Unit 1: Food Inspection Topic: Investigation of FBD outbreak

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• Unit 1 Food InspectionTopic Investigation of
  FBD outbreak
• Lecture 5

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Objectives

• At the end of the session, students should be
  able to
• Accurately define terms related to FBD
  investigation
• Explain correctly the epidemiological triad,
  using a diagram
• Differentiate between direct and indirect disease
  transmission using examples
• Explain clearly the value of understanding
  incubation periods in respect of investigating
  diseases
• Differentiate correctly among point source,
  propagated source and continuous exposure using
  epi-curves
• Outline clearly the rationale for investigating
  outbreaks
• List the steps involved in the investigation of
  FBDs, based on CDC protocol
• Explain clearly the steps involved in the
  investigation of FBD outbreaks

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Outline

• Concepts in Infectious Disease Epidemiology
• Infectious disease
• Epidemiological Triad
• Disease risk factors
• Disease transmission
• Direct Indirect
• Incubation period
• Endemic, epidemic, pandemic
• Point source vs propagated spread
• Outbreak Investigation Steps
• FB outbreak

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Infectious Disease

• An illness due to a specific infectious agent or
  its toxic products that arises through
  transmission of that agent or its products from
  an infected person, animal or inanimate reservoir
  to a susceptible host either directly or
  indirectly through an intermediate plant or
  animal host, vector or the inanimate environment.
• (Communicable Disease)
• Source Heymann David L. Control of Communicable
  Diseases Manual. Ninetenth Edition, 2008.

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Dynamics of Disease Transmission
Host
Epidemiologic Triad
vector
Agent
Environment

• Human disease results from interaction between
  the host, agent and the environment. A vector
  may be involved in transmission.
• Host susceptibility to the agent is determined by
  a variety of factors, including
• - Genetic background
• - Nutritional status
• - Vaccination
• Prior exposure
• Immune system

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Modes of Disease Transmission

• The potential for a given agent to cause an
  outbreak depends on the characteristics of the
  agent, including the mode of transmission of the
  agent
• Two basic modes of transmission
• Direct
• Indirect
• Diseases can be transmitted directly or indirectly

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Direct Mode of Disease Transmission

• In an infectious setting, immediate and direct
  transfer of an agent to a host by an infected
  person or animal
• Touching, biting, or sexual intercourse are
  classic examples
• Measles virus airborne by droplet spread or
  direct contact with nasal/throat secretions of
  infected persons
• In a noninfectious setting, the host may have
  direct contact with the agent in the environment
• Children ingesting lead paint from playground
  equipment

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Indirect Mode of Disease Transmission

• Vehicle-borne
• Transmission through contaminated inanimate
  objects (toys, food, water, surgical utensils, or
  biological products such as blood, tissues or
  organs)
• Vector-borne
• Transmission by animal
• Mechanical transmission
• Biological transmission
• Airborne
• Transmission occurs when microbial, particulate,
  or chemical agents are aerosolized and remain
  suspended in air for long periods of time

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Incubation Period

• Interval from receipt of infection to the time of
  onset of clinical illness (signs symptoms)
• Different diseases have different incubation
  periods
• No precise incubation period
• A range is characteristic for a disease
• What accounts for this delay?
• Time needed for the pathogen to replicate to the
  critical mass necessary for clinical disease
• Site in the body at which the pathogen replicates
• Dose of the infectious agent received at time of
  infection

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Outcomes of Exposure to an Agent
The spectrum of severity varies by disease 1.
Exposure, No infection 2. Carrier - Individual
harbors the pathogen but does not show evidence
of clinical illness a potential source of
infection (can transmit the agent) 3.
Subclinical Infection - Disease that is not
clinically apparent leads to immunity,
carrier, or non-immunity 4. Clinical
Infection - Apparent disease characterized by
signs and symptoms results in immunity,
carrier, non-immunity, or severe consequences
such as death
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Endemic Epidemic

• Endemic
• The habitual presence (or usual occurrence) of a
  disease within a given geographic area
• Epidemic
• The occurrence of an infectious disease clearly
  in excess of normal expectancy, and generated
  from a common or propagated source

Number of Cases of Disease
Endemic
Epidemic
Time
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Pandemic

• A worldwide epidemic affecting an exceptionally
  high proportion of the global population

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Disease Outbreaks

• Typically, sudden and rapid increase in the
  number of cases of a disease in a population
• Common Source
• Cases are limited to those who share a common
  exposure
• Foodborne, water

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Point Source
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Point source vs Propagated

• Propagated
• Disease often passed from one individual to
  another
• Measles, STDs

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FBD investigation

• The purpose of the investigation are to stop the
  outbreak and prevent further exposures by
• Identifying illnesses associated with the
  incident and verifying that the causative agent
  is food borne
• Detecting all cases, the causative agent, the
  implicated food(s), and the place(s) where the
  food was contaminated or mishandled
• Determining the source and mode of contamination,
  processes or practices associated
• Educating stakeholders prevention
• Determining if the outbreak is part of a larger
  out break

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Foodborne Surveillance System

• Systematically collect data pertaining to FBIs
• Investigation protocol
• Analysis and interpretation of surveillance and
  investigation data
• Disseminate consolidated information to
  appropriate agencies/partners

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Essential Steps in an Outbreak Investigation
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Steps of an Outbreak Investigation

1) Assembly Team 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 person, place and
time 6) Develop hypotheses 7) Evaluate
hypotheses 8) Refine hypotheses and carry out
additional studies 9) Implement control and
prevention measures 10) Communicate findings
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Establish Team

• Epidemiologists, PHIs, Microbiologist, PHNs, RNs,
  physicians, Communication Specialist, Medical
  Technologists etc.
• Free flow of information and coordination
  critical
• Train staff interest, education, ability
• Outbreak kit/supplies
• Forms, equipment, reference library

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Step 1 Establish the existence of an outbreak

• Before you decide whether an outbreak exists, you
  must first determine the expected or usual number
  of cases for the given area and time

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How do we know when we have an excess over what
is expected?
Public Health Surveillance The ongoing and
systematic collection, analysis, and
interpretation of outcome-specific data for use
in the planning, implementation, and evaluation
of public health practice. (Thacker, Berkleman.
Epidemiologic Reviews 198810164-90)
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Notifiable Disease

• Disease for which regular, frequent, and timely
  information regarding individual cases is
  considered necessary for the prevention and
  control of disease

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Step 1 Establish the existence of an outbreak

• Data Sources
• Health department surveillance records for a
  notifiable disease
• Sources such as hospital discharge records,
  mortality records
• Physician based reporting
• Laboratory based reporting
• Public complaints
• School illness/absentee records
• Absentee records from employers
• Sales on anti-diarrheal drugs

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Step 1 Establish the existence of an outbreak

• Two or more person with same disease
• Have similar clinical features/same pathogen
• Time, place, person association
• Single case of botulism, paralytic shell fish
  poisoning or rare disease vibrio vulnificus

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Step 1 Establish the existence of an outbreak

• Whether or not an outbreak is investigated or
  control measures are implemented is not strictly
  tied to verifying that an epidemic exists
• Other factors may come into play, including
• Severity of the illness
• Potential for spread
• Political considerations
• Public concern and pressure from community
• Availability of resources

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Step 2 Verify the diagnosis

• Two goals in verifying a diagnosis
• 1. Ensure that the problem has been properly
  diagnosed -- the outbreak really is what it has
  been reported to be
• Review clinical findings and laboratory results
  for affected people
• Visit or talk to several of the people who became
  ill
• Collect food samples
• 2. For outbreaks involving infectious or toxic
  chemical agents, be certain that the increase in
  diagnosed cases is not the result of a mistake in
  the laboratory.

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Step 3 Define and identify cases

• The first cases to be recognized are usually only
  a small proportion of the total number
• To identify other cases, use as many sources
  possible
• Passive Surveillance - Relies on routine
  notifications by healthcare personnel (recall
  Notifiable Diseases)
• Active Surveillance - Involves regular outreach
  to potential reporters to stimulate reporting of
  specific conditions investigators are sent to
  the afflicted area to collect more information
• Contact physician offices, hospitals, schools to
  find persons with similar symptoms or illnesses
• Send out a letter, telephone or visit the
  facilities to collect information

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Step 3 Define and Identify cases

• Discussion with health workers
• Review case history form
• Collect data from cases (non- cases)
• Be mindful of cultural/language barrier
• Be professional
• Exhibit genuine concern for interviewee
• Parental consent must be obtained before
  interviewing children
• Ask open ended questions first
• Use menu to jag memory
• Obtain specimen
• Line listing

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Step 3 Define and identify cases

• The following information should be collected
  from every affected person in an outbreak
• 1) Identifying information - name, address,
  phone
• 2) Demographic information - e.g., age, sex,
  race, occupation
• 3) Risk factor information
• 4) Clinical information
• Verify the case definition has been met for every
  case
• Date of onset of clinical symptoms to create an
  epidemic curve

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Step 3 Define and identify cases

• Establish a case definition - a standard set of
  criteria for deciding whether a person should be
  classified as having the illness under study
• In many outbreaks, a working definition of the
  disease syndrome must be drawn up that will
  permit the identification and reporting of cases
• As the investigation proceeds and the source,
  mode of transmission and/or etiologic agent
  becomes better known, you can modify the working
  definition
• Primarily used to classify exposed persons as
  cases or non-cases

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Step 3 Define and identify cases

• A case definition includes four components
• Clinical information about the disease,
• Characteristics about the people who are affected
  (person)
• Information about the location (place), and
• A specification of time during which the outbreak
  occurred (time)

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Can you formulate a case definition?
Component Question Asked Factual Item
1. Clinical criteria 2. Time 3. Place 4. Person What were the predominant symptoms? When did infection occur? Where did infection occur? Who may have been affected? Acute onset of gastroenteritis Saturday evening Wedding reception Wedding attendee
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Case Definition

• All students who consumed food at UTechs Canteen
  - Slipe Pen Road on 01/10/12 and who exhibited
  sign/symptoms of vomiting, diarrhoea and
  abdominal cramps.
• As scope broadens, may modify/alter definitions

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Step 3 Define and identify cases

• To increase sensitivity specificity of
  reporting, we use three classifications of cases
  that reflect the degree of certainty regarding
  diagnosis
• 1) Confirmed
• 2) Probable
• 3) Possible
• The case definition is used to actively search
  for more cases beyond the early cases and the
  ones that presented themselves.

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Step 4 Describe and orient the data in terms of
time, place and person

• Characterizing an outbreak by time, place and
  person is called descriptive epidemiology.
• Descriptive epidemiology is important because
• You can learn what information is reliable and
  informative (e.g., similar exposures)
• And what may not be as reliable (e.g., many
  missing responses to a particular question)
• Provides a comprehensive description of an
  outbreak by showing its trend over time, its
  geographic extent (place) and the populations
  (people) affected by the disease

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Step 4 Describe and orient the data in terms of
time

• The time course of an epidemic is shown by the
  distribution of the times of onset of the
  disease, called the Epidemic Curve.
• Graph of the number of cases of the health event
  by their date of onset
• Provides a simple visual display of the
  magnitude and time trend of the outbreak
• May stratify epidemic curves by place
• residence, work, school
• May stratify epidemic curves by personal traits
• age, gender, race
• to assess whether time of onset varies in
  relation to place or person characteristics

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Example of Epidemic Curves
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Step 4 Describe and orient the data in terms of
place

• Assessment of the outbreak by place provides
• Information on the geographic extent of the
  problem
• A spot map indicating place of occurrence of
  cases may show clusters or patterns that provide
  clues to the nature and source of the outbreak
• Patterns reflecting water supply, wind currents,
  or proximity to a restaurant, swimming pool,
  school room or workplace
• If the size of overall population varies between
  comparison areas, a spot map of the area may be
  misleading because it only shows number of cases

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Step 4 Describe and orient the data in terms of
person

• Examine risks in subgroups of the affected
  population according to personal characteristics,
  as well as interaction between characteristics
• - Age, race, sex, occupation, social group,
  medical status
• Characterizing an outbreak by person helps to
  determine which subgroups of the population are
  at risk

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Step 5 Develop hypotheses

• Though we generate hypotheses from the beginning
  of the outbreak, at this point, the hypotheses
  are sharpened and more accurately focused
• Use existing knowledge (if any) on the disease,
  or find analogies to diseases of known etiology
• Hypotheses should address
• Most likely agent/illness
• Most likely vehicle
• Mode of transmission/exposure
• and should be proposed in a way that can be
  tested

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Step 6 Evaluate hypotheses

• Generally, after a hypothesis is formulated, one
  should be able to show that
• 1) all additional cases, lab data, and
  epidemiologic evidence are consistent with the
  initial hypothesis and
• 2) no other hypothesis fits the data as well
• Observations that add weight to validity
• The greater the degree of exposure (or higher
  dosage of the pathogen), the higher the incidence
  of disease
• Higher incidence of disease in the presence of
  one risk factor relative to another factor

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Step 6 Evaluate hypothesis

• Attack rates
• Specific food attack rates
• Cohort Studies - RR
• Case Control Studies -OR
• Next practical

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Step 7 Refine hypotheses and carry out
additional studies

• Additional epidemiologic studies
• What questions remain unanswered about the
  disease?
• What kind of study used in a particular setting
  would answer these questions?
• When analytic studies do not confirm the
  hypotheses
• reconsider the original hypotheses
• look for new vehicles or modes of transmission

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Step 7 Refine hypotheses and carry out
additional studies

• Laboratory and environmental studies
• Epidemiologic studies can
• Implicate the source of infection, and
• Guide appropriate public health action
• Environmental studies often help explain why an
  outbreak occurred and is important
• But sometimes laboratory evidence important _PCR

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Step 8 Implementing control and prevention
measures

• The practical objectives of an epidemic
  investigation are to
• Stop the current epidemic, and
• Establish measures that would prevent similar
  outbreaks in the future.
• Preliminary control measures should be done as
  soon as possible!

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Elements of Epidemic Control
The elements of epidemic control include 1.
Controlling the source of the pathogen (if
known) Remove or inactivate the pathogen 2.
Interrupting the transmission Sterilize
environmental source of spread vector
control 3. Controlling or modifying the host
response to exposure Immunize the
susceptibles use prophylactic
chemotherapy
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Step 9 Communicate the findings

• At the end of the investigation, communicate
  findings to others who need to know
• Prepare a final report
• Provide information on the nature, spread, and
  control measures employed
• The report can take several forms
• 1) An oral briefing for local health authorities
• 2) A written report to a journal
• 3) Formal presentation of recommendations (a
  blueprint for action)

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Conclusion

• 1 ) Assembly Team
• 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
  person, place and time
• 6) Develop hypotheses
• 7) Evaluate hypotheses
• 8) Refine hypotheses and carry out additional
  studies
• 9) Implement control and prevention measures
• 10) Communicate findings