1. Unit 1: Food Inspection Topic: Investigation of FBD outbreak Lecture 5

2. 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

3. 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

4. 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.

5. Dynamics of Disease Transmission
Host
AGENT
HOST
VECTOR
ENVIRONMENT
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

6. 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
Includes virulence - the degree of pathogenicity of a microorganism as indicated by the severity of disease produced and the ability to invade the tissues of the host; by extension, the competence of any infectious agent to produce pathologic effects /includes pathogenicity
Good example: cholera
(1) ingestion of contaminated food/water
(2) feces or vomit of infected persons

7. 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
Measles: one of the most highly communicable diseases; toxoplasmosis by touching cat litter
Droplet ~3 feet

8. 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

9. 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
Sign – what you see; symptom what you feel. A critical variable in investigating an outbreak or epidemic

10. 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
Sub clinical – asymptomatic – infected but do not have an infectious disease example vaccination; some instances the incubation period longer than infectious period, therefore by the time you realize you are sick, you would have been spreading organism (M. Faciparum)

11. 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

12. Pandemic
A worldwide epidemic affecting an exceptionally high proportion of the global population

13. 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

14. Point Source
An epi curve depicts time distribution of onset of initial symptoms for all cases associated with the outbreak – this curve helps to determine whether or not there was a common source vehicle or there was person to person spread. Range of curve equal to approximately 1 incubation period

15. Point source vs Propagated
Disease often passed from one individual to another
Measles, STDs
Slow progressive rise, curve equivalent to several incubation period… might indicate secondary spread or continuous exposure

16. 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
Once the responsible food is identified, effort can be made to recall, stop sale, distribution, service, quarantining, reprocessing, disposing foods

17. 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

18. Essential Steps in an Outbreak Investigation

19. 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
These are the 10 basic tasks involved in an acute disease outbreak setting, presented in logical order.
However, depending on the circumstances, you may be performing several of these tasks simultaneously or in different order during the course of the investigation

20. 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

21. 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

22. 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 1988;10:164-90)

23. Notifiable Disease
Disease for which regular, frequent, and timely information regarding individual cases is considered necessary for the prevention and control of disease
Newly-emerged pathogen (add to list)
Declining incidence (remove from list)

24. 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

25. 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

26. 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

27. 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.

28. 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

29. 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
Before medication – is so find of the types and duration; control specimen as well

30. 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

31. 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

32. 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)

33. 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

34. Case Definition
All students who consumed food at UTech’s 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
As scope is broaden, may modify/ alter definitions – diarrhea, fever

35. 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.
Confirmed
Presumptive
Suspected
Laboratory
Verification
Clinical
Features + ++
To read definitions

36. Descriptive epidemiology is important because:
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
Point source, non point source, continuous exposure; gender; profession; type of restaurant

37. 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

38. Example of Epidemic Curves

39. 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

40. 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

41. 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
The food borne illness is caused by sandwiches consumed by students contaminated by Staphylococcus aureus introduced to sandwiches due to poor worker hygiene during preparation. The illness was caused by consuming fried rice intoxicated with bacillus cererus toxin, which was allowed to be produced based on time temperature abuse of the item

42. 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
People who ate, should be sick. People who ate most should be sick
If chicken and bread- more people who ate chicken should be sick

43. Step 6: Evaluate hypothesis
Attack rates
Specific food attack rates
Cohort Studies - RR
Case Control Studies -OR
Next practical

44. 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

45. 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

46. 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!
The underlying purposes of all epidemic investigations are to control and/or prevent further disease.
So, even though this is listed as Step 9,

47. 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

48. 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)
as a point of reference for similar outbreaks in the future

49. 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