Transcript Measures
Epidemiology With Respect to
the Dynamics of Infectious
Diseases
Huaizhi Chen
Epidemiology
Definition: The study of the causes,
distribution, and control of disease in
populations.
Our goal is to understand its dynamics as
applied to infectious diseases.
Measures
Incidence
Rate of new appearances of an infection or a
disease per unit time.
Examples:
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
Proportion of a population infected at some time.
Examples:
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
Other Measures:
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
Determine whether a disease is seasonal or
random.
Example: Dengue
Measures
Example: Measles, Bubonic Plague
Use of Incidence
Relationship with stratified characteristics of
the sample
Demographics
Age
Sex
Etc.
Use of Incidence
Example: Measles
Use of Incidence
Determination of the relationship between the
transmission and the density of susceptible
individuals within a population.
Serological Survey
Measure of the proportion of the population
with antibodies to specific antigens.
Uses:
Immunity
Lose of Immunity.
Average Age for Immunity.
Serological Survey
Serological Survey
Saturation of Seropositive Population
Lose of immunity in people who obtained it
early in life.