Epidemiology With Respect to the Dynamics of Infectious Diseases

Huaizhi Chen

EpidemiologyEpidemiology

Definition: The study of the causes, Definition: The study of the causes, distribution, and control of disease in distribution, and control of disease in populations. populations.

Our goal is to understand its dynamics as Our goal is to understand its dynamics as applied to infectious diseases.applied to infectious diseases.

MeasuresMeasures IncidenceIncidence

Rate of new appearances of an infection or a Rate of new appearances of an infection or a disease per unit time.disease per unit time.

Examples:Examples: Incidence (annual) of Hepatitis A:Incidence (annual) of Hepatitis A: 32,000 new cases 32,000 new cases

in the USA 1992 in the USA 1992 Incidence (annual) of HIV/AIDS:Incidence (annual) of HIV/AIDS: approximately approximately

40,000 annual cases in USA (NIAID) 40,000 annual cases in USA (NIAID)

http://www.wrongdiagnosis.com/h/hiv_aids/prevalence.htmhttp://www.wrongdiagnosis.com/h/hiv_aids/prevalence.htm

MeasuresMeasures

PrevalencePrevalence Proportion of a population infected at some time.Proportion of a population infected at some time. Examples:Examples:

Prevalance of Hepatitis A:Prevalance of Hepatitis A: 32 to 38 percent of U.S. 32 to 38 percent of U.S. population that have any history of disease (1991) population that have any history of disease (1991)

Prevalance:Prevalance: approx 1 in 302 or 0.33% or 900,000 approx 1 in 302 or 0.33% or 900,000 people in USA people in USA

Importance is relative to the disease.Importance is relative to the disease.

http://www.wrongdiagnosis.com/h/hiv_aids/prevalence.htmhttp://www.wrongdiagnosis.com/h/hiv_aids/prevalence.htm

MeasuresMeasures

Other Measures:Other Measures: Related to both incidence and prevalenceRelated to both incidence and prevalence Proportion of the population with antibodies.Proportion of the population with antibodies. Number of deaths.Number of deaths. Etc.Etc.

ExamplesExamples

MeasuresMeasures

Stratified by many characteristics/endogenous Stratified by many characteristics/endogenous variables.variables. Insight can be gain by looking into these Insight can be gain by looking into these

characteristics.characteristics. Availability of measuresAvailability of measures

Report of some diseases is mandatory by general Report of some diseases is mandatory by general practioners.practioners.

Use of IncidenceUse of Incidence

Determine whether a disease is seasonal or Determine whether a disease is seasonal or random.random.

Example: DengueExample: Dengue

Example: Measles, Bubonic PlagueExample: Measles, Bubonic Plague

MeasuresMeasures

Use of IncidenceUse of Incidence

Relationship with stratified characteristics of Relationship with stratified characteristics of the samplethe sample DemographicsDemographics AgeAge SexSex Etc.Etc.

Use of IncidenceUse of IncidenceExample: MeaslesExample: Measles

Use of IncidenceUse of Incidence

Determination of the relationship between the Determination of the relationship between the transmission and the density of susceptible transmission and the density of susceptible individuals within a population.individuals within a population.

Serological SurveySerological Survey

Measure of the proportion of the population Measure of the proportion of the population with antibodies to specific antigens.with antibodies to specific antigens.

Uses:Uses: ImmunityImmunity Lose of Immunity.Lose of Immunity. Average Age for Immunity.Average Age for Immunity.

Serological SurveySerological Survey

Serological SurveySerological Survey

Saturation of Seropositive PopulationSaturation of Seropositive Population Lose of immunity in people who obtained it Lose of immunity in people who obtained it

early in life.early in life.