what is an outbreak?
- A sudden and rapid increase in the number of cases of a disease or condition among a population
- Usually defined as two or more cases of the same type of illness occurring at about the same time
How can you recognize an outbreak?
- When someone first notices an unusual disease or an unusual number of cases of a disease and alerts a PBH official
- comes from surveillance data but it is uncommon for outbreaks to be detected this way
Why should an outbreak be investigated?
- E might still be in progress and by identifying and eliminating the source of infection additional cases can be prevented
Why should an outbreak be investigated when it is over?
= can prevent similar outbreaks
= describes the new disease and learn more about it
= Evaluating existing prevention strategies
= Teach epidemiology
= Address public concerns about the outbreak
What is done after a decision is made to investigate an outbreak?
Epidemiologic investigation
Environmental investigation
Interaction with the public, press, and legal system
What are the constraints of an epidemiological investigation?
- If the outbreak is ongoing at the time of the investigation there is an urgency to find the source and prevent it
- In many outbreaks, the number of cases is limited
- Early media reportings might be bias
- Legal liability and financial interests put pressure on doing quick investigations
- If detection of an outbreak is delayed, useful clinical and environmental samples might be hard to find
order of outbreak
- Establish case definition
- Confirm cases are related
- Establish the background rate of disease
- Find cases, decide if there is an outbreak, and define the scope of the outbreak
- Examine the descriptive epidemiological features of the case
- Generate hypothesis
- Test hypothesis
- Collect and test environmental sample
- Implement control measures
- Interact with the press and inform the public
What makes a good case definition?
Set of standard criteria used to determine if a person has a particular illness of disease
Person place time
Disease symptoms
Confirmed lab samples
What is descriptive epidemiology?
Collecting patient data, and case finding can give important information
how can samples be stored in enviornmental investigations?
Since it is expensive to test environmental samples its fine to collect and store as many samples as possible and test only a few
What is an epi curve and how can it help an outbreak?
- Graphical depiction of the number of outbreak cases by date of illness onset
- Useful because it gives information on the outbreak pattern/speed, magnitude, outliers, time trend, and exposure/incubation period
What is a histogram and bar chart ?
Histogram: frequency distribution of continuous data and not separated by a gap
Bar chart: compare discrete categories of data separated by a gap
What can the pattern/shape tell you?
The overall shape reveals the type of outbreak - common source, point source of propagated
common source outbreak
people are exposed intermittently or continuously to a common harmful source
The period of exposure may be long or short
It is common and results in irregular peaks that reflect the timing and extent of exposure
What is a point source outbreak?
Sharp upward slope and gradual downward slope
It is a common one where the exposure period is brief and all cases happen within one incubation period
What is a propagated outbreak?
Spreads person to person which makes them last longer than common source epidemics and leads to multiple waves of infection
Progressively taller peaks, each an incubation period apart
