Outbreak Investigation and Prevention & Control Flashcards
Week 9: Epidemiology
1
Q
Levels of disease:
The amount of a disease that is usually present in a community; the observed but not necessarily the desired level; regarded as the expected level of disease
A
Baseline
2
Q
Levels of disease:
A disease that occurs infrequently and irregularly
A
Sporadic
3
Q
Levels of disease:
The constant presence and/or usual prevalence of a disease or infectious agent in a population within a geographic area
A
Endemic
4
Q
Levels of disease:
The persistently high levels of disease occurrence
A
Hyperendemic
5
Q
Levels of disease:
An increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area
A
Epidemic
6
Q
Levels of disease:
Similar to an epidemic but is often used for a more limited geographic area
A
Outbreak
7
Q
Levels of disease: 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 be unknown
A
Cluster
8
Q
Levels of disease:
An epidemic that has spread over several countries or continents, usually affecting a large number of people.
A
Pandemic
9
Q
Aims of outbreak investigation:
A
- To determine the cause of the outbreak (the disease detected)
- To prevent further spread of the outbreak (the fire fighter)
- To educate responsible individuals in the prevention of similar
outbreak in the future (the public health educator)
10
Q
- To determine the cause of the outbreak
A
(the disease detected)
11
Q
- To prevent further spread of the outbreak
A
(the fire fighter)
12
Q
To educate responsible individuals in the prevention of similar outbreaks in the future
A
(the public health educator)
13
Q
5 REASONS FOR INVESTIGATING OUTBREAKS
A
- Prevention and Control
- Gain additional knowledge/ research
- Training
- Public, political, or legal concerns
- Program considerations
14
Q
- Prevention and Control
A
1.1 Primary Public Health reason for investigation
1.2 Principal considerations
-What is the stage of the epidemic?
-Are cases occurring in increasing numbers?
-Is the outbreak just about over?
15
Q
- Prevention and Control:
What is the goal if cases are CONTINUING TO OCCUR:
A
To prevent occurrence of additional
cases
16
Q
- Prevention and Control :
What is the goal if cases are CONTINUING TO OCCUR:
A
To assess the extent of the outbreak, the size, and characteristics of the
population at risk
17
Q
- Prevention and Control:
What is the goal If an outbreak appears to be ALMOST OVER:
A
To prevent similar outbreaks in the future
18
Q
- Prevention and Control:
What is the goal If an outbreak appears to be ALMOST OVER:
A
To identify factors which contributed to the outbreak in order to design and implement measures that would prevent similar outbreaks in the future
19
Q
- Prevention and Control
1.3 How much is known about the ____________, the source, and the mode of transmission of the agent?
A
causative agent
20
Q
1.4 The decisions regarding whether and how extensively to investigate an outbreak are influenced
by ________________.
A
the characteristics of the problem itself
21
Q
- Gain additional knowledge/ research
- Each outbreak is __________ the natural history of the disease in question.
A
an opportunity to study
22
Q
- Gain additional knowledge/ research
- For a newly recognized disease, ____________ provides an opportunity to define the natural history –agent, mode of transmission, and incubation period, and the clinical spectrum of the disease
A
field investigation
23
Q
For a newly recognized disease, field investigation provides an opportunity to define the natural history – _____________.
A
- agent,
- mode of transmission
- incubation period,
- clinical spectrum of the disease
24
Q
Are able to characterize the populations at greater risk:
identify specific risk factors (ex. Legionnaires disease in
Philadelphia in 1976; Toxic Shock Syndrome in 1980, AIDS
in early 1980’s, Eosinophilia-myalgia-syndrome in 1989)
A
- Gain additional knowledge/ research
25
Assessing the impact of control measures
2. Gain additional knowledge/ research
26
Investigating an outbreak requires a combination of diplomacy, logical thinking, problem-solving ability,
quantitative skills, epidemiologic know-how, and judgment.
3. Training
27
These skills improve with practice and experience
3. Training
28
The investigating team can be composed of a seasoned
epidemiologist with trainee/s.
3. Training
29
These concerns sometimes override scientific concerns in the decision to conduct the investigation.
4. Public, political, or legal concerns
30
Increasingly, the public has taken an interest in ‘disease clusters’ and potential environmental exposures, and has called upon the health department to investigate
4. Public, political, or legal concerns
31
* An outbreak of a disease (which is targeted by the public health program) may reveal a weakness in that program and provide an opportunity to modify/strengthen the program’s efforts.
5. Program considerations
32
* Investigating the causes of an outbreak may identify populations that may have been overlooked, failures in the investigation strategy, changes in the agent, or events beyond the scope of the program
5. Program considerations
33
8 STEPS IN AN OUTBREAK INVESTIGATION
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 * Do immediate control measures
5 * Formulate and test hypothesis
6 * Plan and execute additional studies
7 * Implement and evaluate control measures
8 * Communicate findings
34
PREPARATION FOR FIELD-WORK
* Investigation
* Administration
* Consultation
35
Appropriate scientific knowledge, supplies, and equipment; consult regarding epidemic, laboratory
specimen collection, storage, and transport
INVESTIGATION
36
Travel arrangements and travel orders
ADMINISTRATION
37
Specific roles and responsibilities
CONSULTATION
38
6 KNOWLEDGE NECESSARY TO PREPARE FOR OUTBREAK
INVESTIGATIONS
1. Various types of etiologic agents and the resultant diseas:
2. Epidemiologic characteristics of outbreaks associated with different
etiologic agents or resultant diseases;
3. Clinical symptoms of resultant diseases;
4. Environmental and food sanitation practices;
5. Sources of exposure which are vulnerable to contamination with an
infectious or chemical agent;
6. Laboratory test available to determine causative agent
39
* Confirm laboratory testing;
* Rule out misdiagnoses or laboratory error
1 * Verify the diagnosis and confirm the outbreak
40
Under the "Verify the diagnosis and confirm the outbreak"
A. Knowledge/Awareness of an existence of an epidemic through.
B. Initial investigation may turn out to be.
C. Comparison of the number of the observed number of
cases with the expected number which can be
D. Source of data to establish ‘expected number cases.
E. Factors which could explain excess cases.
F. Factors influencing decision regarding investigation of the
outbreak
41
Knowledge/Awareness of the existence of an epidemic
through:
Ø Regular analysis of surveillance data- detect unusual patterns of disease occurrence.
Ø Calls from a health care provider or a citizen who knows of several cases.
Ø Media reports
42
Initial investigation may turn out to be
Ø True outbreaks with a common cause;
Ø Sporadic and unrelated cases of the same disease
Ø Unrelated cases of similar but unrelated disease (i.e.,
without a common cause)
43
C. Comparison of the number of the observed number of
cases with the expected number which can be:
Ø The number of cases from the previous few weeks or
months, or
Ø The number of cases from a comparable period during
the previous few years
44
D. Source of data to establish ‘expected number cases'
Ø Health department surveillance data if disease is a
notifiable disease
Ø Hospitals discharge records, mortality statistics, cancer
or registries if disease is non-notifiable
Ø Apply rates from neighboring areas or conduct an
informal survey among local physicians
Ø Conduct survey of the community to establish
background level of the disease
45
F. Factors influencing decision regarding investigation of the
outbreak
Ø Severity of the illness
Ø The potential for spread
Ø Political consideration
Ø Public relations
Ø Availability of resources, etc
45
E. Factors which could explain excess cases
46
2 * Define a case and conduct case finding
* Develop a specific case definition using: (symptoms or laboratory results, time period, location)
* Conduct surveillance using case definition:
- existing surveillance
-active surveillance
* Interview case-patients
47
CASE DEFINITION
- Allows a simple, uniform way to identify cases
- “standardizes” the investigation
- Is unique to outbreak but is based on objective criteria
48
“standardizes” the investigation
CASE definition
49
Is unique to outbreak but is based on objective criteria
CASE definition
50
Allows a simple, uniform way to identify cases
CASE definition
51
True or False: In CASE definition we always includes: Person, Place and Time
TRUE
52
Relevant information about personal characteristics
Person
53
Information about where the exposure is thought to
have occurred
Place
54
Dates during which exposure was thought to have occurred
Time
55
56
CATEGORIES OF CASES
1. Confirmed
2. Probable
3. Suspected
57
* Symptoms characteristic of the agent
* Lab test
* Epidemiologic link
Confirmed
58
*Symptoms confirmed
*No lab or epidemiologic link
Probable
59
*Symptoms are reported but not
confirmed
*No lab or epidemiologic link
Suspected
60
Who was infected?
What do the cases have in common?
PERSON
61
Where were they infected?
May be useful to draw a map
PLACE
62
When were they infected?
Create an epidemic curve
TIME
63
3 * Tabulate and Orient data
What is a graphical depiction of the number of cases of illness by
the date of illness onset?
EPIDEMIC CURVE
64
Can provide information on the following characteristics of
an outbreak
a. pattern of spread
b. magnitude
c. outliers
d. time trend
e. exposure and/or disease incubation period
65
The overall shape of the epidemic curve can reveal the
type of outbreak
1. common source (point, continuous, intermittent)
2. Propagated
3. Mixed
66
People are exposed continuously or intermittently to a harmful source
COMMON SOURCE
67
Period of exposure maybe brief or long
68
Intermittent exposure often results in an epi curve with
irregular peaks that reflect the timing and the extent of
exposure
COMMON SOURCE
69
* Cases were all exposed to the same source during a brief
period of calendar time;
* Typically shows a sharp upward slope and a gradual
downward slope
* Is a common source outbreak in which the period of
exposure is brief, and all cases occur within one incubation
period
COMMON SOURCE – Common Point Source
70
Continuous exposure will often cause cases to rise
gradually (and possibly to plateau, rather than to peak)
Continuous exposure
71
Is spread from person-to-person
PROPAGATED EPIDEMIC
72
Disease agent may replicate in a susceptible host as part of
the transmission cycle
PROPAGATED EPIDEMIC
73
May have multiple waves
74
The classic epi curve for a propagated outbreak has
progressively taller peaks, one incubation period apart
PROPAGATED EPIDEMIC
75
Involve both a single, common exposure to an infectious
agent and secondary propagative spread to other individuals (e.g., person to person transmission
MIXED EPIDEMIC
76
FACTORS AFFECTING DURATION OF AN EPIDEMIC
1. The number of susceptible persons whoa re exposed to a
source of infectious and become infected;
2. The period of time over which susceptible persons are
exposed to the source
3. The minimum and maximum incubation periods for the
disease.
77
* A special cumulative incidence ( or incidence proportion)
that measures the proportion of persons in a population
who experience an acute health event during a limited
time (e.g., outbreak)
ATTACK RATE
78
Number of new cases of a health problem during an outbreak divided by the size of a population at the
beginning of the period who are at risk of the event
ATTACK RATE
79
The frequency of new cases of a disease among the contacts of known patients
SECONDARY ATTACK RATE
80
The ratio of the number cases among contacts occurring
within the acceptable incubation period following exposure to a Primary Case to the total number of
exposed contacts.
81
Can provide a sense of the magnitude of an outbreak
Additional information can be obtained by stratifying
the epi curve
OUTBREAK MAGNITUDE
82
Outliers are cases at the very beginning and end that
may not appear to be related to the rest of the cases
OUTBREAK OUTLIERS
83
If the timing of the exposure is known, epi curves can be
used to estimate the incubation period of the disease
PERIOD OF EXPOSURE/INCUBATION PERIOD FOR THE OUTBREAK
84
Prevention
* to hinder
* to make impossible by advance
* individuals and community
85
Control
* to hold in check
* to restrain
* community and population
86
refers to aggregation of two or more diseases in a population in which
there is some level of positive biological interaction that exacerbates the negative health effects of any or all of the diseases
Syndemic
87
* the objective of the applied measure is limited to the protection of
health or the presence of the disease in a person
Individual
88
use of measure directed towards the community with the objective of
reducing the morbidity and mortality caused by the disease in the community
Disease Control
89
90
91
situation in which cases of the disease no longer exist but one or more factors potentially important in the occurrence still persist
Elimination of disease
92
* Total wipe out of disease and agent of disease
. Eradication
93
