Download Measures

Epidemiology With Respect to
the Dynamics of Infectious
Diseases
Huaizhi Chen
Epidemiology
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Definition: The study of the causes,
distribution, and control of disease in
populations.
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Our goal is to understand its dynamics as
applied to infectious diseases.
Measures
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Incidence
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
Rate of new appearances of an infection or a
disease per unit time.
Examples:
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Incidence (annual) of Hepatitis A: 32,000 new cases
in the USA 1992
Incidence (annual) of HIV/AIDS: approximately
40,000 annual cases in USA (NIAID)
http://www.wrongdiagnosis.com/h/hiv_aids/prevalence.htm
Measures

Prevalence
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Proportion of a population infected at some time.
Examples:
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Prevalance of Hepatitis A: 32 to 38 percent of U.S.
population that have any history of disease (1991)
Prevalance: approx 1 in 302 or 0.33% or 900,000
people in USA
Importance is relative to the disease.

http://www.wrongdiagnosis.com/h/hiv_aids/prevalence.htm
Measures
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Other Measures:
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Related to both incidence and prevalence
Proportion of the population with antibodies.
Number of deaths.
Etc.
Examples
Measures

Stratified by many characteristics/endogenous
variables.


Insight can be gain by looking into these
characteristics.
Availability of measures

Report of some diseases is mandatory by general
practioners.
Use of Incidence
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Determine whether a disease is seasonal or
random.
Example: Dengue
Measures

Example: Measles, Bubonic Plague
Use of Incidence
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Relationship with stratified characteristics of
the sample
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Demographics
Age
Sex
Etc.
Use of Incidence

Example: Measles
Use of Incidence
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Determination of the relationship between the
transmission and the density of susceptible
individuals within a population.
Serological Survey

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Measure of the proportion of the population
with antibodies to specific antigens.
Uses:

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Immunity
Lose of Immunity.
Average Age for Immunity.
Serological Survey
Serological Survey
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Saturation of Seropositive Population
Lose of immunity in people who obtained it
early in life.