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Relationships Between Human Demographics, Environment/Land Use, Infrastructure, and Disease: Lessons from the Massive Waterborne Outbreak of
Cryptosporidium Infections, Milwaukee, 1993
Jeffrey P. Davis, MDWisconsin Division of Public Health
Global Issues in Water, Sanitation and Health Forum on Microbial Threats
Institute of MedicineSeptember 23- September 24, 2008
Milwaukee: Tuesday, April 5, 1993Reports of increased school and workplace absenteeism from local health departments in Milwaukee County
Apparent widespread gastroenteritis
Increase in testing stool specimens for bacterial enteric pathogens in several hospital laboratories: negative results
Wisconsin Division of Health will conduct on site investigation
Milwaukee: Wednesday, April 7, 1993Wisconsin Division of Health staff on site
Unprecedented increases in turbidity of treated water at southern Milwaukee Water Works water treatment plant
Milwaukee Health Department laboratories: Cryptosporidium detected in stool specimens previously negative for bacterial enteric pathogens: 7 adults plus one other adult with Cryptosporidium detected in another lab
Milwaukee Mayor issues boil water advisory
Water treatment process Milwaukee Water Works, 1993
Change in coagulant
Aging water distribution infrastructure: concern regarding leaching of lead and copper if pH was too low
September, 1992: change in coagulant from alum to polyaluminum chloride (PAC)
Theories on why this massive outbreak occurred: a perfect storm
Compelling confluence of likely contributing factors and events: unique opportunities to dramatically amplify case occurrence
•South Plant intake grid location•Unusual weather conditions•Cross connection between sanitary and storm sewer•Change in water treatment coagulant •Human amplification•Limited testing prior to outbreak recognition
Theories on why this massive outbreak occurred: a perfect storm
•South Plant intake grid location•Unusual weather conditions•Cross connection between sanitary and storm sewer•Change in water treatment coagulant •Human amplification•Limited testing prior to outbreak recognition
Theories on why this massive outbreak occurred: a perfect storm
•South Plant intake grid location•Unusual weather conditions•Cross connection between sanitary and storm sewer•Change in water treatment coagulant •Human amplification•Limited testing prior to outbreak recognition
High flow and unusual weather conditions
Unusually high snowpack during winter that melted rapidly while frostline still high
Runoff included manure spread on snow (widespread practice)
Record setting rainfall during March and April
High flow and unusual weather conditions (continued)
Record setting rainfall during March and April:•Storm sewer overflows in Milwaukee•Sewage disinfected but bypassing treatment at MMSD facility before emptying into Lake Michigan•Runoff in river watersheds
Unusual wind conditions and direction :•Northeasterly which likely accentuated southerly flow of water within breakfront and out the south fair weather gap•Amplified plumes flowing directly toward intake grid
Theories on why this massive outbreak occurred: a perfect storm
•South Plant intake grid location•Unusual weather conditions•Cross connection between sanitary and storm sewer•Change in water treatment coagulant •Human amplification•Limited testing prior to outbreak recognition
Cross connection between a sanitary sewer and a storm sewer
Early March: linkage of storm sewer draining newly constructed soccer fields with main sewer that drains into the Menomonee River
Animal enteric organs, rubber rings
Detection of cross connection between abattoir kill floor sanitary sewer and storm sewer
Multiple week cleaning process
Redirection of sanitary sewer sewage
Release of Cryptosporidium oocysts: ?? •Directly through storm sewer into river during or preceding events•Bolus of oocysts properly flowing through sanitary sewer during clean-up with potential bypass of treatment during high flow interval
Theories on why this massive outbreak occurred: a perfect storm
•South Plant intake grid location•Unusual weather conditions•Cross connection between sanitary and storm sewer•Change in water treatment coagulant•Human amplification•Limited testing prior to outbreak recognition
Change in coagulant
September, 1992: change in coagulant from alum to polyaluminum chloride (PAC)
Inexperience dosing system with PAC in response to spikes in finished water turbidity, particularly during such extenuating circumstances
Resumption of use of alum as the coagulant on April 2 was too late
Theories on why this massive outbreak occurred: a perfect storm
•South Plant intake grid location•Unusual weather conditions•Cross connection between sanitary and storm sewer•Change in water treatment coagulant •Human amplification•Limited testing prior to outbreak recognition
Human amplificationCritical factor
Small number of Cryptosporidium oocysts (median infectious dose: 132 oocysts) needed to cause human infection
Billions of oocysts excreted each day in stools of symptomatic humans; persistent excretion after symptoms resolve
Oocysts can remain infective in moist environment for 2-6 months
Opportunity for infection in this outbreak was inordinately high: sustained vicious cycle
Theories on why this massive outbreak occurred: a perfect storm
•South Plant intake grid location•Unusual weather conditions•Cross connection between sanitary and storm sewer•Change in water treatment coagulant •Human amplification•Limited testing prior to outbreak recognition
Limited testing for Cryptosporidium infection prior to outbreak recognition
Typically requested individuals with HIV infection who were experiencing diarrhea
Small number of tests per month
Not routine component of O&P testing, required additional requisition
Additional pelleting and staining procedure required
Insufficient testing demand may have delayed outbreak recognition
Lessons learned from the massive waterborne outbreak of Cryptosporidium infections, Milwaukee, 1993
There were manyHere are some
Lessons learned 1993: Stringent water quality standards
Maximize the use of stringent water quality standards–More critical than testing for Cryptosporidium–At the South Plant measured turbidity and other water quality indices were within state and federal regulatory standard limits–Turbidity is more than an aesthetic feature of finished water
Strive to use the most appropriate technical advances–Maximize drinking water safety–Minimize response time to events
Lessons learned 1993: environmental testing for Cryptosporidium
Laboratory testing for Cryptosporidium in water, sewageand the environment is limited
–Small number of laboratories and expertise–Labor intensive, insensitive tests–Lengthy time to proficiency
Sampling process is lengthy and not standardized–Equipment and techniques vary–influences data quality and interpretation
Lessons learned 1993: environmental studies
Wanted: a coordinated plan to investigate the environment when waterborne outbreaks of Cryptosporidium infection occur
–Delineate general principles–Interagency cooperative responses should be readily dispatched –Federal leadership is needed
Appropriate environmental studies relevant to human health
–Complex to design and coordinate–Costs to adequately test and sample are high–Difficult to mobilize–Limited quality of assays–Absence of surrogate markers for Cryptosporidium
Lessons learned 1993: surveillance
Public health surveillance for and reporting of human Cryptosporidium infections is important
Watery diarrhea is a good case definition for Cryptosporidium infection in an outbreak setting
Random digit dialing surveys are valuable to assess scope and progress of large community outbreaks
Nursing home populations are relatively geographically fixed and readily accessible: valuable in our investigation
Lessons learned 1993: testing of human stool
Cryptosporidium infections are underdiagnosed and underrecognized
–insufficient tests, insufficiently sensitive–no reliable serologic test
Assays for Cryptosporidium are not routine tests in parasitogoic testing of human stool
–Broaden index of suspicion for Cryptosporidium infections–Routine testing for Cryptosporidium in O&P examinations
Interest in Cryptosporidium testing is difficult to sustain–Additional process, additional costs
Lessons learned 1993: communication
Interagency communication and working closely with communities of individuals at greatest risk of serious illness are critical
Public health messages had not been developed or consensus regarding messages had not been achieved
Lack of guidelines and insufficient understanding of public health significance for governmental response to findings of:– Cryptosporidium oocysts (particularly small numbers) in
finished water– Increased turbidity of finished water– Elevated particle counts in finished water
Lessons learned 1993: the media
Media (electronic and print) are essential to:
–Communicating risks–Communicating other important public health messages–Facilitating needed inquiry
Media: prominent role in conveying information regarding drinking water quality to all those who need to know
Massive Waterborne Outbreak of Cryptosporidium Infections, Milwaukee, 1993: Contributors
Wisconsin: Division of Public Health, Department of Natural Resources, Department of Agriculture Trade and Consumer Protection, State Laboratory of Hygiene
Milwaukee: Health Department, Water Works, City Engineers, Metropolitan Sewer District,
Federal: Centers for Disease Control and Prevention, Environmental Protection Agency
American Water Works Service Co.
University of South Florida College of Public Health
Many other local, regional and state health departments