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(CNN) —  

Health officials are asking Americans to take precautions over reports that “crypto,” a fecal parasite that can be transmitted via swimming pools, is on the rise.

The parasite’s full name is cryptosporidium. It causes cryptosporidiosis, which can leave healthy adults suffering from “profuse, watery diarrhea” for as long as three weeks. The effects can be worse for children, pregnant women and those with compromised immune systems.

“The number of treated recreational water-associated outbreaks caused by cryptosporidium drives the summer seasonal peak in both waterborne cryptosporidiosis outbreaks and cryptosporidiosis outbreaks overall,” according to a statement from the US Centers for Disease Control and Prevention.

Though it’s almost never fatal, one death has been reported since 2009, according to the CDC. Another 287 people were hospitalized between 2009 and 2017, the CDC says.

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A CDC report released Friday explains why health officials are alarmed:

The CDC adds two caveats to the figures, which it suspects underestimate the number of actual cases and outbreaks: The spike in cases may be the result of new testing technology, and the requirements and ability to detect, investigate and report cases vary across jurisdictions.

  • Between 2009 and 2017, there were 444 cryptosporidiosis outbreaks reported in 40 states and Puerto Rico.
  • The outbreaks resulted in 7,465 people falling ill.
  • Recreational water – mostly swimming pools, but also kiddie pools and water playgrounds – were responsible for 156, more than a third of the cases.
  • Untreated water (such as lakes) and drinking water caused 22 more cases.
  • Eighty-six cases involved contact with animals, mostly cattle.
  • Another 57 cases were associated with child care settings.
  • Twenty-two cases were foodborne, most involving unpasteurized milk or apple cider.
  • Most cases were reported in the months of July and August, and 2016 was a peak year for outbreaks with more than 80.
  • The number of cases increased by an average of 12.8% annually between 2009 and 2017.

It’s also worth noting the one death from cryptosporidiosis came in the sole instance in which the parasite was transmitted in a hospital setting.

In pools, cryptosporidium can enter the body when a swimmer swallows contaminated water.

The parasite is a problem in pools is because an infected swimmer can excrete the parasite at several orders of magnitude higher than the amount necessary to cause infection. Cryptosporidium has a high tolerance to chlorine and can survive in a properly chlorinated pool for up to seven days, the CDC says.

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There are preventative measures that can help stem the number of outbreaks, and the CDC is working to educate the public on them.

Youngsters sick with diarrhea should not be placed in child care, according to the CDC, and following a cryptosporidiosis outbreak, child care workers should clean surfaces with hydrogen peroxide, as chlorine bleach is an ineffective means of killing the parasite.

People who come in contact with livestock should wash their hands thoroughly and remove any shoes or clothing to avoid contaminating other environments, like their homes.

As for pools, anyone suffering diarrhea should avoid swimming until at least two weeks after their diarrhea subsides, the CDC says.

That last one is most important, as 24% of American say they’d jump in a swimming pool within an hour of having diarrhea, according to a survey released last month by the Water Quality & Health Council.