Introduction to epidemiology
- 1. Introduction to Epidemiology By: Hebatalla Mohamed Aly Lecturer of industrial and occupational medicine
- 2. Lecture outline • What is epidemiology • Scope of epidemiology • Components of epidemiology • Types of epidemiology
- 3. What is epidemiology • The word epidemiology comes from the Greek words epi, meaning on or upon, demos, meaning people, and logos, meaning the study of. • Epidemiology: is often described as the basic science of public health.
- 4. What is epidemiology (cont.) • Epidemiology is the study of the frequency, distribution and determinants of health- related states or events (including disease) among specified population, and the application of this study to the control of diseases and other health problems. • It is the bridge between biomedical, social and behavioral sciences
- 5. What is epidemiology (cont.) • •Systemic collection, analysis and interpretation of data •Includes surveillance, observations, hypothesis testing, analytic research and experiments. Study •Number of times an event occur •Number of affected/study populationFrequency •Pattern: according to time, place and person.Distribution •Not only causes of disease but also all factors that influence the occurrence of disease and other health-related eventsDeterminants •Anything that affects the health and well-being of a populationHealth related states •Those with identifiable characteristics (community).Specified population •Applying the knowledge gained by the studies to community- based practice. Application
- 6. What is epidemiology (cont.) Generally epidemiology answers 6 major questions: how many, who, where, when, why and how???
- 7. What is epidemiology (cont.) • Frequency: answers the question of how many? epidemiology is a quantitative science • Distributions: answers the questions of who, where and when? epidemiology describes health events • Determinants: answers the questions of why and how? epidemiology analyzes health events
- 8. What is epidemiology (cont.) • Health related events: epidemiology not only study diseases but any health related event epidemiology is a broader science • Population: epidemiology diagnose and treat communities/populations not only patients as clinical science epidemiology is a basic science of public health • Application: epidemiology have direct and practical applications for prevention of diseases and promotion of health epidemiology is an applied science
- 9. Scope of epidemiology • Epidemiology was originally focused exclusively on epidemics of communicable diseases • It was subsequently expanded to address endemic communicable diseases and non- communicable infectious diseases. • By the middle of the 20th Century, it was applied to chronic diseases, injuries, birth defects, maternal-child health, occupational health, and environmental health. • Then epidemiologists began to look at behaviors related to health and well-being, such as amount of exercise and seat belt use.
- 10. Types of epidemiology • Epidemiology is classified into 2 broad categories: Descriptive . Concerned with frequency and distribution . Answers how many, who when and where Analytic . Concerned with determinants . Answers how and why
- 11. Purpose of epidemiology 1. To investigate nature / extent of health- related phenomena in the community / identify priorities 2. To study natural history and prognosis of health-related problems 3. To identify causes and risk factors 4. To recommend / assist in application of / evaluate best interventions (preventive and therapeutic measures) 5. To provide foundation for public policy
- 12. Descriptive epidemiology • Disease frequency: The core part of epidemiology is to measure the frequency of diseases, disability or death in a specified population. Ratio: is a comparison between 2 numbers the numerator may or mayn’t be included in the denominator Proportion: is a comparison between 2 numbers but the numerator is included in the denominator Rate: occurrence of an event over time (proportion with added dimension)
- 13. Descriptive epidemiology (cont.) • Rates include: • Assuming pop. Stable, incidence and duration unchanged prevalence = incidence x duration The no. of new cases of a disease that occur during a specified period of time in a population at risk for developing the disease. Incidence The no. of affected persons present in the population at a specific time divided by the number of persons in the population at that time: Prevalence
- 14. Descriptive epidemiology (cont.) • N.B. prevalence may be increased by: Longer duration of disease Prolongation of life without cure Increase of new cases (i.e incidence) In migration of cases Out migration of healthy people In migration of susceptible people Improved diagnostic facilities
- 15. Descriptive epidemiology (cont.) • Disease distribution: Time Place Person
- 16. Time • Changing or stable • Disease trend over time (fluctuation) Long term fluctuation (secular) Periodic fluctuation (seasonal, cyclic) Short term fluctuation (epidemic, outbreak)
- 17. Time • Clustered (epidemic) or evenly distributed (endemic) Endemic - The habitual presence (or usual occurrence) of a disease within a given geographic area Epidemic - The occurrence of an infectious disease clearly in excess of normal expectancy, and generated from a common or propagated source Pandemic - A worldwide epidemic affecting an exceptionally high proportion of the global population
- 18. Place • Geographically restricted or widespread (outbreak, epidemic, pandemic)? Off-shore (tsunami…) • Climate effects (temperature, humidity, combined effects..) • Urban / sub-urban / rural • Relation to environmental exposure (water, food supply, etc) • Multiple clusters or one
- 19. Person • Age • Gender • Socio-economic status (education, occupation, income) • Marital status • Ethnicity/race/genetic profile • Behavior / habits
- 20. Analytic epidemiology • Disease determinants: the questions how and why are answered by the epidemiological triad Agent environmentHost
- 21. Agent • Biological agents Bacteria Viruses Fungi Parasites • Physical agents Heat and cold Radiation Pressure,… • Chemical agents Endogenous Exogenous Dust Toxic gases,.. • Mechanical agents Falling Slipping Hitting
- 22. Host • Genetic susceptibility • Immunologic status • Personal characteristics (age, gender, social class) • Personal behavior and lifestyle • Personal hygiene
- 23. Environment • Living conditions (housing, crowding, water supply, refuse, sewage, etc) • Atmosphere / climate • Mode of communication: (phenomena in the environment that brings host and agent together) • Air quality