Lecture 17- Outbreak Investigation Methods Flashcards
What are the 10 steps in outbreak investigations
1.prepare for field work
2. Determine the existence of an outbreak
3. Confirm the diagnosis
4. Identify and count cases
5. Tabulate data and perform descriptive epidemiology
6. Consider implementing control measures
7. Develop hypotheses (analytic epidemiology)
8. Plan for additional studies
9. Implement and evaluate control measures
10. Communicate findings
Prepare for field work what are the investigation and administration needs as well as logistics and dynamics
Investigation needs: supplies, lab, expertise
Administrative needs: team leader, procedures
Logistics and dynamics: where to go/who to meet, what is your rople
Determine the existence of an outbreak
Is it an outbreak, epidemic or cluster
Real vs. artifcat
What is a cluster
Grouping of cases in a. Given place or time
What is the difference between real vs artifact
Changes in surveillance methodology can result in appearance of an outbreak when there isn’t one
Confirm the diagnosis
Ensure proper diagnosis- do all individuals have same disease, lab error?
Examine initial case patients, review medical records
Identify and count cases
Who is a case, index case, case definition
What is an index case
Refers to the first case in a disease outbreak
What is a working case definition
Criteria: 4 components
Clinical presentation
Who
Where
When
What are the categories of certainty
Confirmed, probable, possible
What are common symptoms of an outbreak
Fever, nausea, diarrhea, vomiting, headache, rashes, stomach pain
Tabulate data and perform descriptive epidemiology
Organize and visualize data, identify patterns, identify possible causative agents based on symptom onset and incubation period, identify possible exposure sources based on symptom onset
Perform descriptive epidemiology
Descriptive epidemiology for time, place and person
Time: epidemic curve
Place: orient top areas of concern-spot map
Person: describe case group
What is line listing and what is collected
Table or database of case information
Information collected: demographic, clinical, epidemiological
Epidemic curve
Graphical depiction of the number of cases of illness by the date of illness onset
What are two types of epi curves
Common source
Propagated source
What is a common source epidemic curve
All cases are exposed to agent from the same source
Point source, continuous source, intermittent sourc
What is a propagated source epidemic curve
Secondary cases exposed to primary cases
What information does epidemic curve provide
Patterns of spread, outliers, magnitude, time trend, exposure and/or period of incubation
Different shapes of graph reveal the type of outbreak
Consider implementing control measures
Target to:
Eliminate the source, interrupt transmission, reduce susceptibility
Develop and test hypothesis
Review descriptive epidemiology, explain outliers, generate hypothesis, analytic epidemiology, compare results
What are the two case design options for analytic epidemiology
Cohort study and case control study
Odds ratio
Measures strength of association between exposures and outcomes in case control studies
OR=ad/bc
Odds ratio +1
No difference between expose and outcome
Odds ratio <1
Protective effect- the outcome is less likely in the exposed group
Odds ratio >1
Outcome is more likely in exposed groups the higher the number the stronger the association
Attack rate formula
(# new cases/ # in population rise) x 10^n
What is the food specific attack rate formula
(# ill persons who ate food/ total # who ate the food) x100
Plan for additional astudies
Improve quality of numerator and denominator data
What are two additional study types
Environmental and laboratory
Implement and evaluate control measures
Evaluate impact of control measures taken at step 6, modify as needed, active surveillance to monitor for new cases
Communicate findings
Document, justify recommendations
