1a.30 Epidemic Theory and analysis of infectious disease data Flashcards
Epidemic definition
An epidemic is the occurrence of a number of cases of a disease that exceeds the number of cases normally expected for that disease in that area at that time
What techniques are used for analysing infectious disease data?
Epidemic curves
Exceptional reporting
Identification of significant clusters
What are reproduction numbers?
These are used to describe the spread of an epidemic and include the effective reproduction number and the basic reproduction number
What is the effective reproduction number? What do its values mean?
The affection reproduction number (R) is the average number of secondary cases of an infectious disease per primary case observed in the population
If the disease is endemic R = 1
At the start of an epidemic R>1
In order to control an infectious disease and lead to a decrease in cases R < 1
Definition of basic reproduction number
The basic reproduction number (R0) is defined as the average number of secondary infections produced when one infected individual is introduced into a host population where everyone is susceptible (i.e. the situation where R would be at its maximum).
This number gives a measure of the infectiousness of the organism independent of how many immune people there are in a population.
An infection will take hold in a population only if R0>1
Why does an R value less than 1 lead to a disease dying out?
Because each generation of infection will have fewer infectious individuals than the previous generation
What is a primary case?
The person that brought the disease into a population
What is a secondary case?
someone who caught the disease from the primary
What is the secondary attack?
The risk of secondary cases among all those people exposed to a primary case. It is often difficult to establish everyone who has been exposed to a primary case. Often it is done in a defined exposure setting e.g. a household.
What is the equation for secondary attack rate in a household?
The number of secondary cases in affected households / total number of household contacts of a primary case
