Disease Outbreak Flashcards
Define the term “outbreak.”
The occurrence of more cases than expected – occur frequently (CDC, 2012).
OR
Disease of health-related event occurring in excess than would be normally expected for a given time period, area or among a specific group of people or animal
OR
A series of disease events clustered in time (Stevenson, 2008)
An outbreak may involve…
part of a herd, a whole herd, a country, or the world
Outbreaks can be a more ________ in nature
… causing _______ losses in a population of animals over an _______
period of time before being ________, _________, and ________.
insidious, subclinical, extended, identified, characterized, investigated
Define the term “epidemic.”
Epidemic – same definition as ‘outbreak’, but usually for a larger geographic
area (CDC, 2012)
Define the term “pandemic.”
Pandemic – an epidemic that has spread to several countries or continents
(CDC, 2012)
What are the sources of information you can utilize during an outbreak? Which are local, regional, and national/international sources?
- Reports from field veterinarians
- Reports from producers
- Herd records
- Report from laboratories
^ Local - Routine surveillance activities
- General public / media
^Regional - Online web-servers
- e.g. ProMed, HealthMap, OIE,
WHO
^National/International
- e.g. ProMed, HealthMap, OIE,
What are the overall goals of an outbreak investigation?
- Identify source of illness
- Put in place timely health control interventions to stop the outbreak
(prevent new cases) - Increase our knowledge of disease (mode of transmission, risk factors, etc.)
- Prevent new episodes (outbreaks)
- Evaluate or establish a surveillance system
What do you want to identify during an outbreak?
- Causal agent
- Mode of transmission
- Source of infection
- Carriers (if any)
- Population at risk
- Risk factors associated with disease
What are the 8 steps of an outbreak investigation?
How do you verify an outbreak?
- Before leaving for investigation
- Gather preliminary information about an outbreak
- Area affected, species involved, animal health situation
- Likely causes of disease
- Gather preliminary information about an outbreak
- What is the problem?
* Characterize the problem with the aim to formulate a working case definition
* Verify clinical signs, morbidity and mortality- These include subclinical signs such as: Sudden reduction in feed/water consumption, sudden death and high mortalities, etc.
- Not every case needs to be lab-confirmed
- You can still investigate without knowing the agent
- Is there a true excess of cases?
* Emerging diseases (even with just 1 case!)- WHO def: “[a disease] that has appeared in a population for the first time, or that may
have existed previously but is rapidly increasing in incidence or geographic range.”
*Is the disease event clustered in time, place or animal/person - Don’t rely entirely on rumors, people/employee’s memories and/or perceptions
* Be aware of artefactual causes of increase (or decrease) frequencies in reporting cases (changes in local reporting practices, increased interest, etc.)
- WHO def: “[a disease] that has appeared in a population for the first time, or that may
How do you establish a case definition?
- A case definition:
* Allows for a simple and uniform way to identify cases
* It is the operational definition of a disease- Standardizes the investigation!
- Good case definitions have two parts – they specify:
1) The characteristics of the population at risk
2) What distinguishes cases from other members of the population- Clinical information about the disease (clinical signs, lab results)
* Ensures that the outcome is consistently defined across space and over time
- Clinical information about the disease (clinical signs, lab results)
When you are establishing a case definition, how do you categorize cases?
Confirmable is the best.
How do you enhance surveillance?
–> Conduct surveillance using _____ definition:
1. Active surveillance (______ investigation)
* Interview __________ regarding recent animal ___________, cases in neighborhood, etc.
2. Intensive surveillance is required to:
* accumulate enough cases on which to draw ___________
* document _______ (or ______) to recommend interventions
3. At the national level: _____ coverage are effective tools for enhancing surveillance
* e.g. radio and television, producer organizations/publications
–> Conduct surveillance using case definition:
1. Active surveillance (field investigation)
* Interview producers regarding recent animal movement, cases in neighborhood, etc.
2. Intensive surveillance is required to:
* accumulate enough cases on which to draw conclusions
* document success (or failure) to recommend interventions
3. At the national level: media coverage are effective tools for enhancing
surveillance
* e.g. radio and television, producer organizations/publications
When enhancing your surveillance efforts, how do you conduct surveillance using the case definition?
Animals exposed can have different infection statuses. During the infected stage, the animal will exhibit different clinical signs (disease status).
How do you describe an outbreak?
- Person/Animal (who?) :
* Identify which ones were infected
* What are the species, breed, sex, age, diet…
* Compare number of affected with non-affected - Place (where?) :
* Locations of infected animals/people
* Create maps with cases distribution (rough sketch/maps/GPS/GIS) - Time (when?) :
* When were they infected?
* Create an epidemic curve using various time intervals (to tell you when they occurred in time and space).
* Establish type of outbreak – point source or propagated, etc.
We are missing the baseline.
This graph is what type of point source?
The lack of propagation period is what makes this unique.
This graph is what type of point source?
What type of point source is this?
e.g. floods –> spore release
What type of epidemic curve is this?
Propagative
aka person-to-person or animal-to-animal
What type of epidemic curve is this?
index case with propagation
What do you do If only the time of onset of
illness is known and epidemic curve suggest point source outbreak?
- Determine the median time of
onset of illness - Calculate the time between
occurrence of the first and last
case (width of the epidemic curve) - Count back this amount of time
from the median to obtain the
probable time of exposure
What do you do If the organism and the time of onset of illness are known and epidemic curve suggests a point- source outbreak?
- Find the minimum and the maximum
incubation period for the disease - Identify the last case and count back
on the x-axis one maximum
incubation period - Identify the first case of the epidemic
and count back the minimum
incubation period - Ideally, the two dates will be similar
and represent the probable period of
exposure - Alternatively, identifying the peak of the
epidemic and count back one average
incubation period – the probable time of
exposure
* This method is useful in ongoing
outbreaks in which the last cases have
not yet appeared - These methods cannot be used if
secondary spread is involved or exposure
is prolonged
Tool to help you determine sample sizes necessary to test your hypothesis.
Do not need to know
Gray line is a rough rule of thumb.
What does the odds ratio tell us?
What stands out to you here?
Odds ratio is protective, so eating pork would have helped you.
Morbier stands out here. If it does not cross one = significant aka eating this type of cheese = having salmonella.
if it does cross one = not significant
This concept is for the confidence interval
Calculate the odds of exposure in D+, D-, and the Odds ratio.
Then calculate the Odds of Disease in E+, E-, and OR in OE+ and OE-.
Label this graph accordingly.
