Epidemiology
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Epidemiology is the study of disease distribution and determinants in populations. Hippocrates was the first epidemiologist, observing disease contributing factors. Thomas Sydenham classified fevers in London. In the 1700s, Jesty and Jenner observed cowpox conferred smallpox immunity, leading to vaccination. Lind identified scurvy remedies, reducing cases in sailors. Pasteur and Koch proved germ theories of disease. Advances like microscopy helped early epidemiologists understand disease transmission and dynamics.
Epidemiology
- 1. EPIDEMIOLOGY • Greek word – Epi(among) + demos(people) + logos(study) • Epidemiology is defined as “ 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.”
- 2. HISTORY HIPOCRATES • Father of medicine and First epidemiologist. • Wrote 3 books – Epidemic I, Epidemic III and On Airs, Waters and Places. • His teachings about how to observe any and all contributing or causal factors of a disease are still sound epidemiologic concepts.
- 3. THOMAS SYDENHAM • Classified fevers plaguing London in 1660s and 1670s in 3 levels or classes – Continued fevers, Intermittent fevers and Smallpox. • He treated smallpox with bed rest and normal bed covers. The treatment of the time, based on Hippocratic theory, was to use heat and extensive bed coverings. EPIDEMIOLOGY OF COWPOX AND SMALL POX • In mid 1700s, Benjamin Jesty observed that persons exposed to cowpox developed immunity to small pox. • In late 1700s, Edward Jenner invented a vaccination for smallpox. • The late 1960s and early 1970s, Worldwide Global Smallpox Eradication Campaign encouraged vaccination against smallpox and was effective at eliminating this disease. Child infected with Smallpox
- 4. THE EPIDEMIOLOGY OF SCURVY • In 1754, James Lind’s book A Treatise on Scurvy identified the symptoms of scurvy and the fact that the disease became common in sailors after as little as a month at sea. • He conducted an experimental study on scurvy and observed that oranges and lemons were the most effective remedies for scurvy at sea. • As a consequence of Lind’s epidemiologic work, since 1895, the British navy has required that limes of lime juice be included in the diet of seamen, resulting in the nickname of British seamen of “limeys”. Gums bleeding due to Scurvy
- 5. EPIDEMIOLOGIC WORK OF PASTEUR AND KOCH • Pasteur discovered an anthrax vaccine and successfully demonstrated that vaccinations were effective approaches in disease control. • Koch demonstrated that the anthrax bacillus was the only organism that caused anthrax in a susceptible animal. • Koch discovered the tubercle bacillus and cholera bacterium and proved that cholera was transmitted by drinking water, food, and clothing. • Koch also perfected the concept of steam sterilization. • Koch‘s major contribution in epidemiology was a paper on waterborne epidemics and how they can be largely prevented by proper water filtration. Zebra suffering from anthrax
- 6. THE INVENTION OF MICROSCOPE • The microscope first found scientific use in the 1600s through the work of Cornelius Drebbel, the Janssen brothers of the Netherlands and Antoni Van Leeuwenhoek. • Leeuwenhoek was the first to describe the structure of the crystalline lens. • Leeuwenhoek did a morphologic study of red corpuscles in the blood. • Leeuwenhoek saw the connection of arterial circulation to venous circulation in human body through microscopic study of capillary networks.
- 7. Selections from Natural and Political Observations Made Upon the Bills of Mortality by John Graunt (First Edition 1662) DISEASE MORTALITY Abortive and Stillborn 445 Fever 1108 Jaundies 43 Measles 80 Plague 8 Swine Pox 6 Worms 27
- 8. Some definitions related to epidemiology • Incidence is a measure of the probability of occurrence of a given medical condition in a population within a specified period of time. • The term disease broadly refers to any condition that impairs the normal functioning of the body. • For this reason, diseases are associated with dysfunctioning of the body's normal homeostatic process. • The person who is suffering from a disease or disorder is called sick or ill.
- 9. • An infection is said to be endemic in a population when that infection is maintained in the population without the need of external input. • E.g., Chicken pox • Pandemic is an epidemic occurring on a scale which crosses international boundaries usually affecting a large no. of people. • E.g. H1N1 flu, Bird flu • Occurrence of new cases of a certain disease in a given population and during a given period substantially exceeds what is expected based on the recent experience then that disease is known as epidemic. • E.g., Plague epidemic in Gujarat(1994)
- 10. • Epizootic: An epidemic outbreak of disease in an animal population, often with the implication that it may extend to humans. • For example, Rift Valley fever (RVF) primarily affects livestock and can cause disease in a large number of domestic animals -- an "epizootic" -- and the presence of an RVF epizootic can lead to an epidemic among humans who are exposed to diseased animals. • Suddenly and temporarily affecting a large number of animals over a large area Epizootic in medicine • Affecting a large number of animals at the same time within a particular region or geographic area. Used of a disease. Epizootic in science • Adjective Relating to a rapidly spreading disease that affects a large number of animals at the same time within a particular area.
- 11. Morbidity • The proportion of sickness or of a specific disease in a geographical locality. • In medicine • The quality of being morbid. • A diseased state. • The incidence or prevalence of a disease. • Morbidity rate.
- 12. Mortality • The state or condition of being subject to death; mortal character, nature, or existence. • The relative frequency of deaths in a specific population; death rate. • The number of deaths in a given period. In medicine • The quality or condition of being mortal. • Death rate.
- 13. Public health surveillance • Public health surveillance is the ongoing systematic collection, analysis, and interpretation of data, closely integrated with the timely dissemination of these data to those responsible for preventing and controlling disease and injury. • Public health surveillance is a tool to estimate the health status and behaviour of the populations served by ministries of health, ministries of finance, and donors. • Because surveillance can directly measure what is going on in the population. • It is useful both for measuring the need for interventions and for directly measuring the effects of interventions.
- 14. Prevalence • The condition of being prevalent, or widespread: Prevalence in medicine • The total number of cases of a disease in a given population at a specific time.
- 15. The Dynamics of Disease Transmission Diseases can be transcribed directly as well as indirectly. Modes of Disease Transmission 1.Direct a). Person to Person contact 2.Indirect a). Common vehicle 1. Single exposure 2. Multiple exposure 3. Continuous exposure b) Vector
- 16. 1) Human disease do not arise in a vaccum. 2) It results from an interaction of host(a person), agent (e.g a bacterium), and the environment(e.g water supply) • A vector such as mosquito or a deer tick is always involved. 3) But for such interactions to take place humans should be susceptible which is determined by factors like genetic background and nutritional and 4) characteristics.
- 17. The epidemiologic triad of disease