Monitoring for Pathogenic Microorganisms in the Venice Lagoon: Components for Modeling and Risk Asse

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Monitoring for Pathogenic Microorganisms in the
Venice Lagoon Components for Modeling and Risk
Assessment

• Troy M. Scott, Ph.D.
• University of South Florida, USA

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Outline

• 1. Overview of microbiological contaminants
• 2. Routes of exposure and health outcomes
• 3. Monitoring programs Benefits and Limitations
• 4. Survival Characteristics of Pathogens and
• Indicators
• 5. Microbial Risk Assessment

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Pathogens of Concern

• Domestic sewage contains many microscopic,
  pathogenic organisms
• Many strict human pathogens (Shigella spp.,
  Salmonella enterica ser. Typhi, Hepatitis A,
  etc.)
• Of particular concern are the protozoan parasites
  (Cryptosporidium and Giardia) and Enteric
  Viruses.

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Human Enteric Viruses

• Over 100 different types can be excreted in human
  feces
• Low infective dose
• Cause gastroenteritis, myocarditis, respiratory
  disease, encephalitis, paralysis
• More resistant than bacteria to environmental
  conditions and disinfection

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Enteric Protozoa

• Cryptosporidium and Giardia of particular concern
• Cause mild to severe gastroenteritis
• Cryptosporidiosis can be fatal in young, elderly,
  and immunocompromised
• Low infective dose (10)
• Oocysts and cysts extremely resistant to
  environmental conditions and disinfection

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Routes of Exposure

• Direct contact (ingestion) of contaminated water
  during recreational or commercial activities
• Eating raw or partially cooked shellfish

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Shellfish Consumption

• Many studies have linked consumption of raw or
  partially cooked shellfish with viral disease.
• Usually viral in nature, although indigenous
  bacteria (V. parahaemolyticus) are known to
  bioaccumulate in oysters.
• Cooking shellfish may not be sufficient to reduce
  risk of viral infection.

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Risk Associated with Consumption of Raw Shellfish

• Data on bioaccumulation and fate of viral and
  bacterial pathogens in shellfish is incomplete
• Thorough risk assessment linking sewage
  contamination to consumption of shellfish is not
  feasible

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Monitoring for Microbial Indicators Benefits
and Limitations

• Pathogenic microorganisms are often present in
  low numbers
• Many have a low infective dose
• Methods to detect pathogenic microbes often lack
  sensitivity
• Therefore, prediction of presence of pathogens
  often accomplished by monitoring for indicator
  organisms

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Characteristics of an ideal indicator organism

• Intestinal microorganisms
• Non-pathogenic
• rapidly detected
• easily enumerated
• present in high numbers
• possess survival similar to those of pathogens
  they predict

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Current Methodology

• Traditional and alternative microbial indicators
  have been used for many years to predict the
  presence of fecal pollution in water
• Total coliforms
• Fecal coliforms
• Enterococci

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Current USEPA and Florida DOH Suggested Water
Quality Guidelines

• USEPA- freshwater E. coli 126 CFU/100mL
• Enterococci 33 CFU/100mL
• USEPA- marine waters Enterococci 35
  CFU/100mL
• FLDOH- total coliforms 1000 CFU/100mL
• FLDOH- fecal coliforms 200 CFU/100mL

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Limitations of Indicator Organisms

• Variable survival rates
• Inability to predict the presence of enteric
  viruses and protozoa
• Failure to predict presence of harmful aquatic
  organisms (e.g. toxic algae)
• Rarely effective in predicting health risks
  associated with consumption of shellfish

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Methods of Detection of Indicators and Pathogens

• Bacterial Indicators Relatively easy and
  inexpensive to assay. Many approved
  culture-based protocols
• Protozoa Filtration, Concentration by IMS,
  Staining by IFA, Enumeration by microscopic
  examination (Viable and nonviable)
• Cryptosporidium cell culture viability assay
• Enteric Viruses Filtration, Concentration by
  flocculation, Inoculation onto tissue culture,
  observation of cytopathic effects (CPE)

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Alternative Molecular Methods

• Many molecular methods also available to detect
  pathogens of concern
• Most are PCR-based
• Detect viable and nonviable organisms
• For viruses and protozoa, can be coupled with
  cell culture to better assess viability

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Survival of Pathogens and Indicators in Marine
Environment

• Specific pathogens have significantly different
  survival characteristics in marine environment
• In general Cryptosporidium gt enteric viruses gt
  Giardia gt Vegetative Bacteria
• Water temperature significantly affects survival
• Other factors include pH, salinity, UV, predation

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Data Compilation Microbial Risk Assessment

• Microbial Risk Assessment requires a significant
  amount of data
• Concentrations of pathogens often too low in
  receiving waters to accurately predict exposure
• Can be augmented by modeling techniques

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4 Steps of Risk Assessment

• Hazard Identification Describes acute and
  chronic human health effects associated with any
  particular hazard
• Dose-Response Characterizes the relationship
  between various doses administered and subsequent
  health effects
• Exposure Assessment Determines the size and
  nature of the population exposed and the route,
  amount, and duration of exposure
• Risk Characterization Integrates the
  information from exposure, dose response, and
  health steps to estimate magnitude of health risks

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Define Environments of Concern
Define Human Population Exposed
Compile Lists of Pathogens Expected in Environment
Define Expected Survival or Growth in Environment
Exposure and Dose Response
Risk Characterization
Risk Management
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ROUTES OF TRANSMISSION
Wastewater
Land Surface
Surface Water
Ground Water
Aerosols
Domestic use
Crops
Domestic use
Ingestion
Recreation
New Human Host
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Approaches to Microbial Risk Assessment

• Monitor for indicator organisms (Fecal coliforms,
  Enterococci) in raw wastewater and receiving
  waters
• Model fate and transport to estimate
  concentrations in receiving waters
• Concentrations in input
• Survival/die-off
• Compare to levels generally regarded as safe
• Provides an index of potential risk, not
  definitive risk assessment

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Approaches to Microbial Risk Assessment

• Risk associated with ingestion of enteric viruses
  or protozoa
• Concentrations of viruses and protozoa can be
  determined in raw wastewater
• Fate and transport models can be used to estimate
  exposure levels
• Exposure can be coupled with infectivity and
  dose-response data to estimate risk

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Microbial Exposure Assessment

• Key differentiating characteristic of
  microorganisms is that microbes are discrete
  particles at sufficiently low density and
  statistics of their distribution must be
  considered.
• Easier to determine for specific risk assessment
  where concentrations and exposures can be
  quantified

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Microbial Dose-Response

• Develop relationship between level of microbial
  exposure and likelihood of adverse health
  response
• Two key differences between risk posed by
  microorganisms and other chemicals
• Population will receive distribution of actual
  doses (different from chemicals which are present
  at higher relative concentrations and evenly
  distributed)

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Microbial Dose-Response

• Second distinguishing aspect is the ability of
  microorganisms to propagate once introduced into
  a host
• Disease process represents an overcoming of host
  defense systems

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Microbial Dose-Response

• Therefore, the process of infection may be
  considered as requiring two sequential processes
  to occur
• The human host must ingest one or more organisms
  capable of causing disease
• The organisms undergo decay or are impaired from
  multiplying, and only a fraction of organisms
  reach site of infection

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Models for Risk Assessment

• Exponential Dose-Response Model
• Assumes random distribution of microorganisms
• Each organism has independent and identical
  survival capability
• Minimum number of organisms required for
  infection is one
• P 1 e(-rN)
• Where N Exposure
• r is determined from dose response data

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Models for Risk Assessment

• Beta-Poisson Dose-Response Model
• Modifies the exponential model by allowing for a
  distribution of microorganism-host interaction
  probabilities
• P1-(1N/b)-a
• Where N Exposure
• a and b determined from dose-response data

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Summary of Risk Assessment

• Hazard Identification
• Giardia, Cryptosporidium, Enteric Viruses
• Dose Response
• Exposure Assessment
• Routine monitoring, Fate/Transport modeling
• Estimation of exposure through direct contact,
  recreational waters, drinking water
• Risk Assessment

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Summary

• Pathogens in wastewater and fecally-contaminated
  water may result in significant risk to human
  health
• Risk of infection may exist in waters containing
  acceptable levels of indicator organisms
• Specific pathogens of interest are difficult and
  expensive to monitor in environmental waters
• Specific pathogens exhibit variable survival
  characteristics and may be accumulated in
  shellfish
• Sufficient data must be collected on
  concentrations of protozoa and viruses in raw
  wastewater in order to conduct thorough risk
  assessment
• Comparison of indicator concentrations to
  recommended guidelines , can also be used to
  predict an assessment of risk associated with
  direct contact with surface water