Introduction to Epidemiology & Distribution of Disease

1. Introduction to Epidemiology& Distribution of Disease Ma Jinxiang, M.S. Department of preventive medicine, Guangzhou medical college • 1021311

2. Introduction to epidemiology • Definition of epidemiology • A brief history of epidemiology • Approaches in epidemiological study • Objectives of epidemiology • Future and challenge of epidemiology Distribution of disease • Description of distribution(time, person and place) • Patterns of epidemic • Measures of disease frequency

3. Epidemiology Definition • epi: • Greek root, epi, over, on • - dem: • Greek root deme, meaning a township, or division, of ancient Attica; whence demos, for people • -logy: • Contemporary English, a branch of learning

4. Epidemiology Definition • Epidemic - ‘all over the people’ • Epidemiology • A branch of learning that deals with events or conditions that are ‘all over the people’ • A branch of medicine that deals with the cause, distribution, and control of disease in populations (American Heritage Dictionary of the English Language, third edition)

5. Epidemiology: Definitions Definition Epidemiologyis the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to control of health problems. Last ed. Dictionary of Epidemiology

6. A brief history of epidemiology——the rudimentary or beginning stage History • Hippocrates – (460-377B.C) • Association between external environment and personal characteristics and health • “Epidemic” firstly appeared in his book –“On airs, waters and places” • John Graunt – 1662 • ‘Bills of Mortality’, a comparative study of morbidity and mortality in human populations

7. History A brief history of epidemiology——the rudimentary or beginning stage • 1747 - Lind performed first ‘experiment’ to establish cause and treatment of scurvy • 1768 - Jenner first vaccinated human with cowpox

8. A brief history of epidemiology——the establish stage of epidemiology as a branch of study History • 1850 - London Epidemiologic Society established by William Farr and colleagues • 1854 - Snow’s investigation of cholera outbreak in London • Father of modern epidemiology • Plotted geography • Established modern epidemiologic methods

9. A brief history of epidemiology——the development stage of epidemiology History • 1945 - Fundamental shift in paradigm after World War II to study chronic diseases • 1948 - Framingham cohort study begun to study coronary artery disease • 1958 - Doll and Hill apply case-control study design to establish smoking as cause of lung cancer • 1980 - DNA fingerprinting, Micro-computing industry begins • 1982 - AIDS epidemic recognized in US, Cox proportional hazards regression analysis

10. History A brief history of epidemiology——epidemiology in china • Wu Lien-teh was considered as pioneer and founder in the history of epidemiology in china.

11. approaches Approaches in Epidemiological studies Cross-sectional study Descriptive study Observational study Ecological study Case-control study Analytical study Cohort study Clinical trial Experimental study Community field trial Theoretical study

12. scope The scope and objectives of Epidemiology • To determine the etiology or cause of a disease, including risk factors • To determine the frequency and extent of health conditions and disease in the community • To study the natural history and applied to diagnosis, treatment and prognosis of disease • To provide the foundation for developing public policy and regulatory decisions relating to health • To prevent and control of disease

13. Epidemiology: Future • Molecular biology will revolutionize the way epidemiologists evaluate gene-environment interaction • Micro-computing will become more sophisticated and more widely available • Biomedical science will make significant advances that will require evaluation of findings in populations • Eco-epidemiology era – 21st century

14. Challenges of Modern Medicine • Behavioral aspects of health • Promotion of healthy lifestyles • Diet • Exercise • Tobacco, alcohol, drugs • Sexual behavior • Management of stress • New diseases – AIDS, SARS, West Nile Virus, bio-terrorism

15. Distribution of disease Short-term/Rapid fluctuation, Seasonal, cyclic/periodicity,secular Temporal (Time) Person Spatial (place) Qualitative measurements (three patterns of distribution) Age,sex,occupation,race/ethnicity,behavior,education,marital status International comparison, regional difference within a country, city/rural,endemic Sporadic, epidemic, pandemic Quantitative measurements Measures of disease frequency

16. Three patterns of distribution Time, place and person • Time characteristics We usually show time data as graph • Short-term/rapid fluctuation (outbreak and epidemic) • Seasonality • Cyclicity/periodicity • Secular/long-term trends

17. Three patterns of distribution Time, place and person • Person characteristics • Age • Sex • Ethnic and racial groups • Behavior

18. Three patterns of distribution Time, place and person • Place characteristics • International comparison • Regional difference within a country • Urban/rural • Endemic

19. Three patterns of distribution Time, place and person • Integrated description of time, person and place • Migrant epidemiology • Birth cohort study

20. Patterns of epidemic • Sporadic– • Is one that occurs only occasionally in population. Occurring upon occasion or in a scattered, isolated or seemingly random way.

21. Patterns of epidemic • Epidemic– • is the occurrence of more cases of disease than would normally be expected in a specific place or group of people over a given period of time. • Pandemic– • is an epidemic that becomes very widespread and affects a whole region, a continent, or the world. For example, AIDS is now pandemic in Africa. • outbreak– • A cluster that is unexplained, often used interchangeably with epidemic

22. Measures of disease frequency • Ratio • Proportion • Rate What, who is in the denominator ? ???

23. Measures of disease frequency Measures of disease occurence(1) • Epidemiology : • « Study of the occurrence of illness » • Two types of measures : • Prevalence • Measures population disease status • Incidence • Assess frequency of disease onset

24. Measures of disease frequency

25. Measures of disease frequency Prevalence Number of cases of disease(old and new) at a specific time Population exposed at that time • Example of bilharziasis in Guadeloupe in 1979: • Population 350,000 • Cases 96,200 • Prevalence 27.6%

26. Measures of disease frequency

27. Incidence Number of NEWcases of disease during a period Population exposed during this period • Incidence Proportion (cumulative incidence), express the probability or risk of illness • Example of bilharziasis in Guadeloupe in 1979: • Population 350,000 • New cases 1,250 • Cumulative incidence 3.6/1000 per year • Prevalence 27.6%

28. Measures of disease frequency Attack Rate • Cumulative incidence during an outbreak • Usually expressed for the entire epidemic period, from the first to the last case • Ex: Outbreak of cholera in country X in March 1999 • Number of cases = 490 • Population at risk = 18,600 • Attack rate = 2.6%

29. Incidence Deaths, Cured, Lost... Measures of disease frequency Relationship between Incidence, Prevalence and Disease Duration Prevalence Duration Merci à Jean-Luc Grenier - CEPIQ98

30. 10 9 8 7 6 5 4 3 2 1 0 Jan Feb Mar Apr May Jun Jul Measures of disease frequency Examples Ratio males/women=8/2 Prevalence March1 =3/10 Proportion of women=2/10=20% Prevalence March-July =7/10 Incidence March-July =4/7

31. Measures of disease frequency • Infection rate • The incidence rate of manifest plus inapparent infections (the latter determined by seroepidemiology). See also attack rate. • Secondary attack rate • The number of cases of an infection that occur among contacts within the incubation period following exposure to a primary case in relation to the total number of exposed contacts. See also attack rate.

32. Crude Mortality Rate Cause-Specific Mortality Rate = = X 100,000 X 100,000 Deaths attributed to a specific cause # of deaths between birth and one year of age Total number of deaths mid-interval Population # of live births during the same time interval Population Measures of disease frequency Measures of disease mortality X 100,000 Infant mortality Rate =

33. = Case fatality Ratio = X 100 X 100,000 Deaths attributed to a specific cause Deaths from all causes number of deaths from a certain disease Number of cases of that disease occurring within the same specified time period Measures of disease frequency Proportionate Mortality

34. Survival rate The percentage of people in a study or treatment group who are alive for a given period of time after diagnosis. This is commonly expressed as 5-year survival Measures of disease frequency

35. Homework: 1, Definition of epidemiology 2, Methods in epidemiological study and their difference 3, Definition of distribution of disease and how to describe time, person and place. 4, Patterns of epidemic (sporadic, epidemic, outbreak and pandemic) 5, Difference between prevalence and incidence 6, Difference between mortality rate and case fatality ratio 7, the association between prevalence, incidence and duration of disease