Investigation of an Outbreak Flashcards
How do we know about an outbreak?
- From health workers
- General population/citizens
- Media
- Routine analysis of public health surveillance data
– Data analysis shows an increase over normal background level
Why should we investigate outbreaks?
- Control and prevention
- Severity and risk to others
- Research opportunities
- Training opportunities
- Program considerations
- Public, political, or legal concerns
Describe the steps in control and prevention of an outbreak?
- Control the outbreak at hand and prevent future outbreaks
- Assess its extent and the characteristics of the population at risk
- Design measures to prevent additional cases
- Investigate further to identify its source and use that information to develop measures that will prevent future outbreaks
- Strike a balance between instituting control measures and conducting further investigation
Describe the research opportunities in outbreaks?
- Each outbreak offers a unique opportunity to study the natural history of the disease in question
- including the agent, mode of transmission, and incubation period. - Learn more about the impact of control measures and the usefulness of new epidemiological and laboratory techniques
Investigating an outbreak of a disease may highlight what?
Program considerations?
- Populations at risk that have been overlooked
- Failures in the program’s intervention strategy
- Changes in the agent causing the disease
- Events beyond the scope of the program
What are the steps in investigating an outbreak?
- Prepare for field work
- Establish the existence of an outbreak
- Verify the diagnosis
- Define and identify cases
- Describe and orient the data in terms of time, place and person
- Develop hypotheses
- Evaluate hypotheses
- Refine hypotheses and carry out additional studies
- Implementing control and prevention measures
- Communicate findings
How do you prepare for field work?
- Research the disease and gather supplies and equipment
– Review the diseases natural history
– Remember the iceberg phenomenon and potential disease reservoirs - Make necessary administrative and personal arrangements for such things as travel
How do you establish an existence of an outbreak?
Determine if the observed number of cases is greater than the expected number of cases
What is an outbreak or epidemic?
The occurrence of more cases of disease than expected in a given place or among a specific group of people over a particular period of time
What is a cluster?
Grouping of cases in a given place over a particular period of time, without regard to whether the number of cases is more than expected
In what ways does ‘excess’ number of cases not necessarily indicate an outbreak?
- Reporting procedure changes
- Changes in case definition
- Improvements in diagnostic procedures
- Increased interest because of media awareness
- Increased awareness of health practitioners
- Seasonal population changes
How do you verify the diagnosis?
- Confirm that the right diagnosis has been made
- be certain that the increase in diagnosed cases is not the result of laboratory error
- Review clinical findings
- Summarize clinical and laboratory findings
How do you define and identify cases?
1, establish a case definition
2. collect key information
3. analysis - time, person, place
4. establish - causative pathogen and its source
What is a case definition?
a standard set of criteria for deciding whether a person should be classified as having the disease or condition
Name the types of case classifications?
- suspected case
- probable case
- confirmed case
What is a suspected case?
A case that is classified as suspected for reporting purposes
- Some diseases require laboratory confirmation for diagnosis regardless of clinical symptoms, others are diagnosed based on epidemiologic data
- Suspect cases may be dropped when case definition is tightened over the course of the investigation
What is a probable case?
A case that is classified as probable
for reporting purposes
- There may be supportive laboratory results or inconclusive laboratory results
What is a confirmed case?
A case that is classified as confirmed for reporting purposes; usually laboratory-confirmed as a case
What key information do you collect when defining and identifying cases?
- Identifying information
– Name, address, phone - Demographics
– Age, sex, race, occupation - Clinical
– Date of onset, symptoms and signs - Risk Factors
– Helps to focus investigation to the specific disease in question
What is analysis?
Characterize the outbreak by person, time and place
How do you analyze time?
Plot an epidemic curve
- Depicts time course of the outbreak by drawing a histogram of number of cases by their date of onset
Name the types of epidemic curves?
- point source
- continuous common source
- propagated
What is a point source epidemic?
Shape – a steep up slope, a peak and a gradual down- slope
* Interpretation - people are exposed to the same source over a relatively brief period
What is a continuous common source epidemic?
Shape - curve will have a plateau instead of a peak
* Interpretation - people are exposed to the same source over an extended period
