Glossary |
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Below are some of the key terms used in Epidemiology and in this manual: Asymptomatic |
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Asymptomatic: Individuals who have been infected
but who do not yet show any signs of the disease.
Birth rate: The number of births per individual in the
population during a specified time interval.
Contact Rate: The average number of contacts that an
individual makes during a given time period, per 1000 individuals in the population.
Note that these are contacts that allow transmission of a particular disease. Hence
for an airborne disease, the contact rate would be much higher than for a sexually-transmitted
or blood-borne disease. [Also note that in the model used in JAVA Epidemiology
1.0, the contact rate is density-dependent.]
Death Rate: The fraction of the population that dies
during a specified time interval.
Density dependent: A factor that changes values depending
on the density of the host population. In Epidemiology, the user may set the
contact rate (average number of contacts per individual per time interval) to be
density-dependent or density-independent.
Disease Death Rate: The fraction of the population
that dies during a specified time due to the disease.
Duration of infection -- This is the average number
of time units that an individual remains infected before moving into the recovered
category (provided, of course, that he/she doesn't die!).
Immunity Loss: A measure of the rate at which individuals
who have recovered from the disease or who have been immunized lose their immunity
and become susceptible to infection again. In age-structured models, this rate can
depend on age.
Immunization rate -- This is the proportion of
newborns that are vaccinated. Right now, the program makes the unrealistic assumption
that vaccinated individuals remain immune for life. To start out, set this to 0.
Isolation Response: A measure of how the proportion
of individuals in the population that show symptoms of a disease influences the contact
rate (average number of contacts per individual per time interval). A positive isolation
response means that the contact rate decreases as the percentage symptomatic increases.
The higher the isolation response, the more rapid the decrease.
Latent: Individuals are in a latent state when they have
been infected, but are not yet showing symptoms, and are not yet infectious.
Natural (or Background) Death Rate: The fraction of
the population that dies during a specified time interval due to causes other
than the disease.
Probability of transmission: The probability that
a susceptible individual will become infected in a particular contact with an infectious
individual. This value must be between zero and one.
Recovery Rate: The rate at which infected individuals
recover from the infection and become immune. In age-structured models, this rate
can depend on age.
Symptomatic: Infected individuals who show signs
of having the disease.
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