Investigation of an Outbreak Flashcards
What is an outbreak?
a sudden rise in the number of cases of a disease in a community or a limited geographical area
What is an epidemic?
Rapid Increase in the number of cases than what is normally expected but spread over a large geographical area
What is a pandemic?
is an epidemic that’s spread over multiple countries or continents
What is an endemic?
is when a disease is regularly present in a population
- if it’s not quickly controlled, an outbreak can become an epidemic
How do we come to 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 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 an outbreak presents?
- 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 in terms of 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 the existence of an outbreak?
Determine if the observed number of cases is greater than the expected number of cases
1. 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
2. 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
Note: Excess may not necessarily indicate an outbreak
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
What is a case definition?
a standard set of criteria for deciding whether a person should be classified as having the disease or condition
Give examples 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
How do you define and identify cases?
Collect key information
- 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 the descriptive epidemiology of an outbreak?
Characterize the outbreak by person, time, and place
How do you characterize an outbreak by time?
Plot an epidemic curve
- Depicts time course of the outbreak by drawing a histogram of number of cases by their date of onset/presentation
Name the 3 shapes of endemic curves?
- Point source epidemic
- Continuous common source epidemic
- Propagated epidemic
Describe the shape + interpretation of a point source epidemic curve?
- Shape - a steep up slope, a peak and a gradual down-slope
2. Interpretation - people are exposed to the same source over a relatively brief period
Describe the shape + interpretation of the continuous common source epidemic curve?
- Shape - curve will have a plateau instead of a peak
2. Interpretation - people are exposed to the same source over an extended period
Describe the shape + interpretation of a propagated epidemic curve?
- Shape - a series of progressively taller peaks
2. Interpretation - person-to-person spread
What is the importance of of characterizing an outbreak by place?
Provides geographic extent of problem
May demonstrate clusters or patterns that provide important etiologic clues
How do you characterize an outbreak according to place?
Spot map useful for illustrating where cases live, work or may have been exposed
Importance of characterizing an outbreak by person?
Determine the populations at risk by characterizing the outbreak by person
Define populations by personal characteristics
- Examples: age, race, sex, or medical status
Assess for exposures
- Examples: occupation, leisure activities, use of medications, tobacco, drugs
Hypotheses may be based on?
- Interviews with affected people
- Consultation with health officials
- Descriptive epidemiology
When developing a hypothesis what should you try to address?
- Causative agent
- Mode(s) of transmission
- Exposure(s) that caused the disease
- Outlier cases (ones you think might not have anything to do with the others) can sometimes provide important clues
What is done in the evaluation of the hypotheses?
Compare hypotheses with the established facts using analytic epidemiology
Describe the analytic epidemiology used when evaluating hypotheses?
- Cohort studies
- Relative risk (ratio of attack rates) can be calculated
- Best for analyzing an outbreak in a small well-defined population - Case-control studies
- Odds ratio can be calculated
- population in an outbreak is not well defined
How do you refine/reconsider a hypothesis?
- Hypotheses not confirmed: consider new vehicles or modes of transmission
- Conduct additional epidemiologic studies
- Laboratory e.g serology
- Environmental
Describe what is done in implementing control and prevention measures of an outbreak?
- interrupting transmission or exposure
- Isolation of symptomatic individuals
- Quarantine
- Instruct avoidance of exposure areas - reducing susceptibility
- immunizations
- Chemoprophylaxis - Universal Precautions
- Using personal protective equipment
How do you communicate findings in a the investigation of an outbreak?
- an oral briefing
2. a written report
