Recent History: Cryptosporidosis!

It’s still summer, so let’s take a quick look at the history of a disease that (these days, in the United States), is most commonly acquired from pools and lakes while swimming. It can cause miserable stomach cramps, diarrhea, vomiting, and can be extremely dangerous to those with compromised immune systems. And not too long ago, it caused some major problems for almost a quarter of the largest city in Wisconsin…

1993. Milwaukee, WI. 

Anyone live on Milwaukee’s south side in March 1993? Personally, I was staying with my cousin over spring break, who lived in the area. As luck would have it, her house was served by the Howard Avenue Water Purification Plant…a plant that would soon make history. Of 880,000 people served by that treatment plant, 403,000 fell sick within a span of just over two weeks. Cramps, fever, vomiting, and diarrhea plagued so many people that some south side businesses were completely shut down due to lack of employees! Over $64 million (the most conservative estimate) was lost in productivity in a relatively small area in under a month.

Though “only” 104 people died in the end, people never expected something like this happening in the “modern” era. It was a massive blow to public confidence in their drinking water being safe, and in their municipal services in general.
However, thanks to this massive outbreak, water treatment plants and wastewater management all over the country are now far safer, have much better monitoring, sanitation, and filtration systems, and mini-outbreaks (that were not originally attributed to the same factors) have been nearly eliminated.


History Break! - 

1894. Milwaukee, WI:

Photograph: Milwaukee Public Health Laboratory

The huge cryptosporidosis outbreak was definitely not Milwaukee’s first run-in with water-borne illness. The Public Health department in Milwaukee began daily testing of water qualities back in 1894, and realized that the relatively high typhoid fever (which were not outbreaks, but constant) rates in the city were due to the dumping of almost 54 million gallons of raw sewage into Lake Michigan every day. 

Similar typhoid fever quarantine signs were used across the country, including in Milwaukee.

Even though tenements were being cleaned up and there wasn’t sewage in the streets for the most part, the raw sewage getting into the ground water led to almost as much typhoid as ever. They argued for the installation of water treatment plants, and the typhoid rates fell to record lows within less than a year after their construction. In fact, before the typhoid fever inoculation was available, Milwaukee maintained one of the lowest outbreak/death rates from the disease in any large city.

Jones Island Wastewater Treatment Plant being constructed - 1917.

The Public Health Laboratory in Milwaukee may have had to deal with multiple deadly epidemics and outbreaks, but from them, they’ve made impressive advances. After the typhoid reduction, the analysis techniques and statistical analysis used in placement of the treatment plants led to their specialists consulting with several other cities to reduce their own typhoid problems. Since the Cryptosporidium outbreak, the laboratory has been recognized as an international leader in detection and diagnostics of Giardia and Crypto.



Back to Crypto, and 1993! Cryptosporidium spp. was recognized as a group of enteritis-causing coccidians way back in 1907, when people were first beginning to differentiate diarrheal illnesses, instead of simply designating them “dysentery” or “typhoid”. However, it was not thought to be of much importance and largely ignored until 1976. In that year, it was differentiated from the other coccidians in its family, and was recognized as a major cause of diarrheal water-borne illness worldwide.

Cryptosporidium oocysts found in human stool sample

Today, we know that Cryptosporidium is:

  • A parasite; coccidum are single-celled eukaryotes, making them parasitic instead of bacteria or viruses.
  • Transmitted by water and feces, and outbreaks are largely because of contaminated water
  • Extremely widespread; almost 50% of diarrheal outbreaks in the world are due to some Crypto species.
  • Able to live a complete lifecycle in one host, unlike most parasites (for example, the parasites that cause malaria require both a human and a mosquito)
  • Able to infect humans thanks to the thick outer shell around the oocytes that doesn’t get destroyed by stomach acid. It gets softened, though, and the Crypto emerges to infest the small intestine.
  • Very dangerous to people with AIDS or other immuno-compromising conditions - in almost 35% of cases, Crypto causes chronic diarrhea, which weakens the body against opportunistic infections.
  • Easily killed by ozone at water treatment plants! Even though the water was treated in Milwaukee, chlorine obviously didn’t destroy the oocysts. Later tests showed that oocysts could be destroyed by ozone without a problem. These days, it’s is commonly used as an additional, safe, and inexpensive step to eliminate pathogens from treated water.

Cryptosporidium can be avoided by thoroughly cooking food, avoiding contact with human and animal feces and always washing raw foods thoroughly. One of the most important things to do to avoid Crypto is avoiding swallowing water while swimming in lakes, ponds, pools, and rivers. Since it’s chlorine-resistant, it survives even in treated pools. 

Even though Crypto is present in up to 90% of surface waters, treated water in most cities is free of oocysts, thanks to the use of microfilters smaller than 1 micron and (more commonly) the use of ozone as a disinfectant. 


CDC - Cost of Illness in the 1993 Waterborne Cryptosporidium Outbreak in Milwaukee, WI

NEJM - A Massive Outbreak of Cryptosporidium Infection Transmitted Through Public Water Supply

PubMed Health - Cryptosporidium Enteritis

CDC Fact Pages - Parasites: Cryptosporidium (also known as “Crypto”)

City of Milwaukee Health Laboratory History

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