Epidemiology ii
Download
1 / 50

- PowerPoint PPT Presentation


  • 160 Views
  • Uploaded on

Epidemiology II. ENVR 890-Sec. 003/ENVR 296-Sec. 003 Mark D. Sobsey With material from Prof. Jack Colford, UC-Berkeley Dr. Steve Luby, ICDDR,B Joseph Eisenberh, U. of Michigan. Using Epidemiology for Microbial Risk Analysis. Problem Formulation what’s the problem?

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about '' - kesia


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Epidemiology ii l.jpg

Epidemiology II

ENVR 890-Sec. 003/ENVR 296-Sec. 003

Mark D. Sobsey

With material from

Prof. Jack Colford, UC-Berkeley

Dr. Steve Luby, ICDDR,B

Joseph Eisenberh, U. of Michigan


Using epidemiology for microbial risk analysis l.jpg
Using Epidemiology for Microbial Risk Analysis

Problem Formulation

  • what’s the problem?

  • determine what infectious disease is posing a risk

  • its clinical features

  • causative agent

  • routes of exposure/infection

  • health effects

    (This is sort of like a preliminary QMRA, especially for exposure and health effects analyses)


Using epidemiology for microbial risk analysis3 l.jpg
Using Epidemiology for Microbial Risk Analysis

Exposure Assessment

  • how

  • how much

  • when

  • where and why exposure occurs

  • vehicles

  • vectors

  • doses

  • loads


Using epidemiology for microbial risk analysis4 l.jpg
Using Epidemiology for Microbial Risk Analysis

Health Effects Assessment

  • Human clinical trials for dose-response

  • field studies of endemic and epidemic disease in populations


Using epidemiology for microbial risk analysis risk characterization l.jpg
Using Epidemiology for Microbial Risk Analysis Risk Characterization

Epidemiologic measurements and analyses of risk:

  • relative risk

  • risk ratios

  • odds ratios

  • regression models of disease risk

  • dynamic models of population disease risk

  • Other disease burden characterizations:

    • relative contribution to overall disease burdens

    • effects of prevention and control measures and interventions

    • economic considerations (monetary cost of the disease, cost effectiveness of prevention and control measures)


  • Elements that may be considered in risk characterization l.jpg
    Elements That May Be Considered in Risk Characterization Characterization

    • Evaluate health consequences of exposure scenario

      • Risk description (event)

      • Risk estimation (magnitude, probability)

    • Characterize uncertainty/variability/confidence in estimates

    • Conduct sensitivity analysis

      • evaluate most important variables and information needs

    • Address items in problem formulation (reality check)

    • Evaluate various control measures and their effects on risk magnitude and profile

    • Conduct decision analysis

      • evaluate alternative risk management strategies



    Some more epidemiological terms and concepts l.jpg
    Some More Epidemiological Terms and Concepts Assessment for Waterborne Disease

    • Outbreaks: two or more cases of disease associated with a specific agent, source, exposure and time period

    • Epidemic Curve (Epi-curve): Number of cases or other measure of the amount of illness in a population over time during an epidemic

      • Describes nature and time course of outbreak

      • Can estimate incubation time if exposure time is known

      • Can give clues to modes of transmission: point source, common source, and secondary transmission


    Some more epidemiological terms and concepts epidemic curves l.jpg
    Some More Epidemiological Terms and Concepts: Epidemic Curves

    # cases

    # cases

    Time

    Time

    Common Source

    Point Source


    Additional analyses of health effects health effects assessments l.jpg
    Additional Analyses of Health Effects: CurvesHealth Effects Assessments

    • Health Outcomes of Microbial Infection

    • Identification and diagnosis of disease caused by the microbe

      • disease (symptom complex and signs)

      • Acute and chronic disease outcomes

      • mortality

      • diagnostic tests

      • DALYs

    • Sensitive populations and effects on them

    • Disease Databases and Epidemiological Data


    Databases for quantification and statistical assessment of disease usa l.jpg
    Databases for Quantification and Statistical Assessment of Disease - USA

    • National Notifiable Disease Surveillance System

    • National Ambulatory Medical Care Survey

    • International Classification of Disease (ICD) Codes

    • Other Databases

      • Special surveys

      • Sentinel surveillance efforts

    • Resources for disease surveillance vary greatly by country.

      • WHO and other international health entities assist countries lacking capacity for disease surveillance to obtain such data in various ways

      • Tracking is poor for some diseases, such as gastroenteritis and its specific causative agents (etiologies)


    Methods to diagnose infectious disease l.jpg
    Methods to Diagnose Infectious Disease Disease - USA

    • Symptoms (subjective: headache, pain) and Signs (objective: fever, rash, diarrhea)

    • Clinical diagnosis: lab tests

      • Detect causative organism in clinical specimens

      • Detect other specific factors associated with infection

    • Immune response

      • Detect and assay antibodies

      • Detect and assay other specific immune responses


    Health outcomes of microbial infection l.jpg
    Health Outcomes of Microbial Infection Disease - USA

    • Acute Outcomes

      • Diarrhea, vomiting, rash, fever, etc.

    • Chronic Outcomes

      • Paralysis, hemorrhagic uremia (HUS), reactive arthritis, Guillain-Barre Syndrome, etc.

    • Hospitalizations

    • Deaths


    Outcomes of infection process to be quantified l.jpg
    Outcomes of Infection Process Disease - USAto be Quantified

    Exposure

    Infection

    Asymptomatic Infection

    Advanced Illness, Chronic Infections and Sequelae

    Disease

    Acute Symptomatic Illness: Severity and Debilitation

    Sensitive Populations

    Mortality

    Hospitalization


    Morbidity ratios for salmonella non typhi l.jpg
    Morbidity Ratios for Disease - USASalmonella (Non-typhi)



    Health effects outcomes e coli o157 h7 l.jpg
    Health Effects Outcomes: InfectionsE. coli O157:H7



    Sensitive populations l.jpg
    Sensitive Populations Infections

    • Infants and young children

    • Elderly

    • Immunocompromised

      • Persons with AIDs

      • Cancer patients

      • Transplant patients

    • Pregnant

    • Malnourished





    Waterborne outbreak attack rates usa l.jpg
    Waterborne Outbreak Attack Rates- USA Groups with Adenovirus Infection


    Waterborne outbreak hospitalizations usa l.jpg
    Waterborne Outbreak Hospitalizations - USA Groups with Adenovirus Infection


    Slide25 l.jpg

    Predicted Waterborne Cryptosporidiosis in NYC in AIDS Patients Compared to the General Population

    Perz et al., 1998, Am. J. Epid., 147(3):289-301


    Slide26 l.jpg
    Assessing Risk from Environmental Exposure to Waterborne Pathogens: Use of Dynamic, Population-Based Analytical Methods and Models

    The following material is based on a lecture prepared by Prof. Joe Eisenberg, formerly of the University of California-Berkeley and now at the University of Michigan

    Used with his permission


    Overview l.jpg
    Overview Pathogens:

    • Role of water in disease burden

      • Water as a route of disease transmission

    • Methods of risk estimation

      • Direct: intervention trials

      • Indirect: risk assessment

    • Population-level risks

      • Example: the Milwaukee outbreak


    Importance of waterborne pathogens l.jpg
    Importance of Waterborne Pathogens Pathogens:

    Domestic: U.S. interest in water quality

    • 1993 Cryptosporidium outbreak

    • Increasing number of disease outbreaks associated with water

    • Congressional mandates for water quality

      • (Safe Drinking Water Act)

    • Emphasis on risk assessment and regulation


    Pathways of transmission l.jpg
    Pathways of Transmission Pathogens:

    • Person-person

      • Mediated through fomites (e.g., phone, sink, etc.)

      • Often associated with hygiene practices

    • Person-environment-person

      • Mediated through water, food, or soil

      • Contamination can occur through improper sanitation (example: sewage inflow into drinking water source or lack of latrines)

      • Animals are often sources (Zoonotic pathogens)

      • Exposure can occur through improper treatment of food or water


    The disease transmission process l.jpg
    The Disease Transmission Process Pathogens:

    Risk estimation depends on transmission dynamics and exposure pathways

    Transport to other water sources

    Agricultural

    Runoff

    Drinking

    Water

    Recreational Waters

    or

    Wastewater reuse

    Animals

    Trans.

    Food


    Approaches to risk estimation l.jpg
    Approaches to Risk Estimation Pathogens:

    • Direct approach: The intervention trial

      • Can be used to assess risk from drinking water and recreational water exposures

      • Problems with sensitivity (sample size issue)

      • Trials are expensive

        • less so in developing world settings

    • Indirect approach: Mathematical models

      • Must account for properties of infectious disease processes

      • Pathogen specific models

      • Uncertainty and variability may make interpretation difficult.


    Approaches to risk estimation32 l.jpg
    Approaches to Risk Estimation Pathogens:

    • Combining direct and indirect approaches

      • Models can define the issues and help design studies.

      • Epidemiology can confirm current model structure and provide insight into how to improve the model


    Approaches for risk estimation direct estimates of waterborne infectious illnesses l.jpg
    Approaches for Risk Estimation: Pathogens: Direct estimates of waterborne infectious illnesses

    • Surveillance: count waterborne infectious illnesses

      • How can a waterborne disease outbreak be distinguished from other outbreak causes (food, fomites, etc.)?

      • What about endemic disease?

    • Observational

      • Ecologic studies (e.g., sero-survey comparing communities with and without filtration)

      • Time series (e.g., correlation between turbidity and hospitalization data)


    Approaches for risk estimation distinguishing waterborne gi disease from other gi diseases l.jpg
    Approaches for Risk Estimation Pathogens: :Distinguishing waterborne GI disease from other GI diseases

    • Methods for addressing the question

      • In a single community: a randomized, blinded, placebo-controlled trial

      • design provides an estimate of the effectiveness of a drinking water intervention.

    • Basic study design: two groups

      • “Exposed” group = normal tap water.

      • “Treated” group = use a water treatment device to provide water as pathogen-free as technically possible


    Approaches for risk estimation a tap water intervention trial l.jpg
    Approaches for Risk Estimation Pathogens: : A Tap Water Intervention Trial

    • Enroll 1000 subjects

    • 500 receive an active home water treatment device (and carry drinking water to work, etc. when practical)

    • 500 receive a “placebo” home water drinking device (does nothing to change the water)

    • Follow the subjects for one year with daily logs of GI illness

    • Alternative design: Each household changes device type after 6 months.


    Approaches for risk estimation a tap water intervention trial36 l.jpg
    Approaches for Risk Estimation: Pathogens: A Tap Water Intervention Trial

    • Placebo (control) group (tap water):

      • 90 illnesses over course of the study

      • “Rate” = 90 / 500

        Rate in placebo group = 0.18 per person per year

    • Treated (intervention) group (active device):

      • 60 illnesses in the treated group (active device)

      • “Rate” = 60 / 500

        Rate in treated group = 0.12 per person per year


    Approaches for risk estimation epidemiologic measures l.jpg
    Approaches for Risk Estimation: Pathogens: Epidemiologic Measures

    • Relative Risk (RR)

      Incidence in exposed group

      Incidence in unexposed group

    • Interpretation: the risk of disease in the tap water group is 1.5 times higher than that of the treated group


    Approaches for risk estimation epidemiologic measures38 l.jpg
    Approaches for Risk Estimation: Pathogens: Epidemiologic Measures

    • Attributable Risk (AR)

      Incidence in exposed – Incidence in unexposed

      Interpretation: There are 6 excess cases of disease per 100 subjects receiving tap water


    Approaches for risk estimation epidemiologic measures39 l.jpg
    Approaches for Risk Estimation: Pathogens: Epidemiologic Measures

    • Attributable Risk Percent (AR%)

      Excess cases in exposed

      Incidence in exposed

      Interpretation: 33% of the cases of disease in the tap water group are due to water


    Approaches for risk estimation epidemiologic measures40 l.jpg
    Approaches for Risk Estimation: Epidemiologic Measures Pathogens:

    • To generalize beyond the cohort, need an estimate of the community incidence.

    • PAR: population attributable risk

    • PAR%: population attributable risk %

    • AR compares completely protected group with completely unprotected group.

    • PAR incorporates intermediate exposure


    Approaches for risk estimation epidemiologic measures41 l.jpg
    Approaches for Risk Estimation: Epidemiologic Measures Pathogens:

    • Population attributable risk

    • Incidence in the community–incidence in the unexposed

      Interpretation: In the community, 2 excess cases of disease per every 100 subjects in the community


    Approaches for risk estimation epidemiologic measures42 l.jpg
    Approaches for Risk Estimation: Epidemiologic Measures Pathogens:

    • Population attributable risk percentage

      Excess cases in the community

      Incidence in the exposed

      Interpretation: 14% of the cases of disease in the community are due to tap water


    Approaches for risk estimation tap water intervention trials developed world l.jpg
    Approaches for Risk Estimation: Pathogens: Tap Water Intervention Trials: Developed World

    Trials in immunocompetent populations

    • Canada (Payment)--challenged surface water

      • AR = 0.35 (Study 1), 0.14-0.4 (Study 2)

    • Australia (Fairley)--pristine surface water

      • No effect

    • Walnut Creek (UCB) – pilot trial

      • AR = 0.24 (non-significant effect)

    • Iowa (UCB)--challenged surface water

      • No effect

        Trials in sensitive populations

    • HIV+ in San Francisco (UCB)--mixed sources

    • Elderly in Sonoma (UCB)--intermediate quality surface


    Approaches for risk estimation tap water intervention trials l.jpg
    Approaches for Risk Estimation: Pathogens: Tap Water Intervention Trials

    • Davenport, Iowa study

      • Comparing sham vs. active groups

      • AR = - 365 cases/10,000/year (CI: -2555, 1825)

      • Interpretation: No evidence of a significantly elevated drinking water risk

      • Is the drinking water safe?


    Approaches for risk estimation risk assessment vs intervention trial l.jpg
    Approaches for Risk Estimation: Pathogens: Risk Assessment vs. Intervention Trial

    Comparing estimates from a risk assessment to randomized trial results (Eienberg et al. AJE, submitted)

    • Data collected during the intervention trial

      • Self-report illnesses from participants: Weekly diaries

      • Source water quality: Cryptosporidium, Giardia, enteric viruses

      • Drinking water patterns: RDD survey

      • Water treatment: B. subtilis, somatic coliphage


    Slide46 l.jpg

    Approaches for Risk Estimation: Pathogens: Risk Assessment Model



    Approaches for risk estimation risk assessment results l.jpg
    Approaches for Risk Estimation: Risk Assessment Results Pathogens:

    Overall risk estimate: 14 cases/10,000/yr


    Approaches for risk estimation comparison conclusions l.jpg
    Approaches for Risk Estimation: Comparison/Conclusions Pathogens:

    Table 3. Comparison of risk assessment and intervention trials


    Conclusions l.jpg
    Conclusions Pathogens:

    Risk assessments should use models that can integrate relevant information

    • Health data

      • Epidemiology

      • Basic biology

    • Environmental data

      • Water quality

      • Fate and transport

    • Need a population perspective

      • Model-based approach


    ad