(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 said.
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.
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.
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