HARRISBURG, Pa. (WHTM) – Summer time means pool time.

“Swimming is so healthy,” said Susan Kopp, an avid swimmer.

Your health is why the Centers for Disease Control and Prevention is warning of a rise in a summertime parasite called cryptosporidium, or crypto, that causes diarrhea.

It is spread through the waste of infected humans or animals, mostly in swimming pools.

“It’s resistant to chlorine,” said Dr. John Goldman, an infectious disease specialist at UPMC Pinnacle.

The CDC says between 2009 and 2017, there were 444 outbreaks in 40 states and Puerto Rico, an increase of about 13% per year.

“It’s one of these things that tends to be a self-fulfilling rise. If more people are sick, more people get into swimming pools. Other than that, it may be reported more than it used to be,” said Dr. Goldman.

So how do you know if you have it?

“Most bacterial diarrheal illnesses last two, three, maybe four days and cryptosporidium can last for a week or two weeks,” said Dr. Goldman.

The best way to prevent against contracting “crypto” is to not swallow any water in pools and shower immediately afterward.

“You have to count on other people to keep their sick kids, their sick selves, out of the swimming pool,” Goldman said.

Although crypto is almost never fatal, one death has been reported since 2009. The effects can be worse for children, pregnant women, and those with weakened immune systems. Most of the time, it resolves on its own.

“You can take antibiotics that may shorten the duration,” Goldman said.

For an avid swimmer like Kopp, being aware and hygienic are key.

“The warning will not impact my swimming time,” she said.