More than 100 individuals in Maricopa County in Arizona have been infected with a parasite that officials believe thrive in at least 20 pools in the community.

Health officials are already working to stop the outbreak at several swimming pools to respond to public concerns since the parasite, known as cryptosporidium, or "crypto," was first reported earlier this month.

The parasite, which has caused illness in more than 100 people at about 20 recreational water facilities, can cause diarrhea, stomach cramps, vomiting and fever. Those with healthy immune systems usually recover after a week or two even without treatment but those with weakened immune system may develop chronic, serious and sometimes deadly illnesses.

People at risk for serious symptoms are those with inherited diseases affecting the immune system, patients with AIDS or cancer and transplant patients who take certain immunosuppressive drugs.

Although the small intestine is often the site affected, cryptosporidium infection in immunocompromised persons may affect areas of the respiratory or digestive tracts.

"Once infected, people with decreased immunity are most at risk for severe disease. The risk of developing severe disease may differ depending on each person's degree of immune suppression," the Centers for Disease Control and Prevention (CDC) said.

Health authorities did not identify contaminated pools but urged potentially contaminated facilities to be treated. The public is likewise encouraged to be cautious when using public pools, properly wash hands with soap and water as well as frequently take bathroom breaks out of the pool to prevent spreading the highly contagious disease.

The disease spreads in pools when infected people contaminate the water with fecal matter. Pools cannot be tested for the parasite but officials identify potentially contaminated swimming facilities after somebody who swam there reported becoming sick.

"The most important thing the public can do to prevent spread of this disease is to stay out of the water if you have diarrhea, until at least two weeks after symptoms resolve," said Dr. Rebecca Sunenshine, Maricopa County Department of Public Health medical director.

The parasite is difficult to get rid of because it has strong immunity against chlorine. Chlorine is popularly used to kill other pathogens in the water. People can contract the parasite when they drink contaminated water or beverages or when they swallow recreational water contaminated by the parasite.

Authorities discovered the parasite in Maricopa County on Aug. 4 after 19 people fell ill in July.

Earlier this month, health officials in Ohio declared a crypto outbreak following an increase in cases of the diarrheal illness.