Epidemiology

Classically speaking Epi = upon (among) Demos = people Ology = science Epidemiology = the science which deals with what falls upon people…..

A Modern Definition “The study of the distribution and determinants of health-related states in specified populations, and the application of this study to control health problems." (Last J) Search for knowledge Apply in health service

Objectives of Epidemiology 1. To describe the distribution and magnitude of health and disease problems in the population. 2. To identify the etiological factors – risk factors in the population. 3. To provide the data essential to planning, implementation and evaluation of services for prevention, control and treatment of disease and to setting up of priorities for these services.

The ultimate aim of epidemiology is to eliminate or reduce health problem or its consequences and to promote health and well-being of society as a whole.

Purposes 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

Component: Disease Frequency- Rate and Ratio e.g Rate- incidence rate, prevalence rate etc Ratio- sex ratio, doctor-population ratio Distribution of Disease- Disease in community find causative factor Generate hypothesis Descriptive epidimiology

Determinants of Disease- To test hypothesis Analytic epidemiology Help in develop sound scientific program

Incidence Number of new cases of a disease which come into being during a specified period of time. (Number of new cases of specific disease during a given period)/(population at risk during that period) x 1000 Importance: If incidence increasing, it may indicate failure or ineffectiveness of control measure of a disease and need for better/new health control measure.

Prevalence Number of current case (old and new) of a specified disease at a point of time It help to estimate the burden of disease Identify potentially high-risk populations. They are essentially helpful to plan rehabilitation facilities, manpower needs, etc. (Number of current case of a specified disease at a point of time)/(estimated population at the same point of time) x 100 Point prevalence AND Period prevalence

Relationship between incidence and prevalence Prevalence =Incidence x Duration

Approach of an epidemiologist Asking questions making comparisons ● Asking questions may provide clues to cause or aetiology of disease e.g. What is the event, what is its magnitude, where did it happen, when did it happen, who were affected, why did it happen?

Making comparisons will help draw inferences to support asking questions. This comparison may be: ● Between those with the disease and those without the disease; ● Those with risk factor and those not exposed to risk factor;

Terms to know Endemic: constant presence of a disease in a given population epidemic: outbreak or occurrence of one specific disease from a single source, in a group population, community, or geographical area, in excess of the usual level of expectancy pandemic: epidemic that is widespread across a country, or large population, possible worldwide

Host Agent Environment Three essential characteristics that are examined to study the cause(s) for disease in analytic epidemiology are...

Host Factors Behaviors Genetic predisposition Immunologic factors Influence the chance for disease or its severity

Agents Biological Physical Chemical Necessary for disease to occur

Environment External conditions Contribute to the disease process

Epidemics arise when host, agent, and environmental factors are not in balance Due to new agent Due to change in existing agent (infectivity, pathogenicity, virulence) Due to change in number of susceptibles in the population Due to environmental changes that affect transmission of the agent or growth of the agent

EPIDEMIOLOGICAL METHODS. The methods he employs can be classified as: 1. Observational studies a. Descriptive studies b. Analytical studies – Case control studies – Cohort studies 2. Experimental/interventional studies – Randomized control studies – Field trials – Community trials

Descriptive Studies Steps in conducting a descriptive study. Descriptive studies form the first step in any process of investigation. These studies are concerned with observing the distribution of disease in populations. 1. Defining the population. 2. Defining disease under study. 3. Describing the disease. 4. Measurement of disease 5. Compare 6. Formulate hypothesis-

Defining the population. Defined population may be the whole population or a representative sample. It can also be specially selected group such as age and sex groups, occupational groups, hospital patients, school children, small community, etc.

2. Defining disease under study. 3. Describing the disease. Disease is examined by the epidemiologist by asking three questions: ● When is the disease occurring—time distribution? ● Where is it occurring—place distribution? ● Who is getting the disease—person distribution?

A. Time Distribution Short-term fluctuations. Epidemic Common source epidemics - single exposure/point source—bhopal tragedy Propagated-infectious - Periodic fluctuations; Seasonal –measles (early spring) cyclic-,, in pre-vaccinated era (peak 2- 3 yr) Long-term or secular trends; diabetes, CVD

B. Place Distribution International variations: Cancer of stomach very common in Japan less common in US. oral cancer- India Breast cancer- Low-japan, high-western National variations, e.g. Distribution of fluorosis,

Rural-urban differences, e.g. CVD, Mental illness more common in urban areas. Skin diseases, worm infestations more common in rural areas. Local distributions, e.g. Spot maps- John Snow in London to incriminate water supply as cause of cholera transmission in London.

cholera cases in proximity to water pump, 1854

C. Person Distribution Age: e.g. Measles is common in children, Cancer in middle age Degenerative diseases in old age. Sex: Women- Lung cancer-less Hyperthyroidism- more c. Social class- Diabetes, Hypertenson– upper class

4. Measurement of disease- Mortality/ Morbidity 5. Compare- Between different population, subgroups 6. Formulate hypothesis. On basis of all data epidemiologist form hypothesis.