What's in Your Water?

Early 1993, Milwaukee, Wisconsin had the largest waterborne-disease outbreak (WBDO) ever documented in the United States.

During this time frame two outbreaks of cryptosporidiosis occurred in large metropolitan areas, Milwaukee and Las Vegas/Clark County, and were associated with deaths among immunocompromised persons. The waterborne nature of these two outbreaks was not recognized until at least 2 weeks after the onset of the Milwaukee outbreak and until after the end of the Las Vegas outbreak. [1]

In Milwaukee, cattle were suspected to be the cause of the WBDO. It was theorized that melting snow from a local farm carried cow feces into the water supply. For approximately 10-years there was no definitive answer for the outbreak.

As the investigation continued and technology progressed, DNA would ultimately determine the cause. Stool samples collected from the afflicted back in 1993 was still stored by the Health Department and a molecular fingerprint was finally identified. The cause of the Cryptosporidium outbreak was determined by the strain, which was Cryptosporidium hominis. Cattle does not contain such a finger print, only humans do.[2]

Therefore, the WBDO was caused by human contaminant to human ingestion.

In late March 1993, a sewage leak is suspected to have released a parasitic cloud of Cryptosporidium infected human feces into the south side water supply. The cloud would have caused the spike in turbidity that was reported at the Howard Avenue Purification Plant. It was also the south side of Milwaukee that had the highest concentration of sickened individuals. [2]

One of Milwaukee's two water treatment plants was contaminated. Over the span of approximately two weeks, 403,000 of an estimated 1.61 million Milwaukee residents were sickened and approximately 100 persons killed. Some reports indicate that a majority of those deaths were among people afflicted with AIDS. [3]

By April of '93 the infected mass would have passed through the water supply resulting in a proper turbidity reading, but the damage was done. The ensuing WBDO wreaked havoc among the Milwaukee population striking the immunocompromised the worst. [2]

Turbidity is the cloudiness or haziness of a fluid caused by individual particles (suspended solids) that are generally invisible to the naked eye. The measurement of turbidity is a key test of water quality. In drinking water, the higher the turbidity level, the higher the risk that people may develop gastrointestinal diseases.

This is especially problematic for immune-compromised people, because contaminants like viruses or bacteria can become attached to the suspended solid. The suspended solids interfere with water disinfection with chlorine because the particles act as shields for the virus and bacteria. Similarly, suspended solids can protect bacteria from ultraviolet (UV) sterilization of water. [4]

Milwaukee took steps to ensure a similar outbreak would not happen again. Chlorine has no effect on Cryptosporidium so Milwaukee introduced ozone, the only agent capable of destroying Cryptosporidium. Milwaukee now has an ozone filtration system in place creating one of the cleanest water supplies in the US.

Ozone is effective but does not eliminate all of the parasitic presence. On average there are 10 Cryptosporidium parasites in every 10 gallons of NY drinking water, which at that concentration [usually] does not cause any illnesses. [2]

So, what's in your drinking water?

Resources:

1. Surveillance for Waterborne-Disease Outbreaks -- United States, 1993-1994

2. Animal Planet/Monsters Inside Me

3. 1993 Cryptosporidium Outbreak

4. Turbidity - Wikipedia, the free encyclopedia