Disease Occurence.pptx

Epidemiology

1. Concept of disease occurrence

2. Introduction A critical premise of epidemiology is that disease and other health events do not occur randomly in a population, but are more likely to occur in some members of the population than others because of risk factors that may not be distributed randomly in the population

3. Causation/Cause In epidemiology a cause can be considered to be something that alter the frequency of disease, health and production status or associated factors in population

4. Causation models Many models are present in epidemiology but the most common are Epidemiological triad Wheel or pie model Web model The sufficient cause and component causes model (Rothman’s component cause model)

5. Epidemiological triad Traditional model of infectious disease causation It has three components An external agent Susceptible host Environmental factors These components interrelate in variety of complex ways to produce disease and alter production

6. Agent factors 1. infectious agents- agent might be Mos (virus, bacteria, parasites, prions). Generally these agents must be present for the disease to occur as an essential causal factor . 2. Nutritive- excessive or deficiencies (cholesterol, vitamins and minerals) 3. chemical agents- ( carbon monoxide, drugs and medication) 4. Physical agents- (ionizing radiation, non-ionizing radiation)

7. Agent factors Living organism : adaptability, host range, virulence, pathogenicity, dose ID50, LD50 Chemical agents (toxins n pollutants ): toxicity dose, penetrability, stability, half life Physical agents (radiation, sounds, winds, floods, droughts, soil): composition, magnitude, exposure time

8. Host factors Host factors are intrinsic factors that influence an individual’s exposure, susceptibility or response to causative agent. Host factors that affect an individuals risk of exposure to an agent : age, race, breed, strain, purpose of domestication, feed and feeding habits, breeding practices, sociological status etc. Host factors which affect the susceptibility and response to an agent : genetic composition, nutritional and immunogenic status, anatomic structure, presence of other diseases and medications, purpose and use of domestication, method of rearing and husbandry practices and psychological makeup.

9. Environmental factors These are the extrinsic factors which affect the agent as well as host and opportunity for exposure. Environmental factors include: Physical factors such as geology and climate Biological factors such as insects that transmit an agent Socioeconomic factors such as crowding, sanitation and availability of health services,

10. Web of causation It is devised to address chronic disease and can also be applied to communicable diseases due to multifactorial/multi-etiological nature of causation in many diseases. Silent features There is no single cause Causes of diseases are interacting in various ways Illustrate the interconnections of possible causes Here the disease is usually well-defined from clinical point of view but the etiological perspective is more complex

11. Examples

12. The wheel of disease causation Mausner and Kramer, 1985 The wheel of causation de-emphasizes the agent as the sole cause of disease It emphasizes the interplay of physical, biological and social environments It also brings genetics into the mix A disease model which discriminates between “necessary” and “sufficient” factors

13. Necessary and sufficient causes A necessary cause is a causal factor whose presence is required for the occurrence of the effect. If disease does not develop without the factor being present, then we term the causative factor “ necessary ” Sufficient cause is “ a minimum set of conditions, factors or events needed to produce a given outcome ”. The factors or conditions that form a sufficient cause are called component causes

14. Example

15. Rothman’s component causes and causal pies model Rothman’s model has emphasized that the causes of diseases comprise a collection of factors. These factors represent a pieces of pie, the whole pie(combinations of factors) is the sufficient cause for the disease. May be several pies for a disease or syndrome It shows that disease may have more than one sufficient cause, with each sufficient cause being composed of several factors

16. Rothman’s component causes and causal pies model