A parasite outbreak is plaguing swimming pools in Phoenix, Arizona.

Cryptosporidium or Crypto, a microscopic parasite that causes diarrhea, has contaminated 20 public recreational water facilities in Maricopa County and affected over 100 people. Officials of the Maricopa County Department of Public Health (MCDPH) and the Environmental Services Department (MCESD) are responding to growing health concerns.

"[We recommend] that any facility in which an infected person swam prior to illness or while sick be treated for Crypto," health authorities said in a report by CNN. "MCESD is notifying the facilities that are affected and recommending that CDC guidelines for decontamination are being followed."

The parasite spreads in swimming pools through contact with infected feces. Crypto could enter people's bodies through their mouths or open wounds, and it is also capable of surviving for about 10 days even in chlorinated water.

As of the moment, health authorities have no way of testing the pools for the presence of parasites. Health officials could only identify a contaminated pool after a person who swam in the pool reports becoming ill, CNN reports.

"Right now, this outbreak is community-wide and there is an increased risk to those swimming at recreational water facilities," Rebecca Sunenshine, medical director for MCDPH, said in a statement.

"The most important thing the public can do to prevent the spread of this disease is to stay out of the water if you have diarrhea, until at least two weeks after symptoms resolve."

Pool swimmers are encouraged to take restroom breaks when out of the water, wash their hands thoroughly with soap and avoid swallowing pool water.

According to a recent CDC report, cryptosporidium had caused 37 out of 69 outbreaks of illnesses in swimming pools and recreational water facilities in 2011 to 2012.

Affected people will experience diarrhea for about 2 to 10 days after the infection, but some people may not have any symptoms at all.