CEE567 Exam 3 CHPTs 9-11

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waterborne disease outbreaks

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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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classifications of water-related illnesses

  • waterborne

  • water-washed

  • water-based

  • water-related

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

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

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

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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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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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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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What percentage of US waterborne outbreaks are reported?

10 - 13%

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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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trends in waterborne outbreaks - deaths

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

  • increased after 1990

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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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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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water systems

  • community

  • non-community (transient and non-transient)

  • individual

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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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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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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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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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water source in disease outbreaks

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

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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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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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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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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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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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  • "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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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  • 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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