These Germs Can Survive in Pool Chlorine

Chlorine packs a punch, but these germs fight back.

Chlorine. We swim in it. We wash ourselves with it. We drink it. We trust chlorine to disinfect our water from the viruses, bacteria, amoebas and other microscopic miscreants that mean to do us harm.

But chlorine can't kill everything. Last week, more than 100 people across three counties in Ohio fell ill to cryptosporidiosis, an illness resulting from a parasite they likely came into contact with while swimming. The parasite responsible can survive up to 10 days in chlorine-treated waters thanks to its tough exterior.

So where exactly does this parasite come from? (Note: If you value your swim time, complete with inflatable lounge chair, floaties and pool noodle, don't read any further. You're better off just watching the video below.)

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Cryptosporidiosis is a diarrheal illness that can be contagious for up to two weeks after symptoms disappear. Infected swimmers dive in, and others in the pool at some point inadvertently swallow contaminated water, becoming infected themselves. Gross.

Here's where it gets worse: The crypto parasite isn't alone. There are other pathogens that can survive in chlorine just long enough potentially to ruin your summer.


Giardia (also known as Giardia intestinalis, Giardia lamblia, or Giardia duodenalis) is a parasite that causes the aptly named giardiasis, a diarrheal illness that can live one to two weeks or longer, according to the Centers for Disease Control and Prevention(CDC).

Like the crypto parasite, Giardia has a tough outer shell that allows it to survive chlorine disinfection, though only for about 45 minutes.

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Norovirus, the stomach scourge that comes on quick and strong, occasionally threatens visitors to water parks, cruise ships and even political conventions. It is a viral diarrheal illness (yes, again) typically associated with ingesting contaminated food.

Chlorine can kill the virus, but it takes between 30 and 60 minutes to work, a challenge at water attractions that draw large crowds. As with cryptosporidiosis, the unlucky infected can be contagious up to three weeks after recovery.

Toxoplasma gondii

Toxoplasma gondii isn't just for cats anymore (and hasn't been for some time). The protozoan parasite can cause human toxoplasmosis, a potentially life-threatening condition in individuals with compromised immune systems.

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Most people infected with the parasite don't realize they have it, according to the CDC, and may experience flu-like symptoms such as swollen glands or muscle aches, which can last over a month. At its worst, toxoplasmosis can cause damage to organs, including the eyes and brain.

Often, a Toxoplasma infection stems from eating or improperly handling undercooked, contaminated meat. It can also be found in feline feces, for those who have a contaminated cat at home. The parasite also can contaminate drinking water and is highly resistant to chlorine disinfection.


Sixteen minutes. That's how long it takes for chlorine to kill the virus that causes hepatitis A.

Hepatitis A is a diarrheal illness -- you know the drill. Sick person swims; healthy person swims; healthy person gets sick. And the cycle continues.

In adults, hepatitis A is typically no longer contagious after two weeks. But in children and individuals with weak immune systems, it can take as long as six months for them to no longer be capable of spreading the disease.

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Legionella likes it hot. The bacteria is typically found in hot tubs, hot water tanks and heaters, as well as cooling towers and decorative fountains, according to the CDC.

At higher temperatures, Legionella grows at a faster rate, and more chlorine is needed to kill off the microbes.

The bacteria can cause those infected to develop either Legionnaire's disease, which has symptoms similar to pneumonia that can crop up as late as two weeks after exposure, or Pontiac fever, a milder disease that can cause fever and muscle aches for about a week.

Staying Safe

For anyone looking to avoid sharing more than just the water with any of their fellow swimmers, there are a few tips to stay safe this summer:

1) Don't swallow pool water. At this point, you should know where many of the pathogens that could be contaminating the pool water came from. Don't drink it.

2) Shower with soap and water before and after swimming. Who knows what you might be bringing into the pool, or what other swimmers dove in with?

3) If you're sick, stay out of the water. If you've recently been sick, stay out of the water. If you think you might be getting sick, stay out of the water.

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