What is epidemiology?
The study of health and illness in populations.
What is endemic?
Disease occurring at an expected frequency within a population
Geographical distribution of disease
What is an epidemic?
The occurrence of disease at higher than expected frequency. Can be a disease not normally present or occurring at higher than endemic levels.
Do not have to involve large numbers of cases
What is a pandemic?
When an epidemic spreads to multiple continents
New variant of the flu virus appears and spreads pandemically.
Rate of transmission
average number of secondary cases that are caused by exposure to an infected individual
Rate > 1.0 = outbreak expanding
Rate <1.0 = peak is past and outbreak dying out
What is the incubation period?
A period between becoming infected and the onset of symptoms.
The pathogen is multiplying and invading its target tissue but remains at low enough levels disease symptoms are not apparent
What is the infectious period?
The period during which the infected can infect others.
Pathogen levels become high enough for transmission before disease symptoms appear.
What determines rate of transmission?
density and the proportion of members susceptible to the disease
The ability of a population to resist serious epidemics because the majority of its population is immune.
This is the goal of vaccination programs