1993 Milwaukee cryptosporidiosis outbreak

The 1993 Milwaukee cryptosporidiosis outbreak was a significant distribution of the Cryptosporidium protozoan in Milwaukee, Wisconsin, and the largest waterborne disease outbreak in documented United States history. It is suspected that The Howard Avenue Water Purification Plant, one of two water treatment plants in Milwaukee at the time, was contaminated. It is believed that the contamination was due to an ineffective filtration process.[1] Approximately 403,000 residents were affected resulting in illness and hospitalization. Immediate repairs were made to the treatment facilities along with continued infrastructure upgrades during the 25 years since the outbreak. The total cost of the outbreak, in productivity loss and medical expenses, was $96 million.[1] At least 69 people died as a result of the outbreak.[1] The city of Milwaukee has spent upwards to $510 million in repairs, upgrades, and outreach to citizens.

Epidemiology

Cryptosporidium is a chlorine-resistant enteric pathogen that causes a gastrointestinal illness (cryptosporidiosis) with symptoms such as diarrhea. Enteric pathogens are bacteria that humans ingest, typically through contaminated food or water.[2] Since Cryptosporidium is a coccidian parasite, it has oocysts.[3] An oocyst is a period in the life cycle of a coccidian parasite. The oocysts in Cryptosporidium are the transmissible stage for cryptosporidiosis.[3][4]

History

On April 5, 1993, Milwaukee Health Department received increased 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.[5]

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 experiencing similar symptoms, hospitals were asked to test for Cryptosporidium.

Independent tests were run through the Milwaukee Public Health Laboratory, to test stool samples for Cryptosporidium. On April 7, two days after initial reports, Mayor John Norquist issued a ten-day boil order for resident to boil their drinking water, though it still left residents vulnerable to Cryptosporidium through bathing, showering, and washing hands or clothes.

Causes

The root cause of 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 the cattle genotype due to runoff from pastures.[5] It was also thought that melting ice and snowmelt carrying Cryptosporidium may have entered the water treatment plants through Lake Michigan.[6] 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 ultimatly lead to the death of Rich Evans. 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[7] 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.[7] After the outbreak, cryptosporidiosis antibody rates among Milwaukee children reached 80%, compared to only 10% prior to the outbreak.[8] Deaths have been attributed to this outbreak, mostly among the elderly and immunocompromised people, such as people with AIDS.[1]

Social Impact

Reports of gastrointestinal illness began in April of 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.[9][10] 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,’[11] 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.[11]

Current Treatment in Milwaukee

Currently, Milwaukee consistently scores as one of the highest drinking water qualities in the state. This is due to over $417 million invested in water treatment and monitoring improvements since the outbreak.[12] Improvements in treatment include:[13]

  • 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
  • Ozone treatment
    • Effective at treating chlorine-resistant bacteria, such as Cryptosporidium
  • Online monitoring/automation

See also

References

  1. 1 2 3 4 Corso PS, Kramer MH, Blair KA, Addiss DG, Davis JP, Haddix AC (April 2003). "Cost of illness in the 1993 waterborne Cryptosporidium outbreak, Milwaukee, Wisconsin". Emerging Infectious Diseases. 9 (4): 426–431. doi:10.3201/eid0904.020417. PMC 2957981. PMID 12702221.
  2. ↑ Division of Foodborne, Waterborne, and Environmental Diseases (DFWED) Home. (2023). Enteric Diseases Epidemiology Branch. Washington, D.C.: Centers for Disease Control and Prevention.
  3. 1 2 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
  4. ↑ Centers for Disease Control and Prevention. (2023). Parasites Glossary. Retrieved from Parasites: https://www.cdc.gov/parasites/glossary.html#oocyst
  5. 1 2 Mac Kenzie WR, Hoxie NJ, Proctor ME, Gradus MS, Blair KA, Peterson DE, et al. (July 1994). "A massive outbreak in Milwaukee of cryptosporidium infection transmitted through the public water supply". The New England Journal of Medicine. 331 (3): 161–167. doi:10.1056/nejm199407213310304. PMID 7818640.
  6. ↑ Botkin DB, Keller EA (2005). Environmental Science: Earth as a Living Planet (5th ed.). p. 441. ISBN 978-0-471-48816-3.
  7. 1 2 Hoxie NJ, Davis JP, Vergeront JM, Nashold RD, Blair KA (December 1997). "Cryptosporidiosis-associated mortality following a massive waterborne outbreak in Milwaukee, Wisconsin". American Journal of Public Health. 87 (12): 2032–2035. doi:10.2105/ajph.87.12.2032. PMC 1381251. PMID 9431298.
  8. ↑ "Cryptosporidium in Milwaukee's water supply caused widespread illness". Infectious Disease News. No. September 2007. Healio. September 2007. Retrieved 22 February 2021.
  9. ↑ Osewe, P.; Addiss, D.G.; Blair, K.A.; Hightower, A.; Kamb, M. L.; Davis, J.P. (1996). "Cryptosporidiosis in Wisconsin: A case-control study of post-outbreak transmission". Cambridge University Press: 297–304.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  10. ↑ Kenzie, Mac; Schell, L.; Blair; Addiss; Peterson; Hoxie; Kazmierczak; Davis (1995). "Massive Outbreak of Waterborne Cryptosporidium Infection in Milwaukee, Wisconsin: Recurrence of Illness and Risk of Secondary Transmission". Infectious Diseases Society of America: 57–62.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  11. 1 2 Lewis, C. (2015, January 9). Superintendent of Milwaukee Water Works. (M. Gonzalez, & B. Gonzalez, Interviewers)
  12. ↑ Ceraso, M. (2013). 20 years after fatal outbreak, Milwaukee leads on water testing. Wisconsin Water Watch.
  13. ↑ 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

Further reading

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