Story at-a-glance -

• The CDC reports cryptosporidium, triggering diarrhea, fever and fatigue, is the third leading cause of diarrheal illness in the U.S.; of the 444 outbreaks reported between 2009 and 2017, 35% were linked to treated swimming pools
• Although uncomfortable and distressing, it is not a serious infection in those with a strong immune system, but it may be life-threatening in those who are immunocompromised by inherited diseases, medications or illness
• Symptoms are caused by the parasite burrowing into the epithelial lining of the intestinal tract, where they reproduce, developing thin-walled spores that reinfect the host, or thick-walled spores that are excreted in the stool in search of a new host
• Take precautions before entering the swimming pool. Check for safety testing in public pools, consider using your own test strips, take a shower before entering the pool and do not drink pool water

During the summer months many take to the local swimming pools to cool off and enjoy time with family and friends. Families may spend time teaching their youngsters the life-saving skill of swimming1 or just hours splashing around and playing games in the water. However you spend your time in or near water, you don’t have to leave with more than you arrived with.

Unfortunately, public swimming pools and hot tubs may be hotbeds of unwanted activity. The Children's Hospital of Philadelphia warns children may acquire impetigo, pseudomonas dermatitis and athlete’s foot from swimming in pools.2 The EHA Consulting Group adds exposure to Escherichia coli, cryptosporidium (crypto) and shigella to the group.3

The parasites and bacteria in the list — Escherichia coli, cryptosporidium, and shigella — trigger infectious diarrhea,4 which may be fatal in those who are immunocompromised.5,6 In particular, the CDC warns cryptosporidium is the leading cause of diarrhea outbreaks linked to water and the third linked to animal contact.7

Cryptosporidium outbreaks rising — third leading cause of diarrhea

In June 2019 the CDC8 reported that cryptosporidium outbreaks increased, on average, 13% each year between 2009 and 2017. During this period, 444 cryptosporidiosis outbreaks were recorded, in which 7,465 cases were found in 40 states and Puerto Rico.

The CDC9 defines an outbreak as two or more infections linked to a common source by location and time. These reports of cryptosporidium are voluntarily made to the CDC through the National Outbreak Reporting System. The first outbreak recorded was in 2009 and was the first year for NORS reporting. Of the reported infections, 287 were hospitalized and one person died.10

The most frequently recorded outbreaks associated with recreational water infections were from pools and water playgrounds.11 Of the 444 outbreaks, 35% were linked to treated swimming water; 15% were linked to contact with cattle (in particular, nursing calves); 13% were linked to child care settings and 3% were associated with drinking unpasteurized milk or apple cider.12

As with any food product, it is possible for raw milk to harbor microorganisms. When cattle are raised in concentrated feeding operations the milk must be pasteurized to reduce the possibility of foodborne illness, although it does not eliminate it.13,14,15

A recent study revealed the rate of outbreak in raw milk has effectively decreased by 74% since 2005,16 while leafy greens account for 46% of all foodborne illnesses, according to CDC data.17

Your risk of exposure to cryptosporidium is introduced by swallowing the parasite from contaminated water or uncooked foods. You can also come in contact with it from touching surfaces like bathroom fixtures, changing tables and diaper pails and then touching your hand to your mouth.18

Although not normally serious in those who have strong immune systems, it may be life-threatening for those who are immunocompromised. Those at higher risk19 include people with HIV/AIDS, those with inherited diseases affecting the immune system or cancer and transplant patients taking medications which suppress the immune system.

The CDC warns20 exposure during the peak summer season from a treated recreational water source may result in hundreds or thousands of cases, since one infected swimmer may excrete up to 108 oocysts in one diarrheal incident. The oocysts survive seven days or longer, even in the presence of recommended concentrations of chlorine. Considering that swimmers may use multiple pools, the risk is multiplied even further.

How does cryptosporidiosis develop?

Cryptosporidium begins life as a sporulated oocyst that enters the environment through the stool of an infected host.21 The oocysts are resistant to chlorine treatment and may be found in drinking water supplies. They may also withstand freezing temperatures.

After a suitable host has ingested the spores and the spores enter the intestinal tract, the oocyst releases sporozoites, the motile asexual form of the parasite, which develops inside the oocyst.22 The sporozoites dig into the epithelial lining of the lungs (if the spores were inhaled) or the intestines when the spores were ingested. The cells then undergo asexual reproduction leading to a sexual reproductive stage.23

After fertilization, the resulting zygote develops into one of two types of oocysts. A thick-walled oocyst exits the host into the environment or a thin-walled oocyst will autoinfect the host.24 The infectious thick-walled oocysts are passed through the feces of the host and the cycle begins again.

What are the symptoms of cryptosporidiosis?

An infection with cryptosporidium may result in a variety of symptoms, the most characteristic of which is diarrhea.25 In an immunocompetent individual, the diarrhea is self-limiting and usually resolves within three weeks. The illness may be associated with fever or fatigue, and while the small intestine is chiefly affected, cryptosporidiosis has been found in the pulmonary and biliary tracts.26

Specifically, the diarrhea is watery and may become explosive.27 Explosive diarrhea is a severe form of the condition during which the individual passes liquid and gas when the rectum fills with more than it may hold.28

Normally, the large intestine is the last stop for waste products traveling through the gastrointestinal tract and is where excess fluid is absorbed. However, during a diarrheal process, the intestines move too quickly for the large intestine to absorb fluid.29

Use precautions at the pool

It is important to use precautions before going into a public or private swimming pool. Diarrheal illnesses in swimmers may be passed through pool water. Anyone who currently has diarrhea or who may have been sick with in the last two months will risk contaminating the pool with bacteria or parasites.30 Microscopic feces may contaminate an entire pool or hot tub, making other swimmers sick if they ingest the water.31

While many public and private pool owners seek to maintain a healthy pool environment, it's important to remember sporulated cryptosporidium are able to withstand the chlorine treatment. Giardia is another that may survive for up to 45 minutes in chlorinated pools.32

Precautions33 everyone should take before getting into the water include showering to remove as much dirt and bacteria before entering a pool. Importantly, don't pee or poop in the water and don't swallow the water. The CDC34 recommends taking children on bathroom breaks every hour, changing diapers away from the pool area and drinking plenty of fluids to stay hydrated.

The first line of defense is to keep those with any illness out of a swimming pool, public or private. While it is difficult to stop children from drinking pool water, it is considerably easier to prevent them from using toys like cups and buckets that might encourage them to put water in their mouth.

Test the water and report your symptoms

Another step you may take is to check inspection scores posted by the health department. This is similar to the way restaurants post scores of their sanitation practices. While many public pools are subject to testing, private pools usually are not. To test yourself, consider getting inexpensive test strips at big box stores.

In a survey conducted for the Water Quality and Health Council (WQHC), it was reported that 25% of adults said they would swim within one hour of having diarrhea, 50% never shower before going into a pool and 60% said they’ve swallowed pool water.35 The same survey reported that 72% of adults said they were unaware crypto was a parasite often spread by water.

In a press release from the CDC36 in 2016, the agency released inspection data collected in 2013 from five states with the most recreational water venues, including public pools and hot tubs. Data on 84,187 routine inspections found 1 in every 8 resulted in an immediate closure because of serious violations, while almost 80% identified at least one violation. The most common violations were improper pH, safety equipment issues and problems with disinfectant concentration.37

The CDC recommends38 that when visiting swimming pools you should complete your own inspection for some of the more common health and safety problems, including using test strips to determine chlorine and bromine concentrations. Make sure the drain at the bottom of the deep end is visible and check that the drain covers are secure and in good repair.

If a lifeguard is not on duty, make sure there is safety equipment nearby, such as a rescue ring.39 Since cryptosporidium may remain in the small intestine for as long as two months, during which you may pass the infection,40 if you’ve been sick with diarrhea, it is important to stay out of the pool and report your symptoms to the local or state health department, which reports to the CDC.41

Avoid hyperchlorination of your private pool or hot tub

Following an outbreak of cryptosporidium in Ohio,42 during which multiple cases were identified and linked to one swimming pool, researchers reported the offending pool was subsequently hyperchlorinated. A case-control study was launched to find the source of the outbreak; 150 confirmed and probable cases were identified and associated with the swimming pool.

Researchers found through this investigation that proactive measures may decrease transmission and prevent an outbreak. However, while hyperchlorination was used in this situation, there are dangerous compounds that form when chlorine is mixed with carbon-based compounds such as urine, poop and dirt.43

In one study,44 researchers mixed uric acid derived from human urine with chlorine and discovered it created two highly toxic detergent byproducts (DBPs): cyanogen chloride and trichloramine. Cyanogen chloride is classified as a chemical warfare agent with known pulmonary, heart and central nervous system toxicity.45 Trichloramine has been linked to lung damage in pool workers.46

The combination of chlorine and carbon compounds creates more than these two DBPs. In one study,47 researchers found spending just 40 minutes in a chlorinated pool was linked to DNA damage by these chemicals. The cancer risk of the DBPS is greater from skin exposure than from drinking water.48

Lack of cryptosporidium awareness may increase risk

Cryptosporidium has become one of the most common causes of waterborne disease.49 The parasite may be found throughout the U.S. and the world.50 Washing your hands thoroughly after using the bathroom or changing diapers becomes more urgent as you become aware that diseases are caused by a parasite that's basically spread through exposure to feces.51

The parasite spreads when you touch your mouth with contaminated hands. Your hands become contaminated after touching objects that were perhaps first touched by infected hands.52 Objects such as stair railings, elevator buttons, door knobs and baby toys are all fair game.

You're not always able to tell by looking if something has been in contact with fecal matter since only a minute amount is necessary to pass cryptosporidium spores. To reduce the spread of the parasite it’s important for you help to spread the word to friends and family and share why showering before entering the pool is one preventive step they may take.53

The parasite is notorious for being impervious to chlorine.54 In order to kill or inactivate it in drinking water, the water must be brought to a rolling boil for one minute. If you live at elevations above 6,500 feet, the water must be boiled for three minutes.55 The water should then be cooled and stored in a clean, sanitized glass container with a tight cover in the refrigerator.