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