CEE567 Exam 3 CHPTs 9-11

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waterborne disease outbreaks

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1

waterborne disease outbreaks

two or more persons must have experienced a similar illness after exposure to water and be epidemiologically linked by time and by location of exposure to water

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2

classifications of water-related illnesses

  • waterborne

  • water-washed

  • water-based

  • water-related

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3

waterborne

pathogens that originate in fecal material and are transmitted by ingestion (Cholera)

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4

water-washed

organisms that originate in feces and are transmitted through contact because of inadequate sanitation (shigellosis)

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5

water-based

organisms that originate in the water or spend part of their life cycle in aquatic animals and come in direct contact with human in water or by inhalation (Legionnaire's disease)

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6

water-related

microorganisms with life cycles associated with insects that live or breed in water (malaria)

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7

chemical definition of waterborne disease outbreak

at least one case of illness has occurred as a result of ingestion of water

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8

microbiological definition of waterborne disease outbreak

at least two cases of a disease that have occurred as a result of ingestion of water from a common source

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9

reporting of waterborne disease outbreaks

  • not mandatory

  • intensity of investigation varies from state to state and within states

  • under-reported

  • many outbreaks are not even recognized

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10

What percentage of US waterborne outbreaks are reported?

10 - 13%

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11

database of disease outbreaks

  • the CDC and EPA, and the Council of State and Territorial Epidemiologists have maintained a database of disease outbreaks in the U.S. since 1971

  • database was formulated on the responses to a voluntary reporting by state and local public health officials

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12

trends in waterborne outbreaks - deaths

  • from 1920-1990, deaths decreased to approximately 1/yr

  • increased after 1990

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13

reasons for death decrease from 1920 - 1990

  • improvements in treatment (filtration, chlorination)

  • improvements in medical care (antibiotics, vaccines)

  • general improvements in living conditions

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14

trends in waterborne outbreaks

no real decrease since 1920's (possible reasons: fewer outbreaks, but better recognition and reporting; increase in the number of individuals with weakened immune systems)

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15

water systems

  • community

  • non-community (transient and non-transient)

  • individual

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16

community water systems

water supplies serve at least 25 year-round residents or 15 service connections used by year-round residents

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17

non-community water systems

water supplies serve an average of at least 25 individuals for 60 or more days per year

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18

transient non-community water systems (TNCWS)

  • serve a changing population for a few times in a year (fewer than 25 of the same people over 6 months/year)

  • examples: parks, campgrounds, highway rest stops

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19

non-transient non-community water systems (NTNCWS):

  • serve a continuous population (25 or more people for at least 6 months/year) a small proportion of their supply

  • examples: industries, schools, factories

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20

water source in disease outbreaks

mostly groundwater and wells (72% from 1991 - 1994)

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21

virus outbreaks

waterborne enteric viruses caused 14% of outbreaks and 38% of illnesses in the United States from 1999 to 2002

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22

Milwaukee Cryptosporidium outbreak

  • March 1993

  • 403,000 ill individuals

  • 4,400 hospitalized individuals

  • 100 deaths (mostly individuals with weakened immune systems)

  • outbreak recognized when stores ran out of anti-diarrhea medicines

  • cause not identified for 2 weeks

  • isolated the oocysts from ice

  • water met all required standards

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Clark County, Nevada Cryptosporidium outbreak

  • 1994

  • 90 people ill

  • restricted to the AIDS community

  • 10 deaths

  • lasted 7 months

  • never isolated the organism in water

  • water met all required standards

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24

recommendations to prevent waterborne outbreaks & improve surveillance

  • focus on water system operations, management, water quality, and effective regulations to sustain gains made in the provision of safe drinking water

  • attention to address and prevent waterborne disease transmission in unregulated drinking water systems

  • reduce the risk for outbreaks in groundwater systems

  • understanding of the biology, ecology, and inactivation of Legionella in biofilm and premise plumbing

  • recognition and focus on premise plumbing and point-of-use issues

  • additional efforts to reduce the risk of outbreaks associated with drinking water distribution systems

  • prevention efforts in residential and recreational settings (e.g., campgrounds and parks) to reduce waterborne disease outbreaks

  • research to better characterize the burden of waterborne disease in the U.S. so that prevention actions can be prioritized and interventions to reduce waterborne disease can be developed

  • additional resources for outbreak detection and investigation of waterborne disease and outbreaks—including epidemiologic, environmental, and laboratory support—at local, state, territorial, and national levels

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25

routes of exposure to pathogens in water impacted by waste

  • water --> plants, recreation, aerosols, ingestion, animals

  • water is applied to a land surface, flows in the subsurface to groundwater, which is used as drinking water

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26

risk assessment

  • developed by the National Research Council (1983) to address chemical hazards in the environment

  • the framework was modified to address the associated health effects from environmental exposure to microorganisms

  • risk assessment methods have been long accepted in the regulatory arena and have been used for the examination of microbiological standards since 1989 and continue to be developed and accepted

  • process of estimating both the probability that an event will occur and the probable magnitude of its adverse effects over a specified time period

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risk

  • "possibility of experiencing harm from a hazard"

  • a function of the probability of an adverse health effect and severity of that effect

  • an inherent property of everyday human existence

  • a key factor in all decision making on almost all issues

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risk assessment process

  • involves evaluating likelihood/frequency of experiencing a risk

  • evaluates the likelihood that adverse ecological effects may occur or are occurring as a result of exposure to one or more stressors

  • the information on microbial pathogens or chemicals in the environment is critical in making decisions about potential risks and corrective actions

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risk assessment steps

  • hazard identification (hazard characterization)

  • exposure assessment (dose-response)

  • risk characterization

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risk analysis steps

  • risk assessment

  • risk management

  • risk communication

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microbial risk assessment

  1. hazard identification - What are the contaminants of concern? example: microbial pathogens of concern in stools of infected individuals

  2. exposure assessment - What quantity of the contaminant are we exposed to? example: microorganism Detection in Untreated Wastewater

  3. dose-response assessment - What dose of the organism is required to produce a response in the exposed individual? example: Cryptosporidium infectivity data

  4. risk characterization - What is the probability that an adverse response will occur in the exposed individual? (human illness or death) example: probability of infection for enteric microorganisms

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dose response

  • extrapolated from epidemiologic investigations

  • obtained by human feeding studies on healthy, young adult volunteers

  • best estimates based on a limited data base from outbreaks

  • worst case estimates

  • cannot be directly used to assess risk because of many variables (see Variables of the Host)

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variables of the host

  • age

  • general health

  • pregnancy

  • medications--OTC or prescription

  • metabolic disorders

  • alcoholism, cirrhosis, hemochromatosis

  • malignancy

  • amount of food consumed

  • gastric acidity variation: antacids, natural variation

  • genetic disturbances

  • nutritional status

  • immune competence

  • surgical history

  • occupation

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available dose-response models - bacteria

  • Salmonella

  • Shigella

  • enteropathogenic E. coli (E. coli 0157-H7 - animals)

  • Vibrio

  • Legionella

  • Campylobacter

  • Listeria

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available dose-response models - viruses

  • rotavirus

  • echovirus

  • coxsackievirus

  • adenoviruses

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available dose-response models - protozoans

  • Giardia

  • Cryptosporidium

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37

risk characterization

assumptions in risk calculations for exposure after artificial recharge:

  • virus inactivation rate: 0.043 log10 /day

  • vadose zone: 3 m

  • residence time: 6 months

  • exposure: 1 liter/day

  • treatment removal (unchlorinated: 0 log10; chlorinated: 3.9 log10; full: 5.2 log10)

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38

How do we set standards for pathogens?

In 1974 Congress passed Safe Drinking Water Act and EPA established standards for drinking water

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39

standards for chemicals

standards for many contaminants were set using a risk analysis approach

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standards for microbes

  • setting standards was more difficult for microbes because of the detection methods (difficult, costly and days to weeks for results)

  • therefore, Coliform bacteria was used, but in the 1980s it had become clear that coliform did not indicate the presence of viruses or Giardia, resulting in development of STR and ICR

  • regulations were established to protect public health, and not to be too troublesome to utilities

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41

Surface Treatment Rule (STR)

  • developed to ensure the microbial safety of drinking water

  • requires utilities that use surface waters to provide filtration and enough disinfection to kill viruses

  • goal of treatment was Giardia infection should not be greater than 1/10,000 (this value is close to the annual risk of infection from waterborne disease outbreaks in U.S. (4/1,000))

  • went into effect in 1991

  • required that all drinking water treatment plants be capable of removing 99.9% Giardia & 99.99% viruses

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42

Information Collection Rule (ICR)

developed by the EPA to assess whether the treatment required was enough to ensure 1/10,000 yearly risk

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43

risk management

  • evaluation of the need for the control of the risk and options for its control

  • includes consideration of social, political, and economic issues plus the engineering problems inherent in a proposed solution

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44

application of microbial risk assessment

  • development of standards and criteria

  • determine needed sensitivity of analytical methods

  • define treatment requirements

  • define quantitatively relative risks

  • evaluate the impact of low level of contamination or chronic exposure

  • determine cost of subsequent infection, illness and death

  • cost/benefit analysis

  • develop standards

  • define appropriate sampling methodologies

  • design appropriate treatment strategies

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45

what we have learned from quantitative microbial risk assessment

  • treatment plant variability in pathogen removal effects long term risk (i.e. 100% removal of all pathogens over time is not possible)

  • short term exposures can have a significant impact on risk to a community --> the more polluted the raw water source, the greater the need for treatment reliability

  • greatest Uncertainty in estimating risk is from exposure

  • no-dose response threshold for enteric viruses and parasites or the infectivity is so low it should be considered one organism

  • sensitive populations (greatest risk of serious illness and death) represents 20% of U.S. population and is increasing

  • sequelae are common and have a significant impact on the quality of life

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major driving factors

  • development of molecular methods for detection of pathogens

  • fingerprinting of microbes

  • Quantitative Microbial Risk Assessment

  • increased importation of food products from the developing world

  • less Tolerance of Risk (Greater public awareness of microbial threats)

  • changing Demographics (Older population - Increase in immuno-compromised individuals)

  • changes in Water Supply and Treatment (use of more contaminated sources; treatment process allows greater barrier penetration)

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47

primary standards

  • based on health considerations

  • established by the EPA, enforced by states

  • protect from: toxic chemicals, radioactive elements, pathogens

  • maximum Contaminant Level (MCL)

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secondary standards

  • for contaminants that cause offensive taste, color, odor, staining, foaming, etc. (do not make people sick)

  • not enforced

  • guidelines for treatment plant operators

  • examples: sulfate, iron & color

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49

Safe Drinking Water Act (SDWA)

  • passed by Congress in 1974

  • amended twice in 1986 and 1996

  • amendments led to announcement of stage 1 & stage 2 Disinfectants & Disinfection Byproducts (DBPs) Rule

  • EPA has regulated 3 disinfectants and 11 chlorinated by-products at federal level

  • there are many more unregulated DBPs and some are listed in EPA's candidate contaminant list 5 (CCL5) such as 5 different forms of nitrosamines

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Disinfectants & Disinfection Byproducts (DBPs) Rule

  • established by EPA

  • aimed to lessen the risk of chlorinated by products

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51

pre-1985 microbial standards

total coliform bacteria concentration: less than or equal to 2.2 per 100 ml

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1985 microbial standards

  • MCLGs established

  • total coliform bacteria - 0 per 100 mL

  • viruses - 0

  • Giardia - 0

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53

Surface Water Treatment Rule (1989)

  • surface waters must be filtered and disinfected to achieve 99.9% removal (3-log removal) of Giardia and 99.99% removal (4-log removal) of viruses

  • combined filter effluent (CFE) turbidity 0.5 NTU

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54

Total Coliform Rule (1990)

  • MCL: 0 per 100 ml

  • presence-absence test

  • <5% samples can be positive

  • repeat samples required for analysis of fecal coliform bacteria

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55

Interim Enhanced (1998) and Long Term 1 E. SWTR (2002)

  • 2-log Cryptosporidium removal/inactivation

  • CFE 0.3 NTU & individual filter monitoring requirements

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56

Stage 1 DBP Rule

  • TTHM 80 μg/L and HAA5 60 μg/L

  • compliance based on system averages

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Stage 2 DBP Rule

  • TTHM 80 μg/L and HAA5 60 μg/L

  • compliance based on each location

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58

Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) (2006)

  • up to 2.5-log additional removal/inactivation for filtered systems (compared to STWR, meaning a total of 5.5-log removal)

  • up to 3-log inactivation for unfiltered systems

  • 3 - 5.5-log Cryptosporidium removal/inactivation based on source concentration and source water monitoring

  • objective: provide additional protection from pathogens and balance the risks presented by microbial pathogens & DBPs

  • one of the most recent rules in the M & DBP cluster

  • cover the reservoir or provide 4-log virus, 3-log Giardia, and 2-log Cryptosporidium removal/inactivation after the reservoir

  • reduces disease incidence associated with Cryptosporidium and other pathogens in drinking water

  • supplements SWTR regulations by targeting additional Cryptosporidium treatment requirements to higher risk systems

  • contains provisions to mitigate risks from uncovered finished water storage facilities and to ensure that systems maintain microbial protection as they take steps to reduce the formation of DBPs

  • no more system average (every sample must meet DBP concentration and microbial concentrations)

  • latest and greatest drinking water rule

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monitoring requirements

  • 24 months Cryptosporidium monitoring

  • bin class based on average concentration during monitoring

  • For all unfiltered systems and small filtered systems (serving <10,000) the average is the mean of all samples

  • for large filtered systems (serving >10,000), the average differs by the number of samples collected

  • 24 to 47 samples: highest 12 month running annual average

  • 48 samples or higher: mean of all samples

  • historical data (grandfathered data) that meets QA/QC requirements may be used in lieu of additional monitoring

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60

ground water systems (GWR)

  • consist of community, non-transient, non-community, and transient, non-community water systems

  • 70-110 million people drink groundwater daily from public supplies in the US

  • ground water systems implicated in about half of all microbial disease outbreaks

  • ground water systems have >90% of all coliform MCL violations

  • microbial contaminants include viruses, bacteria, sometimes protozoa

  • risk assessments suggest more than 7 million illnesses/year from GW systems

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Ground Water Rule

  • proposed draft rule - July 1992

  • all public ground water supplies must disinfect

  • a disinfectant residual must be maintained

  • disinfection may be avoided if certain criteria are met

  • GW Rule 2014: requires all public groundwater systems to evaluate their existing disinfection system prior to the first customer to achieve a minimum of 4-log virus inactivation

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proposed GWR provisions

  • periodic sanitary surveys

  • hydrogeologic sensitivity assessments

  • source water monitoring (state selects one of the following fecal indicators: E. coli (7 analytical methods), Enterococci (3 analytical methods), or Coliphage (2 analytical methods: 1601 and 1602))

  • corrective action

  • compliance monitoring

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Ground Water Rule source water monitoring provisions

  • routine monitoring: system that draws water from "sensitive" aquifer must monitor monthly for at least one year

  • triggered monitoring: system that has a total coliform-positive sample must collect and analyze 1 source water sample within 24 hrs

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64

MCLGs

  • Maximum Contaminant Level Goals

  • established because the present treatment technology is not able to meet the MCLGs but should be able to within a few years

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microbial removal

  • filtration removes lots of bacteria but not lots of viruses

  • viruses are mostly removed during disinfection

  • microbes are inactivated/removed during each step of the conventional drinking water treatment process (coagulation, flocculation, sedimentation, filtration, disinfection)

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balancing chemical and microbial risks

  • lowering chlorine concentrations during disinfection is important to reduce disinfection by-product (DBP) formation

  • decreasing DBP formation can be done by increasing contact time (less chlorine needed for CT value to be met) or using UV light to disinfect

  • storage tanks are used to increase contact time

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