1. Outbreak Investigation
Dr Tauseef Ismail

2. Outbreak
A sudden increase in the number of individuals who contact a specific infectious disease in a population, putting others at risk. OR
Spread of disease, which occurs in a short period of time and in a limited geographic location (i.e, neighborhood, community, school, or hospital)

3. Outbreak Investigations
Three critical variables in investigating an outbreak or epidemic are:
When did the exposure take place?
When did the disease begin?
What was the incubation period for the disease?

4. Steps of an Outbreak Investigation

5. Steps of an Outbreak Investigation
Preparation
Confirm the existence of outbreak
Verify the diagnosis
Establish a case definition
Find cases systematically & record information
Perform descriptive epidemiology
Develop hypotheses
Evaluate hypotheses epidemiologically
As necessary, reconsider, refine, and re-evaluate hypotheses.
Implement control and prevention measures
Communicate findings

6. 1. Preparation Scientific knowledge Supplies Equipment Investigation
Review literature
Consult experts
Sample questionnaires
Supplies
Consult with laboratory
Equipment
Laptop, camera etc.
As a field investigator, you must have the appropriate scientific knowledge, supplies, and equipment to carry out the investigation before departing for the field. Discuss the situation with someone knowledgeable about the disease and about field investigations, and review the applicable literature. In previous similar outbreaks, what have been the sources, modes of transmission, and risk factors for the disease? Assemble useful references such as journal articles and sample questionnaires.
Before leaving for a field investigation, consult laboratory staff to ensure that you take the proper laboratory material and know the proper collection, storage, and transportation techniques. By talking with the laboratory staff you are also informing them about the outbreak, and they can anticipate what type of laboratory resources will be needed.
You also need to know what supplies or equipment to bring to protect yourself. Some outbreak investigations require no special equipment while an investigation of SARS or Ebola hemorrhagic fever may require personal protective equipment such as masks, gowns, and gloves.

7. 2. Establish existence of an outbreak
Is an outbreak truly occurred?
through surveillance records for notifiable diseases.
hospital data.
data from other facilities
community survey.

8. 3. Verify the Diagnosis
Ensure proper diagnosis and rule out lab error as the bias for increased diagnosis
Review clinical findings, lab results

9. Verify the Diagnosis cont.
See and talk with patients if at all possible
Better understand clinical features
Gather critical information
Source of exposure
What they think caused illness
Knowledge of others with similar illness
Helpful in generating ideas for hypothesis about etiology and spread

10. 4. Establish a case definition
Includes clinical criteria and restrictions by time, place and person
Classification
Definite (confirmed)
Laboratory confirmed
Probable
Typical clinical features without lab confirmation
Possible (suspected)
Fewer of the typical clinical features
A case definition is a standard set of criteria for deciding whether an individual should be classified as having the health condition of interest. A case definition includes clinical criteria and — particularly in the setting of an outbreak investigation — restrictions by time, place, and person. The clinical criteria should be based on simple and objective measures such as "fever ≥ 40°C (101°F)," "three or more loose bowel movements per day," or "myalgias (muscle pain) severe enough to limit the patient's usual activities. " The case definition may be restricted by time (for example, to persons with onset of illness within the past 2 months), by place (for example, to residents of the nine-county area or to employees of a particular plant) and by person (for example, to persons with no previous history of a positive tuberculin skin test, or to premenopausal women). Whatever the criteria, they must be applied consistently to all persons under investigation.

11. Meningococcal Disease — PAHO (Pan American Health Organization) Case Definition
Clinical case definition
An illness with sudden onset of fever (>38.5°C rectal or >38.0°C axillary) and one or more of the following: neck stiffness, altered consciousness, other meningeal sign or petechial or puerperal rash.
Laboratory criteria for diagnosis
Positive cerebrospinal fluid (CSF) antigen detection or positive culture.

12. Case classification
Suspected: A case that meets the clinical case definition.
Probable: A suspected case as defined above and turbid CSF (with or without positive Gram stain) or ongoing epidemic and epidemiological link to a confirmed case.
Confirmed: A suspected or probable case with laboratory confirmation.

13. Example: Case Definition for Hepatitis A
Confirmed case:
– Anti-HAV IgM+
Probable case:
Pale skin
Suspect case:
Any two of the following:
Abdominal pain, fever, nausea, anorexia, malaise

14. 5. Find cases systematically & record information
Target health care facilities where diagnosis is likely to be made
Enhanced passive surveillance e.g. letter describing situation and asking for reports.
Active surveillance e.g. phone or visit facility to collect information
Alerting the public
Media alert to avoid contaminated food products and seek medical attention if symptoms arise.

15. 5. Find cases systematically & record information contd….
Identifying information
Name, address, and telephone number is essential if need to contact patients additional questions.
Also to Notify them of lab results and outcomes of investigation
Names also helps in checking for duplicate records while addresses allow for Mapping the geographic extent.
Demographic information.
Provide “person” characteristics for defining population at risk

16. 5. Find cases systematically & record information contd….
Clinical findings
Signs and symptoms allow to Verify that the case definition has been met
Date of onset is needed to Chart the time course of outbreak.
Reporter information
Id of person making report

17. 5. Find cases systematically & record information contd….
Line listing
Abstraction of selected critical items from above information

18. What is a Line Listing? A rectangular database similar to spreadsheet
Provides summary of key data about cases in an outbreak
Each row represents one case
Each column represents one variable
First column usually identifier —name, initials, or ID number
Can be paper or electronic
Can be quickly reviewed and updated

19. Example of a Line Listing

20. 6. Perform Descriptive Epidemiology
After collection of data characterize the outbreak by:
Time
Place
Person

21. Time (Epidemic curve) Epidemic curve
Histogram of the number of cases by their date of onset
Visual display of the outbreak’s magnitude and time trend
Common source vs. Propagated

22. Graphical Representation of an Outbreak
Classic epi. curve

23. Place (spot map, shaded map)
Geographic extent of problem
Clusters or patterns providing important etiologic clues
Spot maps
Where cases live, work or may have been exposed

24. Person (Tables) Determine what population at risk
Usually define population by host characteristics or exposure
Use rates to identify high-risk groups
Numerator = number of cases
Denominator = number of people at risk

25. 7. Develop Hypotheses Source of the agent Mode of transmission
Hypotheses should address
Source of the agent
Mode of transmission
Vector or vehicle
Exposure that caused disease

26. Develop Hypotheses Generating the hypothesis
Talk to several case-patients
Use open ended questions
Ask lots of questions
Talk to local health department staff

27. 8. Test Hypotheses
Evaluate the credibility of your hypotheses in one of two ways;
Compare with established facts
When clinical, lab, environmental and/or epi data undoubtedly support hypothesis
Use analytic epidemiology to quantify relationships
Cohort studies
Case control studies

28. 9. Refine hypotheses and do additional studies
Epidemiologic
When analytical epi unrevealing need to reconsider your hypotheses
Go back and gather more information
Conduct different studies
Laboratory
Additional tests

29. 10. Implement Control /Prevention Measures
Implement control measures as soon as possible
May be aimed at agent, source, or reservoir
eliminate the source
interrupt transmission
reduce susceptibility
Create mechanism to evaluate both short and long-term effectiveness of control / prevention measures

30. 11. Communicate Findings Oral briefing for local authorities
Local health authorities and persons responsible for implementation of control and prevention measures
Written reports;
that follows intro, background, methods, results, discussion and recommendations.

31. Communicate the Findings

32. References