1993 Milwaukee cryptosporidiosis outbreak

Epidemiology

Cryptosporidium are a chlorine-resistant enteric pathogens that cause gastrointestinal illness (cryptosporidiosis) with symptoms such as diarrhea. Other symptoms include stomach cramps, dehydration, nausea, vomiting, fever, or weight loss. Symptoms can be more severe for people who are immunocompromised, for whom diarrhea can lead to death. Enteric pathogens are microorganisms that humans ingest, typically through contaminated food or water. Since Cryptosporidium is a coccidian parasite, it has oocysts. An oocyst is a period in the life cycle of a coccidian parasite. The oocysts in Cryptosporidium are the transmissible stage for cryptosporidiosis.

Most reports do not specify the species of Cryptosporidium involved in the outbreak. Several species cause cryptosporidiosis in humans, with most caused by Cryptosporidium parvum and Cryptosporidium hominis. However adding to the confusion, these two species were only split from each other in 2002. In 2003, Phaedra S. Corso et al. imply without evidence that it was C. parvum. but the 1994 source they cite does not specify the species. McDonald et al. do find positive results testing blood samples with antigens derived from C. parvum, but a 2018 paper from Sumeeta Khurana and Preeti Chaudhary indicate that antigen tests are not species-specific and that molecular methods are needed to differentiate other species. A 2003 study by Ling Zhou et al. specifically addresses these issues and clearly identifies the pathogen in this outbreak as C. hominis.

History

On April 4, 1993, pharmacist Jeff Langer contacted a local television station after the Milwaukee Health Department did not respond to his calls regarding substantial increase in gastrointestinal complaints. Sunday evening, April 4, the station came out to interview Jeff Langer regarding the substantial increase in requests for anti-diarrhea medications. Following that television interview, April 5, 1993, Milwaukee Health Department received additional reports of gastrointestinal 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. They 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 are standard regulations that states may choose to adopt and enforce themselves. In the spring of 1993, turbidity was the main complaint. This was corroborated by Milwaukee Water Works records of Maximal Turbidity for both water treatment plants from March through April 1993.

Causes

The root cause of the epidemic was never officially identified; however, it was most likely the result of human error at the Howard Avenue Water Treatment Plant. Initially it was suspected to be caused by runoff from upstream cattle pastures. It was also thought that melting ice and snowmelt carrying Cryptosporidium may have entered the water treatment plants through Lake Michigan.

Mac Kenzie 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 two 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. The increased turbidity of the treated water was mitigated by the added flocculant polyaluminum chloride, but peaked again on April 5 after the plant changed to alum three days prior. Over the span of approximately two weeks, 403,000 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. After the outbreak, cryptosporidiosis antibody rates among Milwaukee children reached 80%, compared to only 10% prior to the outbreak. Deaths have been attributed to this outbreak, mostly among the elderly and immunocompromised people, such as people with AIDS.

Social impact

Reports of gastrointestinal illness began in April 1993; however, studies occurring after the outbreak confirmed that there were echoes of the epidemic beyond initial contamination as the population contracted the illness through secondary transmission. This resulted in negative public sentiment toward Milwaukee Water Works. Carrie Lewis, superintendent of Milwaukee water works in 2015, explained that "people had been hurt, they felt let down by their drinking water and it took a long time for them to believe that we knew what we were doing again," It took ten years for Milwaukee citizens to begin to trust the public water supply again with the help of frequent community outreach by the utility.

Current treatment in Milwaukee

Currently, Milwaukee consistently scores as one of the highest drinking water qualities in the state. This is due to $508 million invested in water treatment and monitoring improvements since the outbreak. Improvements in treatment include:

• Activated charcoal filtration (Actiflo Carb) removes certain drugs, disinfectants, antibiotics
• Monitoring on each stream of flow (8 streams) – previously, streams were only monitored before and after branching off (no way to monitor individual streams)
• Collection pipe for water was moved further out in the lake to draw higher quality water
• Ozone treatment (treatment of chlorine-resistant microorganisms, such as Cryptosporidium)
• Online monitoring/automation

References

References

1. (April 2003). "Cost of illness in the 1993 waterborne Cryptosporidium outbreak, Milwaukee, Wisconsin". Emerging Infectious Diseases.
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3. Division of Foodborne, Waterborne, and Environmental Diseases (DFWED) Home. (2023). ''Enteric Diseases Epidemiology Branch.'' Washington, D.C.: Centers for Disease Control and Prevention.
4. Centers for Disease Control and Prevention. (2023). ''Cryptosporidiosis''. Retrieved from DPDx – Laboratory Identification of Parasites of Public Health Concern: https://www.cdc.gov/dpdx/cryptosporidiosis/index.html {{Webarchive. link. (2019-11-07)
5. Centers for Disease Control and Prevention. (2023). ''Parasites Glossary''. Retrieved from Parasites: https://www.cdc.gov/parasites/glossary.html#oocyst {{Webarchive. link. (2023-10-05)
6. (November–December 2002). "Cryptosporidium hominis n. sp. (Apicomplexa: Cryptosporidiidae) from Homo sapiens". Journal of Eukaryotic Microbiology.
7. (January–June 2018). "Laboratory diagnosis of cryptosporidiosis". Tropical Parasitology.
8. (1 November 2003). "Molecular Surveillance of Cryptosporidium spp. in Raw Wastewater in Milwaukee: Implications for Understanding Outbreak Occurrence and Transmission Dynamics". Journal of Clinical Microbiology.
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11. (December 1997). "Cryptosporidiosis-associated mortality following a massive waterborne outbreak in Milwaukee, Wisconsin". American Journal of Public Health.
12. (September 2007). "Cryptosporidium in Milwaukee's water supply caused widespread illness". Healio.
13. Lewis, C. (2015, January 9). Superintendent of Milwaukee Water Works. (M. Gonzalez, & B. Gonzalez, Interviewers)
14. City of Milwaukee. (2022). ''Water Quality''. Retrieved from Milwaukee Water Works: https://city.milwaukee.gov/water/WaterQuality {{Webarchive. link. (2023-12-04)
15. Ceraso, M. (2013). ''20 years after fatal outbreak, Milwaukee leads on water testing.'' Wisconsin Water Watch.
16. Milwaukee Public Water Works. (2023). ''FAQs – Water Quality and Public Health – Water Treatment Process''. Retrieved from City of Milwaukee: https://city.milwaukee.gov/water/customer/FAQs/qualityandhealth/Water-treatment-process.htm {{Webarchive. link. (2023-04-13)
17. (September 1999). "Ozone Disinfection; Wastewater Technology Fact Sheet". US Environmental Protection Agency (EPA).