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1. RESEARCH AND EPIDEMIOLOGY
OUTBREAK INVESTIGATION

2. Objectives
1. Develop a case definition for an outbreak.
2. Prioritize an outbreak for further
investigation
3. Describe the initial steps of an outbreak
investigation including
 Verify the diagnosis
 Search for additional cases
 Create a case definition
 Generate a hypothesis about the source

3. June Course 2006 3

4. DEFINITION
• According to WHO
• A disease outbreak is the occurrence of cases
of disease in excess of what would normally
be expected in a defined community,
geographical area or season. An outbreak may
occur in a restricted geographical area, or may
extend over several countries. It may last for a
few days or weeks, or for several years.

5. Definitions continue
• Also according to CDC:
• A single case of a communicable disease long
absent from a population, or caused by an
agent (e.g. bacterium or virus) not previously
recognized in that community or area, or the
emergence of a previously unknown disease,
may also constitute an outbreak and should
be reported and investigated.

6. Definitions continue
• A disease outbreak happens when a disease
occurs in greater numbers than expected in a
community or region or during a season. An
outbreak may occur in one community or even
extend to several countries. It can last from
days to years.
• Sometimes a single case of a contagious disease
is considered an outbreak. This may be true if it
is an unknown disease, is new to a community,
or has been absent from a population for a long
time.

7. Definitions continue
• If you observe what you think might be a disease
outbreak, report it right away to your health care
provider or public health department.
• If a disease is endemic (habitually present in a
community) it is necessary to estimate its
previous frequency and thereby confirm an
increase in incidence above the normal endemic
level.

8. Definitions continue
• In summary
• An incident in which two or more people
experiencing a similar illness are linked in time
or place
• A greater than expected rate of infection
compared with the usual background rate for
the place and time where the outbreak has
occurred

9. Definitions continue
• A single case for certain rare diseases such as
diphtheria, botulism, rabies, viral
haemorrhagic fever or polio
• A suspected, anticipated or actual event
involving microbial or chemical contamination
of food or water

10. Definitions continue
What is a pandemic?
• A pandemic is a global disease
outbreak. HIV/AIDS is an example of one of
the most destructive global pandemics in
history.
• Note that this is an out break with global
character and lasts for a long duration of time.
• Endemic is Disease that routinely occurs in a
given place

11. Definitions continue
• The term ‘epidemic’ is defined as “the
occurrence in a community or region of cases
of an illness, specific health-related behaviour,
or other health-related events clearly in excess
of normal expectancy.
• The term “outbreak” can actually be used
interchangeably with epidemic and is often
preferable merely because it is a less
frightening term in many situations.

12. TYPES OF OUT BREAKS
1. Common event
This is an outbreak due to exposure of a
group of persons to a harmful influence
that is common to the individuals in the
group, where the exposure is brief.
Common examples include weddings,
matebeto or a party

13. TYPES OF OUT BREAKS
2. Dispersed common source
These outbreaks are due to exposure of a group
of persons in a community to a harmful
influence that is common to the individuals in
the group, These outbreaks are often due to the
consumption of a widely distributed vehicle of
infection transmission, such as a contaminated
food product or reticulated drinking-water.

14. TYPES OF OUT BREAKS
3. Household
An outbreak confined to members of a
single household. Household outbreaks
probably occur frequently, but are likely to
be under-reported. In general, common
event and household outbreaks are
associated with brief and highly localised
exposures.

15. TYPES OF OUT BREAKS
4. Common source in a specific place (or site)
• These outbreaks are due to the exposure of a
group of persons in a community to a harmful
influence that is common to the individuals in the
group, and where all the exposures have
occurred at the same place, but not at the same
time. Typical examples contamination of a
kitchen at fast food restaurant where people
buying food end up with infections.

16. TYPES OF OUT BREAKS
5. Community-wide
An outbreak affecting individuals in a
community, where transmission
predominantly occurs by direct exposure of
susceptible people to infectious host.
Zambia’s examples include an outbreak of
hepatitis A and Cholera

17. TYPES OF OUT BREAKS
6. Institutional
An outbreak confined to the
population of a specific residential or
other institutional setting, such as a
hospital, rest home, prison or boarding
school.

18. Outbreak investigation
• Investigation of disease outbreaks is an
important part of the health department’s
responsibility to protect the public’s health. A
health department may be called on to
investigate a wide variety of unusual health
events, including outbreaks due to food
poisoning, geographic clusters of diarhhoea,
or a mysterious rash illness in a school.

19. Outbreak investigation
• Outbreak investigations can identify the
source of illness and guide public health
intervention. Health departments may
recognize outbreaks through routine
surveillance activities, reports from intelligent
clinicians or laboratorians, or reports from the
persons affected by the outbreak.

20. Outbreak investigation continues
• The public health response by determined by
country legislation, protocols, local reporting
requirements and available resources. Public
health agencies will seek to determine the
nature of the outbreak to define their role in
the investigation.
• Initial information to be collected in a case of
an outbreak should include:

21. Outbreak investigation continues
• The time the outbreak began
• The total number of cases and
unaffected people to calculate the
proportion of people affected
• Symptoms and duration of illness
• Type of outbreak setting

22. Outbreak investigation continues
• Results of any laboratory tests that may have
been done.
• A key means of assessing the initial features of an
outbreak is to assemble a simple line list. A line
list records the basic details about each
suspected case. This includes:
– The time and date of when the illness began
– Duration of illness
– Information on key symptoms
– Whether laboratory tests have been conducted

23. Outbreak investigation continues
• Follow up and review any initial laboratory
tests that may have been conducted
• Develop a preliminary case definition for cases
in the outbreak to assist with counting further
infections
• Review information available, in particular the
type of outbreak setting, characteristics of
cases and attack rate of illness.

24. OUT BREAK INVESTIGATION TEAM
• Successful investigations require a
multidisciplinary approach, effective
communication and collaboration
• Steps in coming up with a team:
–Assemble team members
–Present available information
–Outline plan for investigation and team
communication
–Assign roles and responsibilities

25. Team Member Roles
• Team Leader
– Experience in outbreak investigation and
epidemiology
– Selection can be result of outbreak setting or
etiologic agent
– Role can be filled by:
• County health director,
• Public health nurse,
• Epidemiologist, or
• Environmental health specialist
– Role may change depending on stage of investigation

26. Team Member Roles
• Epidemiologist
– Develop study design and survey
questionnaires
– Create database and conduct data analysis
• Microbiologist
– Verify the diagnosis
– Subtype pathogens to help refine case
definition

27. Team Member Roles
• Environmental health specialists (EHS)
– Collect food and environmental samples
– Provide guidance on food safety regulations and
engineering
• Interviewers
– Collect data in person or by telephone
– Role can be filled by health department personnel,
state or federal personnel, or health science students

28. Team Member Roles
• Clinicians
– Administer vaccines or prophylaxis
– Collect clinical specimens
– Role can be filled by health department or local
medical community
– May include veterinarians, depending
on type of outbreak

29. Team Member Roles
• Regulators
–Facilitate identification of the source of
outbreak and develop prevention
strategies
–Role can be filled by state or federal
agency employees

30. Team Member Roles
• Media Spokesperson
– Deliver clear and consistent messages to
community
– Role can be filled by one outbreak team
member or representatives from each agency
– This has commonly been done by Ministry of
Health Spokesperson

31. Goals of Outbreak Investigations
• To assess the range and extent of the
outbreak
• To reduce the number of cases
associated with the outbreak
• To prevent future occurrences by
identifying and eliminating the source of
the problem
• To identify new disease syndromes

32. Goals of Outbreak Investigations
• To identify new causes of known disease
syndromes
• To assess the efficacy of currently employed
prevention strategies
• To address liability concerns
• To train epidemiologists
• To provide for good public relations and
educate the public

33. Why investigate outbreaks?
Outbreak investigations afford a number of
opportunities for public health department
personnel.
• To involve the public in disease control
• To reduce direct and indirect costs
• To identify new mechanisms of transmission of
known illnesses
• To identify new or emerging disease agents
• To satisfy legal and international obligations

34. Why investigate outbreaks?
• To halt the outbreak and prevent further
illness
• To prevent further outbreaks from the
immediate source
• To prevent further outbreaks from other
similar sources
• To address public concerns

35. Why investigate outbreaks?
Continues
• Research for more knowledge of the
diseases
• To evaluate the effectiveness of
prevention programmes and existing
surveillance
• Control and Prevention measures
• Research Opportunities

36. Why investigate outbreaks?
Continues
• Political or Legal concerns
• Program Considerations
• Finally, outbreak investigations provide
opportunities for training of health
department staff in methods of public
health investigation and emergency
response that are essential in the era of
potential Ebola.

37. Steps of an Outbreak Investigation
• Once an outbreak is identified, there are
several key steps that provide a systematic
approach to investigation. Although these are
listed sequentially, the steps often occur
simultaneously or may be repeated as new
information is received. The outbreak
investigation can be divided broadly into the
preliminary phase, analytic study phase, and
control and follow-up phase.

38. Steps of an Outbreak Investigation
continues
• Components of Outbreak Investigations
Outbreak investigations have diagnostic
(research) and directed action components.
These components are not mutually exclusive.
• Ten Investigatory Steps
Although no single way to investigate an
outbreak applies to all situations, some common
steps prevail. For the sake of efficiency and
completeness, the CDC recommends the
following ten-step approach:

39. Steps of an Outbreak Investigation
continues
• Step 1: Prepare for Field Work
Preparation for an investigation
includes completing the administrative
and personal measures required to
begin the inquiry. Travel preparations
must be made, supplies

40. Steps of an Outbreak Investigation
continues
• Step 2: Establish the Existence of an Outbreak
One of the first tasks in outbreak investigation is
to confirm that the reported cases represent a
true outbreak with a common cause. Often,
purported outbreaks represent sporadic
occurrences of unrelated disease. The
investigator must therefore identify and confirm
all prospective cases and submit each case to
standard diagnostic criteria.

41. Steps of an Outbreak Investigation
continues
• Steps 3 and 4: Verify Diagnoses of Cases and
Search for Additional Cases
If the initial signal of an outbreak is
verified, the next task is to establish a
reliable case definition. Once a reliable
case definition is established, the
epidemiologist submits each prospective
case to these standard criteria for
confirmation of case status.

42. Steps of an Outbreak Investigation
continues
Step 5: Conduct Descriptive Epidemiologic
Studies
• Descriptive epidemiology is used to
explore and describe the general pattern
of disease in the population at risk.
• Descriptive epidemiology has the
following objectives:

43. Steps of an Outbreak Investigation
continues
• To assess data quality for completeness and
accuracy
• To learn about the range and extent of the
outbreak
• To assess the possible source of exposure,
mode of transmission, incubation period,
environmental contributors, host risk factors,
and agent characteristics
• To generate hypotheses about the outbreak

44. Descriptive Epidemiology
• Come up simple characterization of outbreak
by
• Time
• Place
• Person
• Provide clues about the mode of transmission
and vehicle
• Compare group usually needing to put
findings in perspective

45. Steps of an Outbreak Investigation
continues
Step 6: Develop Hypotheses
• A hypothesis is a tentative explanation that
accounts for a set of facts that can be tested
by further investigation. In the investigation of
outbreaks, hypotheses should address the
most likely source of exposure to the etiologic
agent, the means of transmission, the next
steps in the investigation, and future control
measures.

46. Steps of an Outbreak Investigation
continues
• In generating and developing hypotheses
one should consider:
–What is generally known about the
disease
–All relevant clinical and laboratory
findings
–What patients say about the disease

47. Steps of an Outbreak Investigation
continues
• As an educated guess about the cause
and source of an outbreak the hypothesis
has several purposes
• Purpose
• To direct immediate control measures
• To narrow focus of subsequent studies
• To determine the need to involve others
in investigation

48. Steps of an Outbreak Investigation
continues
Steps 7 and 8: Evaluate Hypotheses; As Necessary,
Reconsider or Refine Hypotheses and Conduct
Additional Studies
• Hypotheses developed in step 6 are continually
reexamined, refined, and tested throughout the
investigation.
• The scientific method is iterative, cyclic, and self-
correcting, thus requiring a continual process of
hypothesis generation, hypothesis testing, and
hypothesis refinement.

49. Steps of an Outbreak Investigation
continues
• Since the usefulness of an analytic study is
dictated by the clarity and quality of its
hypothesis, time devoted to hypothesis
refinement is well spent. It is an axiom of
epidemiology that if you cannot generate
insightful hypotheses, then conducting statistical
analyses are likely to be a waste of time.
• Causal hypotheses can be tested using qualitative
or quantitative methods, depending on
underlying circumstances. .

50. Step 9: Implement Control and Prevention
Measures
• Two of the main objectives of outbreak
investigation are to bring the current epidemic
to a halt and prevent future occurrences.
Elements of control should be directed at the
weakest link in the chain of infection.

51. Steps of an Outbreak Investigation
continues
This can involve efforts directed toward any of
the agent, host, or environmental factors that
constitute the ecology of the disease.
Step 10: Communicate Findings
• The investigation is not complete until the
results are disseminated to the appropriate
parties. Study findings should be reported to
initial informants, those involved in authority
and the general public at large

52. Ethical issues in outbreak
investigation
• Ethics and ethical principles extend to all
spheres of human activity. They apply to our
interactions with each other, with animals and
with the environment. A guiding value for
researchers is integrity, which includes a
commitment to the search for knowledge, the
honest and ethical conduct of research and
the dissemination and communication of
results.

53. Ethical issues in outbreak
investigation
• Autonomy: respect the rights of
individuals to self-determination, and
protect those with diminished
autonomy
• Beneficence: maximise possible benefits
• Non-maleficence: minimise possible
harm.

54. Surveillance to detect outbreaks
• Most outbreaks come to the attention of
authorities in one of three ways:
i. By detection of an increased number of cases or
an unusual pattern among cases collected
through formal surveillance systems, such as
disease notifications
ii. By detection of an increased number of cases of
illness collected through informal surveillance
systems, such as self-reported cases of enteric
illness.

55. Surveillance to detect outbreaks
iii. Through an informal alert from a health
care provider or member of the public who
knows of several cases of disease that appear to
have had a common source. This informal
reporting of suspected outbreaks is the most
typical method for identifying common event
outbreaks, and accounts for the largest
proportion of outbreaks reported in Zambia.