1993 Milwaukee Cryptosporidiosis outbreak

On April 5, 1993, Milwaukee Health Department received increased reports of gastrointestinal (GI) illness at their local hospitals and calls of complaints related to reduced water-quality aesthetic. Water aesthetics include taste, color, odor, hardness/softness, and turbidity are considered a secondary standard under the EPA National Primary Drinking Water Regulations (NPDWR). Although these drinking aesthetics are under the EPA NPDWR, they are not federally enforced but standard regulations that states may choose to adopt and enforce themselves. Public health officials suspected recent illness to be due to water consumption. To verify suspicions, both the water treatment plants complied with data 30 days prior to the incident. The only findings were that turbidity was slightly increased but still below federally recommended levels. At the same time, hospitals did not routinely screen for cryptosporidium but because patients were all experiences similar symptoms hospitals were asked to test for cryptosporidium. Cryptosporidium is a chlorine resistant enteric pathogen that causes gastrointestinal illness such as diarrhea. Independent tests were run through the Milwaukee Public Health Laboratory (MHDL), to test stool samples for cryptosporidium. On April 7th, two days after initial reports, the Mayor of Milwaukee issued a ten-day advisory for residents to boil their drinking water. The process of boiling water is effective in killing potential pathogens however, this method cannot be used on a wide-scale as it is not as effective as water treatment plants and in some instances can be harmful. Furthermore, boiling water is only useful for drinking water. This means that people can still come into contact with harmful pathogens through their showers, washing machines, and sinks.

The root cause of epidemic was never officially identified; initially it was suspected to be caused by the cattle genotype due to runoff from pastures.[1] It was also thought that melting ice and snowmelt carrying Cryptosporidium may have entered the water treatment plants through Lake Michigan.[2] MacKenzie et al. and the CDC showed that this outbreak was caused by Cryptosporidium oocysts that passed through the filtration system of one of the city's water-treatment plants, arising from a sewage treatment plant's outlet 2 miles upstream in Lake Michigan. This abnormal condition at the water purification plant lasted from March 23 through April 8, after which, the plant was shut down. Over the span of approximately two weeks, 403,000[3] of an estimated 1.61 million residents in the Milwaukee area (of which 880,000 were served by the malfunctioning treatment plant) became ill with the stomach cramps, fever, diarrhea and dehydration caused by the pathogen.[3] Deaths have been attributed to this outbreak, mostly among the elderly and immunocompromised people, such as people with AIDS. [4]

The economic burden of this outbreak heavily impacted residents and workers in Milwaukee. To understand this impact, the CDC partnered with the Milwaukee and Madison health department to conduct a four-month cost analysis breakdown through the use of phone surveys, household estimates, and hospital cost estimates. To assess the finical burden to residents, they sorted patients based on the degree of medical attention received. Mild cases were described as not receiving medical care during illness, moderate was described as receiving medical care but not hospitals, and severe cases were those who were hospitalized. The results of their study found that for mild cases the average cost of illness per person was $116, moderate was an average of $475, and severe averaged $7,800. Fees included transportation, screening, laboratory tests, number of days stayed in the hospital, and productivity loss of an average worker.   

• Nationwide improvement of water-quality standards.
  • EPA Surface Water Drinking Rules were amended and EPA expanded research to focus on treatment of water related to pathogens.
• The City of Milwaukee started following the USEPA Interim Surface Water Drinking Rules after the outbreak.
• Hospital screening were adjusted to accurately represent cryptosporidiosis symptoms
  • Outpatient screening were revised for better patient follow-up.
• Local partnership with Milwaukee water treatment plants and health department to ensure communication and response to the public. The collaboration is called the Interagency Clean Water Advisory Council (IACWAC).
• Renovation of both north and south water treatment plant in 1994 to uphold new EPA and Wisconsin DNR standards.
• Approximately $415 million dollars were invested to improve the water infrastructure in the city.

• Cryptosporidium
• 1987 Carroll County Cryptosporidiosis outbreak
• Pryor Avenue Iron Well
• Water supply

5. Osewe, P., Addiss, D., Blair, K., Hightower, A., Kamb, M., & Davis, J. (1996). Cryptosporidiosis in Wisconsin: A case-control study of post-outbreak transmission. Epidemiology and Infection, 117(2), 297-304. doi:10.1017/S0950268800001473

6. Milwaukee, 1993: The Largest Documented Waterborne Disease Outbreak in US History. (2014, January 10). Water Quality and Health Council. https://waterandhealth.org/safe-drinking-water/drinking-water/milwaukee-1993-largest-documented-waterborne-disease- outbreak-history/

• CDC Cryptosporidium
• EPA Surface Water Drinking Rules
• Drinking Water Requirements for States and Public Water Systems
• Milwaukee Health Department Lab
• Cryptosporidium and public health (Drinking Water and Health Newsletter)
• Cost of Illness in the 1993 Waterborne Cryptosporidium Outbreak, Milwaukee, Wisconsin (CDC)
• A Massive Outbreak in Milwaukee of Cryptosporidium Infection Transmitted through the Public Water Supply