Epcm l16 outbreak investigations

EPIDEMIOLOGY & COMMUNITY MEDICINE
WRITTEN AND COMPILED BY EPCM 361 COURSE COMMTTEE
Third year
Level 6
Lecture 14
Outbreak investigations

• Define the outbreak
• Explain the targets of outbreak investigations
• List the warning signals of outbreak investigations
• Discuss steps of an outbreak investigation

• Level of disease:
• Baseline/endemic level of the disease: The amount of a
particular disease that is usually present in a community is
referred to as, and is often regarded as the expected level of
the disease.
• Sporadic refers to a disease that occurs infrequently and
irregularly.
• Endemic refers to the constant presence and/or usual
prevalence of a disease or infectious agent in a population
within a geographic area.
• Hyperendemic refers to persistent, high levels of disease
occurrence. Occasionally, the amount of disease in a
community rises above the expected level.

Level of disease: (cont.)
• Epidemic refers to an increase, often sudden, in the number of
cases of a disease above what is normally expected in that
population in that area.
• Outbreak carries the same definition of epidemic, but is often
used for a more limited geographic area.
• Cluster refers to an aggregation of cases grouped in place and
time that are suspected to be greater than the number
expected, even though the expected number may not be
known.
• Pandemic refers to an epidemic that has spread over several
countries or continents, usually affecting a large number of
people.

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 (pandemic).
It may last for a few days or weeks, or for several years.

• Epidemics occur when an agent and susceptible hosts are
present in adequate numbers, and the agent can be effectively
conveyed from a source to the susceptible hosts.
An epidemic may result from:
• A recent increase in amount or virulence of the agent,
• The recent introduction of the agent into a setting where it has
not been before,
• An enhanced mode of transmission so that more susceptible
persons are exposed,
• A change in the susceptibility of the host response to the agent,
and/or
• Factors that increase host exposure or involve introduction
through new portals of entry.

Ways to recognize an outbreak:
–Routine surveillance activities
–Reports from clinicians and laboratories
–Reports from affected individuals

1. Primary- to control the spread of disease
2. To determine the causes of disease, its source &
mode of transmission
3. To determine who is at risk
4. To know magnitude of the problem
5. To determine the effectiveness of control measures
6. To identify methods for present & future prevention
& control
7. Research & training opportunities
8. Public, Political and legal concerns

1. Clustering of cases/deaths in time/space
2. Unusual increase in cases/deaths
3. Shift in age distribution of cases
4. High vector density
5. Acute hemorrhagic fever or acute fever with renal
involvement/altered sensorium
6. Severe dehydration following diarrhea in patients
above 5 years age.

1. Verify the diagnosis and confirm the outbreak
2. Define a case and conduct case finding
3. Tabulate and orient data: time, place, person
4. Formulate and test hypothesis
5. Take immediate control measures
6. Plan and execute additional studies
7. Post-epidemic Measures
8. Prepare Written Report

Specialists Auxiliaries
1. Epidemiologist 1. Nurses
2. Clinician (pathologist) 2. Specialist assistants
3. Microbiologist 3.Secretary/Interpreter
4. Veterinarian 4. Driver
5. Entomologist
6. Mammologist
7. Sanitary engineer
8. Toxicologist
9. Information Specialist

• It consists of collecting & testing appropriate specimens.
To identify the etiologic agent, the collection need to be
properly timed.
• Examples of specimens include - food & water, other
environmental samples (air settling plates), and clinical
(blood, stool, sputum or wound) samples from cases &
controls.

• Develop a specific case definition using:
–Symptoms or laboratory results
–Time period
–Location
• Conduct surveillance using case definition
–Existing surveillance
–Active surveillance (e.g. review medical records)
• Interview case-patients

• Create line listing
• Person
–Who was infected?
–What do the cases have in common?
• Place
–Where were they infected?
–May be useful to draw a map
• Time
–When were they infected?
–Create an epidemic curve

As soon as the preliminary data indicate the
magnitude & severity of the outbreak, a hypothesis
should be made regarding time, place and person;
the suspected etiological agent & the mode of
transmission.

• Simultaneous to data collection & hypothesis
formation, steps should be taken to contain the
epidemic.
• These measures depend upon knowledge of
etiologic agent, mode of transmission & other
contributing factors.
• Protective measures are necessary for patients
(isolation & disinfection), their contacts
(quarantine) and the community (immunization,
etc.).

Because there may be a need to find more
patients, to define better the extent of the
epidemic, or because a new lab method or
case finding method may need to be
evaluated, the epidemiologists may want to
perform more detailed & carefully executed
studies.

• The efficacy of control measures should be
assessed day by day during the outbreak, a final
assessment being made after it has ended.
• This will provide a logical basis for post-epidemic
surveillance & preventive measures aimed at
avoiding the repetition of similar outbreaks.

• The final responsibility of the investigative team is to
prepare a written report to document the
investigations, findings and the recommendations.
• The written report should be submitted, in a
standardized format, to the public health
authorities including the ministry of health & remain
confidential until it has been given official
permission.

• Epidemiologic Surveillance & Outbreak Investigation.
Textbook of Epidemiology and Biostatistics in Preventive
Medicine. W B Saunders Publication. 43-53.
• Bres P. Public Health Action in Emergencies caused by
Epidemics – A Practical Guide. Geneva. WHO. 1986.

Epcm l16 outbreak investigations

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