Outbreaks and outbreak investigation Flashcards
Define outbreak
Variable definitions
A sudden rise in disease incidence
More cases of a particular disease than expected in a given area, or among a specific population, over a particular period of time.
Why investigate an outbreak?
Determine source Transmission Financial costs Future prevention Zoonosis potential Control Ascertain severity Opportunity for research and training Reassure public and communicate to them Minimise social and financial disruption Make recommendations of strategies to prepare for the future
Outline a systematic approach to outbreak investigation - 8
- Confirm the existence of an outbreak
- Establish a diagnosis
- Determine magnitude of problem
- Analyse the problem - who, where, when?
- Develop a working hypothesis
- Evaluate (test) working hypothesis
- Further data collection and analysis (e.g. perform an economic analysis)
- Communicate findings
How can you confirm the existence of an outbreak?
Increased morbidity/mortality over time and clustered in space
COMPARE WITH: What is the expected number of cases for the area in the given time frame?
What should you do if you suscpect a notifiable disease?
Notify the nearest APHA office (your local one should be open 24/7. If not, call the Weybridge Head Office)
How do you analyse the problem (stage 4 of strategic approach to an outbreak)?
Describe and orient data in terms of time, place, herd/flock/farm:
a. ANIMAL PATTERN - who? (signalment and risk factors)
b. SPATIAL PATTERN - where? (clustering, ID source, sketch map and label with cases)
c. TEMPORAL PATTERN - estimate the incubation and exposure periods, draw an epidemic curve to estimate where you are in the course of an epidemic, estimate probable time periods of exposure, draw inferences about the epidemic pattern
What is an epidemic curve?
X AXIS: time (date, number of days since first case etc)
Y AXIS = incidence (i.e. number of NEW cases). If this axis shows cumulative total of cases, this is NOT a true epidemic curve.
What is a propagated epidemic?
One that is spread from animal to animal
What are the 2 types of mathematical model that can be used to simulate disease spread in a population?
DETERMINISTIC: simplest model, assumes population is homogenous and that the only distinction is their disease state.
STOCHASTIC: takes into account the effects of chance.
What is basic reproduction number (R0)?
The average number of new cases caused by one infected individual in an entirely susceptible population.
What does the R0 depend on? 3
Contact rate - direct or indirect, reduced by movement restrictions.
Infectiousness
Susceptibility
What does R0<1 signify?
That the outbreak is contained.
