Fundamentals of Epidemiology and Outbreak Investigations

1
Fundamentals of Epidemiology andOutbreak
Investigations
Version 2 February 2006
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Fundamentals of Epidemiology andOutbreak
Investigations

• Developed by
• Connecticut Partnership for Public Health
  Workforce Development
• Yale University School of Public Health
• Adapted for distribution by
• Yale Center for Public Health Preparedness

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Fundamentals of Epidemiology andOutbreak
Investigations

• Course content source
• US Department of Health and Human Services,
  Centers for Disease Control and Prevention
• http//www.cdc.gov/excite/index.htm

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Fundamentals of Epidemiology andOutbreak
Investigations

• Funded by
• Connecticut Department of Public Health
• Centers for Disease Control and Prevention Public
  Health Preparedness and Response for Bioterrorism
  Cooperative Agreement
• Centers for Disease Control and Prevention Center
  for Public Health Preparedness Cooperative
  Agreement
• New England Alliance for Public Health Workforce
  Development Health Resources and Services
  Administration Grant No. D20HP00003

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Training Schedule

• Welcome and Housekeeping Items
• Pre-Test
• Purpose and Learning Objectives
• Lecture
• Epidemiology Fundamentals
• Outbreak Investigations
• Group Exercise
• Post-Test

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Purpose of Training

• To provide a quick refresher on
• Basic epidemiology
• Steps in outbreak investigations

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Learning Objectives

• At the end of todays session, you will be able
  to
• Describe how the sanitarian can work with the
  epidemiologist and other team members in outbreak
  investigations
• List the reasons for and steps in an outbreak
  investigation
• Describe and use some of the basic tools of field
  epidemiology

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Role of Non-Epidemiologists in Outbreak
Investigations

• Assure outbreak comes to attention ASAP of those
  with experience and authority to investigate.
• Report outbreaks to the State DPH.
• Joint investigations by the LHD and DPH.
• Provide assistance, as needed, depending on
  expertise.
• Sanitarians can help to develop questionnaires,
  conduct environmental investigation.
• Surge capacity needed to answer phones/ public
  inquiry conduct interviews for analytic studies

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Roles in Foodborne Outbreak Investigations
Graphic developed by Terry Rabatsky-Ehr, Regional
Epidemiologist, CT DPH
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Fundamentals of Epidemiology andOutbreak
Investigations

• What is Epidemiology?
• Introduction to the Categories of Epidemiology
  and Types of Epidemiological Studies
• Overview of the Disease Transmission Cycle
• Outbreak Investigations Steps and Tools
• But first
• Consider the following three incidents and ask
  What does public health do now?

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Incident 1

• While reviewing surveillance data, a nurse noted
  three cases in a single month of hepatitis B
• Three patients did not seem to have the usual
  risk factors
• All three received injections at the same health
  care facility
• Is this a coincidence?
• Did these three cases occur by chance?
• Is there a link?

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Incident 2

• Nurse reported two cases of severe respiratory
  illness, one of which had been fatal
• Both people had attended the annual American
  Legion Convention
• Between July 26 and August 2, 18 conventioneers
  had died
• Led to the discovery of the gram-negative
  pathogen, Legionnella pneumophila

Fluorescent microscopy of Legionella pneumophilia
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Incident 3

• Physician reports three patients with a marked
  increase in their white blood cell count and
  severe muscle pain
• All had taken oral preparations of L-tryptophan
• New syndrome identified EMS
• Problem traced to a contaminant introduced in the
  production process at a single facility

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Summary

• What do these three incidents have in common?
• They were unexpected.
• They demanded a response.
• The investigators had to go out into the field to
  solve the problem.
• They illustrate some of the key reasons for
  needing applied, or field, epidemiology

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I. What is Epidemiology?

• The study of the distribution and determinants
  of health-related states in specified
  populations, and the application of this study to
  control health problems."
• The following key words will be defined
• - Study - Distribution
• - Determinants - Health-related states
• - Population

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Examination of Key Words

• Study Epidemiology is a quantitative discipline
  based on statistics and research methodologies.
• It is the basic science of public health.
• Distribution Epidemiology characterizes disease
  based on person, place and time.
• Determinants Epidemiology looks for causes or
  factors associated with an increased risk of
  disease.

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Examination of Key Words

• Health-related states Epidemiology applies to
  the whole spectrum of health-related events
• Chronic disease, environmental problems,
  behavioral problems, injuries, and infectious
  disease
• Populations Epidemiology deals with groups of
  people rather than with individual patients

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Role of Epidemiology

• Epidemiology is more than just an analytical
  tool for studying diseases and their
  determinants.
• Epidemiologic data
• Steers public health decision making
• Aids in developing and evaluating interventions
  to control and prevent health problems
• Use of epidemiological data to steer decision
  making to control and prevent health problems Is
  the primary function of applied, or field,
  epidemiology

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Comparison Between Healthcare and Public Health
Practice

• Public Health
• Focus population
• Data from surveillance or descriptive studies
• Generate hypothesis
• Analytical studies
• Community intervention

• Healthcare
• Focus one person
• Data from medical history
• Make differential diagnosis
• Diagnostic studies
• Medical treatment

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What Do Epidemiologists Do?

• Count cases of disease or injury
• Define the affected population
• Compute rates of disease or injury in that
  population
• Compare rates with those found in other
  populations
• Make inferences regarding patterns of disease
• Determine whether a problem exists

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II. Types of Epidemiological Studies

• Experimental Epidemiologist controls exposure of
  subjects to an intervention and observes the
  outcome
• Observational Epidemiologist observes exposure
  and outcome without controlling either
• Descriptive Epidemiologist collects information
  to characterize and summarize health event
• Analytical Epidemiologist compares groups to
  identify risk factors

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Types of Epidemiology

• Descriptive epidemiology is concerned with
• Person (who)
• Place (where)
• Time (when)
• Analytical epidemiology uses the information
  gathered during the descriptive process to answer
• How
• Why

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Descriptive Studies Deaths Associated with
Tractor Injuries by Month of Death, Georgia
1971-1981

• What might this data mean?

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Descriptive StudiesDeaths Associated with
Tractor Injuries by Time of Day

• What might this data mean?

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Descriptive StudiesDeaths Associated with
Tractor Injuries by Place
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Descriptive StudiesDeaths Associated with
Tractor Injuries by Age

• What might this data mean?

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Analytic Studies 1 Cross-sectional study

• Basically a survey that takes a snapshot of the
  population.
• Steps
• Define the population to be studied
• Collect information from members of population on
  disease and exposure
• Examine the relationship between disease and
  exposure

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Analytic Studies 2 Cohort study

• Prospective study - follows populations of people
  over time
• Steps
• Select populations that were and were not exposed
  to a hypothesized risk factor
• Follow populations for occurrence of disease
• Compare disease occurrence in those with and
  without exposure at beginning

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Analytic Studies 3 Case-Control Study

• Retrospective study Epidemiologists work
  backward from the case
• Steps
• Select subjects with disease (case) and without
  disease (control)
• Collect information on hypothesized risk factors
• Compare risk factors in cases and controls

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Limit of Analytical Studies

• Analytic studies enable us to quantify
  (mathematically calculate) the relationship
  between an exposure and a health outcome
• However, a mathematical relationship between an
  effect and health outcome is not enough to
  establish causation.

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Cause-and-Effect Relationship

• In general, five criteria must be met to
  establish a cause-and-effect relationship
• Strength of Association clear mathematical
  relationship
• Consistency observation must be repeatable
• Temporality cause must precede effect
• Plausibility must make sense biologically
• Biological Gradient must be dose-response
  relationship

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III. Disease Transmission

• Key terms defined
• Epidemic is the occurrence of more cases than
  would normally be expected in a specific place or
  group over a given period of time
• Outbreak is basically the same thing
• Cluster is a group of cases that may or may not
  represent a greater than expected rate
• Endemic is a persistent level of occurrence of a
  disease
• Pandemic is a very widespread, often global
  epidemic

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Disease Transmission

• For an outbreak, or epidemic, to occur, the basic
  elements of disease causation and an adequate
  chain of transmission must be present.
• Disease occurs when an outside agent capable of
  causing the disease meets a host that is
  vulnerable to the agent in an environment that
  allows the agent and host to interact.
• Then, given a chain of transmission from one host
  to another and a suitable mode of spread, an
  outbreak can develop.

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Key Terms Defined Agent

• Agent is the entity necessary to cause disease in
  a susceptible host
• An agent can be biological, physical, chemical,
  or nutritional
• Agents have important characteristics
• Infectivity capacity to cause infection in host
• Pathogenicity capacity to cause disease in host
• Virulence severity of disease that agent causes

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Key Terms Defined Host

• Host is the person that may be acted upon by the
  agent
• Status of the host is classified as
• susceptible to the agent
• immune to the agent
• infected by the agent
• Hosts response to exposure can show
• no effect
• manifest subclinical disease
• atypical symptoms
• straightforward illness
• severe illness

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Key Terms Defined Environment

• Environment conditions or influences that are
  not part of either the agent or the host, but
  that influence their interaction
• Factors can include
• physical
• climatologic
• biologic
• social
• economic conditions

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Disease Transmission

• Agent, host, and environment alone are not
  sufficient to cause an epidemic
• An adequate chain of transmission must be present
• A chain of transmission requires the following
  elements
• a source of the agent
• a portal of exit from the source
• a mode of transmission
• and a portal of entry into the susceptible person

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Transmission Elements Defined

• Source of infection may be a human, an animal or
  the environment
• Portal of exit is a pathway by which the agent
  can leave the source
• Mode of transmission is the means of carrying
  agent to the host
• Portal of entry is the pathway that gives the
  agent access to tissue where it can multiply or
  act

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Modes of transmission

• Direct
• Direct contact
• Droplet nuclei
• Indirect
• Airborne
• Vehicleborne
• Vectorborne
• Mechanical
• Biologic

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Field Epidemiology

• Field epidemiology is practice or application of
  epidemiology to control and prevent health
  problems
• Act when problem is acute and unexpected and when
  quick action is required
• High levels of community concern
• Involvement of the press
• Political pressure

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Field Epidemiology

• Field investigations are action oriented, with
  the main goal being to solve a pressing public
  health problem
• There is a need to institute the controls
  necessary to safeguard health as soon as possible
• Challenges to investigators
• limited control over the situation
• little time for planning a study
• limited date sources and laboratory samples
• Must do best science possible under the
  circumstances

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IV. Outbreak InvestigationsSteps and Tools
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Challenges in Outbreak Investigations

• Cause, source may not be known
• Large numbers of people may be affected
• Residents fear more illness
• Possible hostility or defensiveness if an
  individual, product or company is accused of
  being the source.
• Epidemiological team must remain calm,
  professional and scientifically objective

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Uncovering Outbreaks

• Call from a doctor, healthcare provider, citizen
• Routine analysis of public health surveillance
  data
• Data on health which are systematically
  collected, analyzed, interpreted, and
  disseminated.
• Data analysis shows an increase over normal
  background level

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Why Investigate Outbreaks?

• Control and prevention
• Severity and risk to others
• Research opportunities
• Training opportunities
• Program considerations
• Public, political, or legal concerns

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Control and Prevention

• Control the outbreak at hand and prevent future
  outbreaks
• Assess its extent and the characteristics of the
  population at risk
• Design measures to prevent additional cases
• Investigate further to identify its source and
  use that information to develop measures that
  will prevent future outbreaks.
• Strike a balance between instituting control
  measures and conducting further investigation.

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Severity and Risk to Others

• It is urgent to investigate an outbreak when the
  disease is severe and could affect more people

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Research Opportunities

• Each outbreak offers a unique opportunity to
  study the natural history of the disease in
  questionincluding the agent, mode of
  transmission, and incubation period.
• Epidemiologists can learn more about the impact
  of control measures and the usefulness of new
  epidemiological and laboratory techniques.

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Training Opportunities

• Investigative skills improve with practice and
  experience.
• Pairing a seasoned epidemiologist with an
  epidemiologist-in-training has value

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Program Considerations

• Investigating an outbreak of a disease targeted
  by public health authorities for prevention and
  control may highlight
• Populations at risk that have been overlooked
• Failures in the programs intervention strategy
• Changes in the agent causing the disease
• Events beyond the scope of the program

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Public, Political, or Legal Considerations

• Public, political, or legal concerns sometimes
  override scientific concerns in the decision to
  conduct an investigation.
• Many health departments have learned that it is
  essential to be "responsibly responsive" to
  public concerns

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10 Steps in an Outbreak Investigation

• 1 Prepare for field work
• 2 Establish the existence of an outbreak
• 3 Verify the diagnosis
• 4 Define and identify cases
• 5 Describe and orient the data in terms of
  time, place, and person
• 6 Develop hypotheses
• 7 Evaluate hypotheses
• 8 Refine hypotheses and carry out additional
  studies
• 9 Implementing control and prevention measures
• 10 Communicate findings

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Step 1. Prepare for Field Work

• Research the disease and gather supplies and
  equipment
• Make necessary administrative and personal
  arrangements for such things as travel, etc.
• Consultations with all parties to determine their
  role in the investigation and who local contacts
  are

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Step 2. Establish Existence of an Outbreak

• Is a suspected outbreak a real outbreak?
• Some are true outbreaks with common cause
• Some are unrelated cases of the same disease
• Others are unrelated cases of similar, but
  unrelated, diseases
• To determine if an outbreak exists (i.e., whether
  the observed number of cases exceeds the expected
  number), first the expected number of cases for
  the area in the given time frame must be
  determined.

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Step 2. Establish Existence of an Outbreak

• Compare current cases with previous occurrences
• Check health department records
• Consult local data sources
• Make estimates from neighboring states or
  national data

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Step 2. Establish Existence of an Outbreak

• If current number of reported cases exceeds
  expected number, further investigation is needed
• Many factors affect changes in total number of
  cases reported
• Change in reporting procedures or case definition
• Increased local interest or public awareness
• Improved diagnostic procedures
• Seasonal population changes

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Step 3. Verify the Diagnosis

• Epidemiologists identify as accurately as
  possible the nature of the disease.
• First, to ensure the problem has been properly
  diagnosed and that it really is what it is
  reported to be.
• Second, for outbreaks involving infectious or
  toxic-chemical agents, to be certain that the
  increase in diagnosed cases is not the result of
  a mistake in the laboratory.

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Step 3. Verify the Diagnosis

• Review clinical findings and laboratory results
  for people affected
• Verify laboratory findings
• Prepare for any specialized laboratory work
• Visit and interview several people who became ill

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Step 4. Define and Identify Cases

• Epidemiologists establish a case definition a
  standard set of criteria for deciding whether a
  person should be classified as having the disease
  or condition under study.
• Usually includes components
• Clinical information about the disease 
• Characteristics about the people who are affected
• Information about the location or place
• A specification of time during which the outbreak
  occurred.

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Step 4. Define and Identify Cases

• Criteria are be based on objective measures that
  are consistently applied without bias to all
  people included in the investigation
• Case definitions are broad enough to include most
  actual cases while avoiding false-positive
  cases (when the case definition is met, but the
  person does not have the disease).

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Step 4. Define and Identify Cases

• Investigators often classify cases as one of the
  following
• Confirmed usually has laboratory verification
• Probable usually has clinical features without
  lab verification
• Possible usually has fewer of typical clinical
  features

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Step 4. Define and Identify Cases

• When an outbreak is first recognized the
  epidemiologist must cast the net wide to
  identify cases
• Possible sources of cases
• Health care facilities
• Public alert
• Survey of population, particularly if outbreak
  occurs in restricted population
• Case patient referral

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Step 4. Define and Identify Cases

• The following information is collected
• Identifying information
• Demographic information
• Details to characterize population at risk
• Clinical information
• Allows the creation of a epidemic curve and a
  description of the spectrum of illness
• Risk factor information
• Helps to tailor investigation to the specific
  disease in question

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Case Report Form

• This information is entered on a case report
  form.
• CT DPH has a number of different case report
  forms, depending on the nature of the outbreak

Sample report form from the DPH Food Protection
Program
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Line Listing

• Next, selected critical items are abstracted into
  a table called a line listing
• Each column represents an important variable,
  such as age and sex
• Each row represents a different case, by number
• This simple format allows the investigator to
  scan key information on every case and update it
  easily

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Example of a Line Listing
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Step 5. Describe and Orient the Data

• Characterize the outbreak by time, place, and
  person (descriptive epidemiology)
• Benefits
• Allows you to become familiar with the data,
  especially what is and is not reliable
• Provides a comprehensive description of the
  outbreak
• Allows you to develop a causal hypothesis based
  on what is known about the disease

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Characterizing By Time Epidemic Curve

• Epidemic curve or epi curve a graph of the
  number of cases by their date of onset.
• Simple visual display of outbreaks magnitude and
  time trend.
• Shows course of epidemic
• May enable estimation of probable time period of
  exposure
• May enable inferences to be drawn about the
  epidemic pattern

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Characterizing By Time Epidemic Curve

• How to draw an epidemic curve
• Know the time of onset for each person
• Number of cases is plotted on y-axis
• Time is plotted on the x-axis
• The unit of time is based on incubation period
  and length of time over which cases are
  distributed. Select a unit that is one-fourth to
  one-third as long as the incubation period.
• Show the pre- and post-epidemic period to
  illustrate the activity during those periods

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Example 1 Epidemic Curve

• Insert EPI Curve

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Example 2 Epidemic Curve
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Epidemic Curve Interpreting the Shape

• Point source epidemic
• Shape a steep up slope, a peak and a gradual
  down-slope
• Interpretation - people are exposed to the same
  source over a relatively brief period
• Continuous common source epidemic
• Shape - curve will have a plateau instead of a
  peak
• Interpretation - people are exposed to the same
  source over an extended period
• Propagated epidemic
• Shape - a series of progressively taller peaks
• Interpretation - person-to-person spread

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Example 1 Epidemic Curve

• Insert EPI Curve

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Example 2 Epidemic Curve
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Characterizing By Time Epidemic Curve

• Outliers cases that stand apart
• Early case may represent
• a background (unrelated) case
• source of epidemic (index case)
• an early exposure
• Late cases may be
• unrelated
• have long incubation periods
• indicate later exposure
• secondary cases

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Example 2 Epidemic Curve
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Characterizing By Place Spot Map

• Assessment of an outbreak by place provides
  information on the geographic extent of a problem
  
• A spot map of cases in a community may show
  clusters or patterns that reflect water supplies,
  wind currents, or proximity to a restaurant or
  grocery store.

John Snow and Broad Street Pump map
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Characterizing By Place Spot Map

• If the size of the overall population varies
  between the areas under comparison, a spot map,
  because it shows numbers of cases, can be
  misleading. This is a weakness of spot maps.
• Discuss the data in the spot map on the right.
  What are some possible interpretations?

Dead crow sightings, 2000 (CT DPH Mosquito
Management Program 2000 Annual Report)
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(No Transcript)
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Characterizing By Place

• To compensate, maps can show the proportion of
  people affected in each area
• This also represents the rate of disease or, in
  the investigation of an outbreak, the "attack
  rate"

Connecticut Epidemiologist, July 2001
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Characterizing By Person

• Determine the populations at risk by
  characterizing the outbreak by person
• Define populations by
• Personal characteristics (Examples age, race,
  sex, or medical status)
• Exposures (Examples occupation, leisure
  activities, use of medications, tobacco, drugs)
• Age and sex are usually assessed first, because
  they are often the characteristics most strongly
  related to exposure and to the risk of disease.

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Step 5. Describe and Orient the Data in Terms of
Time, Place, Person

• Summarize
• After characterizing an outbreak by time, place,
  and person (descriptive epidemiology),
  epidemiologists need to summarize what they know
  to see whether their initial hypotheses are on
  track.
• New hypotheses may need to be developed to
  explain the outbreak.

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Step 6. Develop Hypotheses

• Hypotheses may be based on
• Interviews with affected people
• Consultation with health officials in community
• Descriptive epidemiology - person, place and time
• It should incorporate the known characteristics
  of the agent
• It should be testable.

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Step 7. Evaluate Hypotheses

• Two approaches
• Compare hypotheses with the established facts.
• This method is used when the evidence is so
  strong that the hypothesis does not need to be
  tested
• Use analytic epidemiology to test hypotheses by
  using a comparison group to quantify
  relationships between various exposures and the
  disease.

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Step 7. Evaluate Hypotheses Analytic Studies

• There are two types of analytic studies
• Cohort Studies compare groups of people who
  have been exposed to suspected risk factors with
  groups who have not been exposed.
• Case-Control Studies compare people with a
  disease (case-patients) with a group of people
  without the disease (controls).

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Study Type Cohort Studies

• Best for analyzing an outbreak in a small
  well-defined population
• Example gastroenteritis among people who
  attended a wedding
• Ask each attendee the same set of questions about
  potential exposures
• In cohort studies, an attack rate can be
  calculated for people who ate a particular item
  (were exposed) and an attack rate for those who
  did not eat that item (were not exposed).

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Attack Rates

• For the exposed group, the attack rate equals
  the number of people who ate item and became ill
  divided by () the total number of people who ate
  that item.

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Attack Rates

• For the not exposed group, the attack rate
  equals the number of people who did not eat item
  but still became ill divided by () the total
  number of people who did not eat that item.

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Relative Risk

• To identify source of outbreak, look for
• High attack rate among those exposed and
• Low attack rate among those not exposed and
• In addition
• Most of the people who became ill should have
  consumed the item
• Calculate the relative risk mathematical
  association between exposure and illness for each
  food and beverage

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Relative Risk

• Relative risk is calculated by dividing () the
  attack rate for people who were exposed to the
  item by the attack rate for those who were not
  exposed.

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Attack Rate Table 1
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Example Attack Rates

• Food
• Baked Ham
• Mashed potatoes
• Spinach
• Cabbage salad
• Milk
• Ice Cream (Van)
• Ice Cream (Choc)
• Fruit salad

• Exposed Group
• 29/46 63
• 23/37 62
• 26/43 60
• 18/28 64
• 2/4 50
• 43/54 80
• 25/47 53
• 4/6 67

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Example Attack Rates

• Food
• Baked Ham
• Mashed potatoes
• Spinach
• Cabbage salad
• Milk
• Ice Cream (Van)
• Ice Cream (Choc)
• Fruit salad

• Not Exposed Group
• 17/29 59
• 23/37 62
• 20/32 62
• 28/47 60
• 44/71 62
• 3/21 14
• 20/27 74
• 42/69 61

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Attack Rate Table 2
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Attack Rate Table 3
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Study Type Case Control Studies

• When the population in an outbreak is not well
  defined, a case control study design is used
• Both case-patients and controls are asked about
  their exposures
• Controls must not have the disease, but should be
  from the same population as the case-patients
• The measure of association used is called an odds
  ratio

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Odds Ratio

• In a case-control study, attack rates cannot be
  calculated because the total number of people in
  the community who were and were not exposed to
  the source of the disease under study is not
  known
• An odds ratio is used to measure of association
• To calculate an odds ratio, it is helpful to look
  at data in a 2 x 2 table.

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Odds Ratio

• Example
• Suppose an epidemiologist were investigating an
  outbreak of hepatitis A in a small town.
• The suspected source was a favorite restaurant of
  the townspeople.
• After questioning case-patients and controls
  about whether they had eaten at that restaurant,
  the data might look like this in a 2 x 2 table

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Odds Ratio 2 x 2 Table
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Odds Ratio

• The odds ratio is calculated as ad/bc
• Using the example from previous 2 x 2 Table
• 30 x 70 36 x 10 5.8
• People who ate at restaurant A were 5.8 times
  more likely to develop hepatitis A than were
  people who did not eat there
• Now epidemiologists can compare the odds ratio
  with the odds ratios for other possible sources

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Step 7 Evaluate HypothesesTesting Statistical
Significance

• Determine how likely the study results could have
  occurred by chance
• Called testing for statistical significance
• Steps to testing statistical significance
• State null hypothesis no association between
  exposure and outcome
• Calculate chi-square test
• Look up corresponding p-value in table of
  chi-squares.

102
Interpreting P-Values

• Epidemiologists set in advance a cutoff point
  above which they will consider that chance is a
  factor
• The common cutoff point is .05
• If the p-value is below the cutoff point, the
  finding is considered statistically significant
  and the null hypothesis is rejected
• The smaller the p-value, the stronger the
  evidence is for statistical significance

103
Step 8. Refine Hypotheses and Carry Out
Additional Studies

• When analytic epidemiological studies do not
  confirm the hypotheses, they must be reconsidered
  along with new vehicles or modes of transmission
• Even when an analytic study identifies an
  association, hypotheses will need to be refined
• Often, more specific exposure histories or a more
  specific control group are needed
• Epidemiologists consider what questions remain
  unanswered, and what kind of study might be used
  in the particular setting to answer some of these
  questions

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Step 8. Refine Hypotheses and Carry Out
Additional Studies

• Laboratory and environmental studies
• While epidemiology can implicate vehicles and
  guide appropriate public health action,
  laboratory evidence can clinch the findings
• Environmental studies often help explain why an
  outbreak occurred and may be very important in
  some settings

105
Step 9. Implementing Control and Prevention
Measures

• Control measures, which can be implemented early,
  should be aimed at specific links in the chain of
  infection, the agent, the source, or the
  reservoir
• In some situations, control measures are directed
  at interrupting transmission or exposure
• Limit airborne spread
• Use the method of cohorting by putting infected
  people together in separate area
• Some control measures are directed at reducing
  susceptibility, such as travel immunizations

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Step 10. Communicate Findings

• The final task in an investigation is to
  communicate the findings to others who need to
  know.
• This communication usually takes two forms
• 1) an oral briefing
• 2) a written report

107
Role of Non-Epidemiologists in CT Outbreak
Investigations

• Assure outbreak comes to attention ASAP of those
  with experience and authority to investigate.
• Report outbreaks to the state DPH.
• Joint investigations by the LHD and DPH.
• Provide assistance, as needed, depending on
  expertise.
• Sanitarians can help to develop questionnaires,
  conduct environmental investigation.
• Surge capacity needed to answer phones/public
  inquiry conduct interviews for analytic studies.

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Roles in Foodborne Outbreak Investigations