outbreaks were reported, which resulted in 7,465 illness, 287 hospitalizations, and one death.

The CDC's Morbidity and Mortality Weekly Report showed 13% average annual increase in outbreaks of Cryptosporidium, which is the leading cause of water-related disease outbreaks, specifically those at pools or water parks. Out of the 444 outbreaks reported between 2009 and 2017, 35% were linked to swimming water, while 15% were linked to contact with cattle, 13% to contact with infected people in childcare settings, and 3% to drinking unpasteurized milk or apple cider.

Although the chlorine in swimming pools typically kills pathogens, Cryptosporidium is resistant to the chemical due to its protective outer shell. To avoid spreading the disease, people with diarrhea shouldn't go in the pool or other water play areas. People with a diagnosed Cryptosporidium infection should avoid entering the swimming pool for at least 2 weeks. Everyone should avoid swallowing pool water, the most common way to acquire the infection.

Other prevention tips include washing your hands thoroughly with soap and water after using the toilet, changing diapers, or touching animals. (Alcohol-based hand sanitizers are not effective against Cryptosporidium.) Avoid drinking unpasteurized milk or apple cider. Additionally, children with diarrhea should be kept home from childcare facilities. Children are particularly prone to acquiring and spreading the infection because they are just learning how to properly use the toilet, wash their hands, and swim safely without swallowing water.

The illness that results from a Cryptosporidium infection is called cryptosporidiosis. Typical signs and symptoms include nausea, vomiting, cramping and profuse, watery diarrhea that starts between 2 and 10 days after getting infected and usually lingers for one to two weeks. Other symptoms include fever, stomach pain, weight loss, and dehydration.

In most cases, cryptosporidios is self-limiting. It usually resolves on its own without specific medical treatment and only supportive care may be necessary (e.g., drinking plenty of fluids to avoid dehydration and sometimes modifying the diet). However, young children, the elderly, people with weakened immune systems and pregnant women can experience longer-lasting infections and symptoms as well as complications. If the symptoms of a parasite infection aren't clearing up on their own or a person is experiencing complications such as dehydration or an electrolyte imbalance, a healthcare practitioner may order testing to identify the pathogen causing the infection. Testing may also be done by public health laboratories as part of an investigation of an outbreak.

A diagnosis may be made by using a microscope to examine a sample of stool that has been placed on a slide and stained. Usually, more than one stool sample is collected on different days and tested to increase the chance of detecting the parasite. Other laboratory tests used to detect the parasite in stool include immunoassays or methods that detect the genetic material of the parasite (e.g., gastrointestinal pathogens panel), which may be used in select cases.

Treatment options are limited. Anti-diarrhea medications may be used to help slow down diarrhea and increase fluid absorption, but these should be used only on the advice of a healthcare practitioner. In people who are severely ill, fluids may be given through a vein (intravenous) to keep them hydrated and their electrolytes such as sodium, potassium and calcium in balance.

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June 28, 2019. Cryptosporidiosis Outbreaks — United States, 2009-2017. Centers for Disease Control and Prevention. Available online at https://www.cdc.gov/mmwr/volumes/68/wr/mm6825a3.htm?s_cid=mm6825a3_w%5C. Accessed on July 20, 2019.

June 27, 2019. CDC Press Release: Outbreaks of Diarrhea Caused by Summertime Parasite Increased from 2009 Through 2017. Centers for Disease Control and Prevention. Available online at https://www.cdc.gov/media/releases/2019/p0627-outbreaks-diarrhea-summertime.html. Accessed on July 20, 2019.

July 1, 2019. Parasites – Cryptosporidium (Also Known as "Crypto"). Centers for Disease Control and Prevention. Available online at https://www.cdc.gov/parasites/crypto/index.html. Accessed on July 20, 2019.

November 30, 2016. Cryptosporidium Infection. Mayo Clinic. Available online at https://www.mayoclinic.org/diseases-conditions/cryptosporidium/symptoms-causes/syc-20351870. Accessed on July 21, 2019.

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Cryptosporidiosis. Johns Hopkins Medicine. Available online at https://www.hopkinsmedicine.org/health/conditions-and-diseases/cryptosporidiosis. Accessed on July 21, 2019.