Pools and hot tubs have always been known to be epicenters of infection. Despite the many attempts to kill bacteria and other assorted germs with chemicals like chlorine, certain unsanitary practices (like peeing in the pool, for instance) may undermine treatment methods and spread disease. But does that mean we should refrain from swimming altogether?

According to a recent report from the Centers for Disease Control and Prevention (CDC), cases of contamination within pools, hot tubs, and lakes have been on the rise in the past few years. The culprit: a parasite called Cryptosporidium, which can reside in treated water without being harmed.

This is not the first CDC report of this nature; another statement issued in 2013 found that a majority of both indoor and outdoor pools contained fecal matter. This new form of contamination, however, is particularly dangerous as it can survive up to 10 days in a chlorinated environment. The CDC found that 90 documented outbreaks associated with Cryptosporidium have been reported in 32 states and Puerto Rico between the years 2011 and 2012. These illnesses infected about 1,788 people, resulting in 95 hospitalizations and one death. All of these cases were found to come from recreational water, like pools, hot tubs, and lakes.

“Since 1988, the year that the first U.S. treated recreational water-associated outbreak of Cryptosporidium was detected, the number of these outbreaks reported annually has significantly increased,” the report says.

According to Mayo Clinic, when the parasite enters your body, it burrows within your small intestine, usually bringing on bouts of diarrhea. The parasite will go away within a week or two through fecal matter, but in rare cases, death can result if the person has a compromised immune system. It is advised to avoid swallowing water, so that the parasite is not consumed.

“This parasite is extremely chlorine-resistant,” Michele Hlavsa, lead author of the report, told CBS News. “Swimmers bring it into the water when they are sick with diarrhea.”

CBS News’ medical contributor, Dr. Holly Phillips, found this outbreak to be particularly alarming because it is happening in public water that has been chemically treated as a precaution. “One of the most striking things about this report is that 77 percent of these outbreaks are happening in treated water,” she said.

Hlavsa believes the way to prevent these outbreaks is to regulate and maintain one set of health standards for all recreational water. “There are different standards and people are responding differently,” she said. “We need a certain set of standards and it should be the same across the country.”

CBS also states that in 2014, the CDC issued specific guidelines on how to keep water clean and prevent contamination. This report, known as the Model Aquatic Health Code (MAHC), recommended installing secondary forms of decontamination within recreational waters, like ultraviolet light or ozone, to kill Cryptosporidium.

The report also noted an increase in outbreaks within untreated waters as well, finding bacteria like E. coli within oceans and lakes throughout the country. Between 2011-2012, these outbreaks have been responsible for cases of diarrhea, nausea and vomiting among those infected.

“It comes from the swimmers themselves or it could be that the lakes and oceans are impacted by what’s washing off into them,” Hlavsa said.

The CDC concluded its report by saying the best way to keep water clean and stop the spread of disease is to avoid swimming if you recently had diarrhea, refrain from swallowing water, shower before you get into water, and, most importantly, do not use public water as your toilet.  

Source: Hlavsa M, Roberts V, Kahler A, et al. Outbreaks of Illness Associated with Recreational Water — United States, 2011–2012. Morbidity and Mortality Weekly Report. 2015.