1. Epidemiology With Respect to the Dynamics of Infectious Diseases Huaizhi Chen

2. Epidemiology Definition: The study of the causes, distribution, and control of disease in populations. 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. Our goal is to understand its dynamics as applied to infectious diseases.

3. Measures Incidence Incidence Rate of new appearances of an infection or a disease per unit time. Rate of new appearances of an infection or a disease per unit time. Examples: Examples: Incidence (annual) of Hepatitis A: 32,000 new cases in the USA 1992 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) Incidence (annual) of HIV/AIDS: approximately 40,000 annual cases in USA (NIAID) http://www.wrongdiagnosis.com/h/hiv_aids/prevalence.htm http://www.wrongdiagnosis.com/h/hiv_aids/prevalence.htm

4. Measures Prevalence Prevalence Proportion of a population infected at some time. Proportion of a population infected at some time. Examples: Examples: Prevalance of Hepatitis A: 32 to 38 percent of U.S. population that have any history of disease (1991) 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 Prevalance: approx 1 in 302 or 0.33% or 900,000 people in USA Importance is relative to the disease. Importance is relative to the disease. http://www.wrongdiagnosis.com/h/hiv_aids/prevalence.htm http://www.wrongdiagnosis.com/h/hiv_aids/prevalence.htm

5. Measures Other Measures: Other Measures: Related to both incidence and prevalence Related 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.

6. Examples

7. Measures Stratified by many characteristics/endogenous variables. Stratified by many characteristics/endogenous variables. Insight can be gain by looking into these characteristics. Insight can be gain by looking into these characteristics. Availability of measures Availability of measures Report of some diseases is mandatory by general practioners. Report of some diseases is mandatory by general practioners.

8. Use of Incidence Determine whether a disease is seasonal or random. Determine whether a disease is seasonal or random. Example: Dengue Example: Dengue

9. Example: Measles, Bubonic Plague Example: Measles, Bubonic Plague Measures

10. Use of Incidence Relationship with stratified characteristics of the sample Relationship with stratified characteristics of the sample Demographics Demographics Age Age Sex Sex Etc. Etc.

11. Use of Incidence Example: Measles Example: Measles

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

13. Serological Survey Measure of the proportion of the population with antibodies to specific antigens. Measure of the proportion of the population with antibodies to specific antigens. Uses: Uses: Immunity Immunity Lose of Immunity. Lose of Immunity. Average Age for Immunity. Average Age for Immunity.

14. Serological Survey

15. Saturation of Seropositive Population Saturation of Seropositive Population Lose of immunity in people who obtained it early in life. Lose of immunity in people who obtained it early in life.