Safe Water: Walkerton

Lecture by: G. Blank

Notes by: K. Blanchette

 

E. coli 0157: H7

  • Strain of E. coli which is normally present and harmless.
    • Most commonly found in beef and dairy cattle (primary reservoir) and to a lesser extent pigs, chickens, goats, sheep, and deer
  • Microbiology: Gram negative bacterium; facultative anaerobe.
  • Acid tolerant: Therefore, unpasteurized fruit juices can make you sick!
  • Virulent strain < 10 cells which is important to understand, it means that you don't need a lot of these cells to make you sick.

 

Enteric Disease

  • Undercooked ground beef and less frequently unpasteurized milk are well recognized vectors
  • Outbreaks and clusters peak during the warmest months
  • Very young (2-10 years old) and elderly are most susceptible to sever illness and complications.

 

0157: H7 Illness

  • Spectrum of human illness:
  • Initial symptoms: Non-bloody diarrhea and severe abdominal cramps. However, may be asymptomatic (e-coli still being shed through feces of infected individuals).
    • 3-4 day incubation period (2-12 days)
    • Colonization of the large bowel
  • After 2-3 days of illness the infected individual may develop bloody diarrhea (Hemorrhagic Colitis) for 4-10 days. This condition is self limiting usually after one week.
  • Enterotoxins travel by blood and affects kidneys causing Hemolytic Uremic Syndrome (HUS). This occurs in about 5-6% of patients with HC.
    • About half of these people require dialysis
    • 75% require transfusions
    • Case fatality is about 1%
    • This is the leading cause of acute renal failure in children
  • E. coli can be transmitted through four ways, listed in order of most common to least common
    • Ground Beef
    • Person-to-person
    • Vegetables and fruit
    • Water
  • Outbreaks
    • Canadian average for E. coli 0157: H7 infections is about 3.36/100,000
    • Manitoba average is about 4. 87/ 100, 000

 

Cattle Carriage

  • 1998: contamination in cattle on farms and abattoirs was found <0.3 to 3%
  • 1999: isolation of E. coli 0157: H7 from 7.5% of fecal samples collected from cattle at time of slaughter.
  • Bacterium colonizes the Gastrointestinal Tract of cattle.
! Note: E. coli is found on cattle Hyde. Therefore, de-hiding cattle can cause a transfer of the organism to previously sterile tissue.
  • Cattle receive E. coli from feed, water, and other cows.
  • Infected cows may appear perfectly normal

 

Survival in Poop

  • E. coli is easily destroyed by heat (pasteurization) and chlorination
  • Zoonotic pathogen
  • In controlled laboratory experiments:
    • 100 days in bovine manure @ -20 °C
    • 100 days in ovine manure @ 4 or 10 °C
    • 70 days @ 5°C
    • 56 days @ 22°C
    • 49 days @ 37°C
  • Note: This is survival not reproduction.
  • Decimal Reduction Time (DRT) is the time it takes to reduce the organism population by 90%
    • At 4°C it takes 21.5 days
    • At 20°C it takes 14.8 days
    • At 37°C it takes 3.2 days
  • In non-aerated ovine manure piles exposed to the environment E. coli survived for more than one year
  • In Aerated ovine it survived 4 months
  • Aerated bovine the organism survived 47 days
  • At temperatures of 4-6°C most pathogens can survive for at least one month.

 

Survival in Soil

  • E. coli left 1.3 to 1.7 days on grass pasture was detected in soil 16 to 63 days later.
  • Survival in Soil is dependent on three factors
    • Temperature and UV: As temperature increases the number or organisms decrease.
    • Moisture: Dry soil increases the number of organisms
    • Soil Type: Sandy, clay soil has higher concentrations of E. coli

 

Factors affecting survival in Poop

      1. Storage Temperature
      2. Aeration
      3. Competitive MO
      4. Moisture
      5. Composition including pH

 

Waterborne Transmission

  • Known vectors for the transmission of pathogenic bacteria, viruses and protozoa are as follows: drinking water, water used for food production, irrigation, fish farming, waste water, surface water and recreational water.
  • Pathogenic bacteria, viruses, and protozoa include: salmonella Typhi, Shigella dysenteriae, Vibrio cholerae, Cryptosporidium parvum, Giardia lamblia

 

Contamination of Water

  • Tends to be episodic: It is more common in the summer
  • Increased risk with overflow or seepage of sewage
  • Increased risk due to surface water runoff
  • Increased risk due to flooding over the well field
  • Contamination is possible through poorly maintained wells
  • Surface water (lakes) poses more risk compared to ground water due to pollution

 

Survival in Water

  • Greatest survival in filtered, sterile municipal water
  • Least survival in lake water
  • Survival is greatest at lower temperatures

 

Waterborne Outbreaks

  • Outbreaks have increased in recent years. Outbreaks occur from:
    • Swimming water and water parks
    • Drinking contaminated water
    • Unchlorinated wells
    • Ice
  • Contaminated water has the potential to cause extensive outbreaks due to the large population served.

 

ABC's of safe drinking water

*very important, if the following were respected the tragedy in Walkerton would have been avoided!
  1. Good source of water
  2. Effective treatment
  3. Secure distribution system
  4. Continuous monitoring
  5. Appropriate response to adverse results

 

Walkerton Tragedy

  • May 15, 2000
  • Residents of the town experience bloody diarrhea and gastrointestinal distress
  • DNA typing strains from manure match human isolates of E. coli and Campylobacter
  • 7 dead
  • 14 die of complications related to E. coli
  • 2, 300 (40%) get sick
  • Ontario Clean Water Agency put in charge

 

Walkerton

  • April 2000
  • 70 tonnes of cattle manure was spread on Stonegate farm
  • Stonegate farm is located close to Walkerton well #5
  • Shallow well
  • Water was drawn from very shallow area 5.4 to 7.7 m below surface
  • Heavy storms hits region (May 8-12)
  • Manure seeps into well
  • Water should be filtered and Cl2
  • Piping for chlorination not installed

 

Walkerton

  • Initial pump tests in 1987 indicated fecal coliforms
  • August 2000 well pumped out E. coli
    • Used less chlorine than required
    • Organic contamination reduced free chlorine
    • 5 soil samples from 23 boreholes around the well were positive
  • Water drawn from area enclosed by fractured bedrock yielded rock channels
  • Government: use chlorine in a concentration high enough to sustain a residual of 0.5 mg/ L after 15 min contact time yield 99% destruction

 

Walkerton

  • Proper chlorine dose yields a 7 log (10,000,000 to 0) reduction by 0.25 mg/L within one min
  • Operators did not continuously monitor chlorine or turbidity or microbiology
  • Monitors could have sounded an alarm and shut off pumps to the well
  • Also, no day to day monitoring
  • Operators falsified records
  • Misstating locations at which microbiological samples were taken

 

Culpable

  • Although guidelines were in place the Ontario government was blamed for not regulating water quality and enforcing those guidelines.
  • One of the operators responsible received one year in prison and the other operator responsible received nine months of house arrest.
  • Note: Post Walkerton all water samples are now sent to an accredited lab.