Outbreak Investigation Methods Flashcards
Outbreak investigation steps (10)
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 and test hypotheses (analytic epidemiology)
8) Plan for additional studies
9) Implement and evaluate control measures
10) Communicate finding
Outbreak investigation step 1: prepare for field work
• Investigation needs
- Supplies
- Laboratory
- Expertise
• Administrative needs
- Team leader
- Procedures
• Logistics and dynamics
- Where to go/Who to meet
- What is your role
Outbreak investigation step 2: determine existence of outbreak
• Outbreak, epidemic, and cluster - Grouping of cases in a given place or time is a cluster ; No difference between an outbreak and epidemic (Both describe an increase in cases over what is expected)
• Real vs. Artifact: changes in surveillance methodology can result in the appearance of an outbreak when there really isn’t one
Outbreak investigation step 3: confirm diagnosis
• Ensure proper diagnosis - Do all individuals have the same disease? ; Laboratory error?
• Examine initial case-patients
• Review medical records
Outbreak investigation step 4: identify and count cases
• Who is a case?
• Index Case: refers to the first case in a disease outbreak
• Sometimes recognized/known, sometimes not
• Need a working case definition to identify and count cases!
• Essential to standardize the case definition to find cases no matter where they are and who the investigators are
Index case definition
First case in disease outbreak
Working case definition: 4 components
Clinical presentation
Who/person
Where/place
When/time
Categories of certainty in working case definition (3)
Confirmed
Probable
Possible
Common symptoms of an outbreak (7)
• Fever
• Nausea
• Diarrhea
• Vomiting
• Headache
• Rashes
• Stomach pain
What allows you to begin establishing the case definition
Typical signs and symptoms reported in outbreak
Importance of consistent case definition: AIDS example
Expansion of surveillance case definition resulted in huge spike in number of reported cases
Outbreak investigation step 5: tabulate data and perform descriptive epi
• Organize case information identified in Step 4 into a line listing
• Perform descriptive epidemiology:
Time: Epidemic curve
Place: Orient to areas of concern (Spot map)
Person: Describe case group ( Numerators and denominator)
Epidemic curve definition
Graphical depiction of number of cases of illness by date of illness onset
Usually a bar graph
How can epidemic curve help in an outbreak (2)
• Can provide information about the outbreak
-Pattern of spread (e.g., Did person-to-person transmission occur?)
- Magnitude
- Time trend
-Exposure and/or period of incubation
• Different shapes reveal the type of outbreak
•-Common Source: all cases are exposed to agent from same source( Point source vs Continuous source vs Intermittent )
- Propagated source: secondary cases exposed to primary cases
Outbreak investigation step 6: consider implementing control measures
• Target to:
-Eliminate the source
- Interrupt transmission
- Reduce susceptibility
Outbreak investigation step 7: develop and test hypotheses
• Review descriptive epidemiology (Explain outliers)
-Generate Hypotheses
• Analytic epidemiology options - Cohort study, Case-control study
• Compare results with hypothesis
Outbreak investigation step 8: plan for additional studies
• Improve quality of numerator and
denominator data
• Environmental studies
• Laboratory studies
Outbreak investigation step 9: implement and evaluate control measures
• Evaluate impact of control measures taken at Step 6
• Modify as needed
• Active surveillance to monitor for new cases
Outbreak investigation step 10: communicate findings
• Why?
-Document findings
- Justify recommendations
- Document for legal purposes
Methods
• Written report
• Oral presentation to stakeholders
• Publication in public health bulletins, journals
Point source epidemic: curve description
Single sharp rise and fall on epi curve
Continuous source epidemic curve description
Curve flattened and more spread out
Intermittent source epidemic curve description
Repeated gaps in case onset dates
Propagated source epidemic curve description
Secondary cases exposed to primary cases
Subsequent peaks higher than initial peak
