Cryptosporidium: What It Is, How It Spreads, and How to Stay Safe

When you think of waterborne illness, you might picture old-school cholera or typhoid. But Cryptosporidium, a microscopic parasite that lives in the intestines of humans and animals and is shed in feces. Also known as Crypto, it’s one of the most common causes of water-related sickness in the U.S. and Europe, and it’s not going away. Unlike bacteria, it doesn’t die easily. Chlorine in swimming pools won’t kill it. Boiling water for a full minute is one of the few things that actually works.

Cryptosporidium doesn’t just show up in lakes or public pools. It’s in untreated well water, in daycare centers where kids don’t wash hands well, and even in food washed with contaminated water. People with weak immune systems—like those on chemo, with HIV, or after organ transplants—can get seriously ill from it. But even healthy adults can end up with days of watery diarrhea, stomach cramps, nausea, and fever. It’s not just a bug you get on vacation. It’s in your local water supply if it’s not filtered properly.

Related parasites like Giardia, another intestinal parasite spread through contaminated water and fecal matter often get confused with Crypto. But they’re different bugs with different treatments. While Giardia responds to certain antibiotics, Crypto has no reliable drug cure. That’s why prevention is everything. If you’re traveling, if you have young kids, or if you rely on a private well, you need to know how to spot the risks. Filters labeled NSF 53 or NSF 58 can remove Crypto. Bottled water is safer than tap in high-risk areas. Handwashing with soap after using the bathroom or changing diapers cuts transmission by half.

There’s no vaccine. No magic pill. And no way to ignore it if you care about your health or your family’s. The posts below cover real cases, how it shows up in medical settings, what doctors actually recommend when symptoms hit, and how to avoid it in daily life—from swimming pools to petting zoos. You won’t find fluff here. Just clear, practical advice from people who’ve dealt with it firsthand, and the experts who’ve studied it for years.