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Epidemiology
 

Epidemiology

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    Epidemiology Epidemiology Presentation Transcript

    • Epidemiology
    • E p id e m io lo g y Comes from Greek words  e p i , meaning “on or upon”  d e m o s ,meaning “people”  l o g o s , meaning “the study of” Study of distribution and determinants of health-related conditions or events in populations
    • History Hippocrates (circa 400 B.C.) attempted to explain disease occurrence from a rational instead of a supernatural viewpoint
    •  John Graunt, a London haberdasher, published his landmark analysis of mortality data in 1662. He was the first to quantify patterns of birth, death, and disease occurrence, noting male-female disparities, high infant mortality, and seasonal variations
    • Mid 1800’s William Farr began to systematically collect and analyze Britain’s mortality statistics. John Snow, an anesthesiologist, conducted a series of investigations in London that later earned him the title “the father of epidemiology.”
    •  discipline did not flourish until the end of the Second World War
    • Uses
    • P o p u la t io n o rc o m m u n it y h e a lt ha s s e s s me nt What are the actual and potential health problems in the community? Where are they? Who is at risk? Which problems are declining over time? Which ones are increasing or have the potential to increase? How do these patterns relate to the level and distribution of services available?
    • T h e E p id e m io lo g icApproa c h C a s e D e f i n i t i o n – a set of standard criteria for deciding whether a person has a particular disease or other health-related condition.
    • Statistics and Reports When physicians diagnose a case of a reportable disease they send a report of the case to their local health department.  Time - when the case occurred  place - where the patient lived  person - the age, race, and sex of the patient
    •  Health departments convert the case counts into r a t e s , which relate the number of cases to the size of the population where they occurred
    • Types of Epidemiology
    • Descriptive Epidemiology organize and summarize data according to time, place, and person  Time – disease rates change over time – the seasonal increase in influenza with the onset of cold weather  time data is usually shown on a graph
    •  Place - describe a health event by place to gain insight into the geographical extent of the problem.  Residence  Birthplace  place of employment  school district  hospital unit, etc
    • Person inherent characteristics of people Age Race Sex
    • Acquired Characteristics Immunity Marital status
    • Activities Occupation Leisure activities Use of medications/tobacco/drugs
    • Conditions under which people live Socioeconomic status Access to medical care
    • Analytic Epidemiology Used to search for causes and effects, or the why and the how.
    • E x p e r im e n t a l determine the exposure status for each individual (clinical trial) or community (community trial); we then follow the individuals or communities to detect the effects of the exposure
    • O b s e r v a t io n a l observe the exposure and outcome status of each study participant  c o h o r t s t u d y - categorize subjects on the basis of their exposure and then observe them to see if they develop the health conditions being studied  c a s e -c o n t r o l study - enroll a group of people with disease (“cases”) and a group without disease (“controls”) and compare their patterns of previous exposures
    • Causation
    •  c a u s e of disease is a factor (characteristic, behavior, event, etc.) that influences the occurrence of disease  An increase in the factors leads to an increase in disease.  Reduction of the factors leads to a reduction in disease
    • E p id e m io lo g ict r ia n g le traditional model of infectious disease causation. Agent Host Environment
    • Ag e nt Infectious microorganism - must be present for disease to occur  Virus  Bacterium Agent  Parasite  other microbe Host Environment
    • Host factors Intrinsic factors that influence an individual’s exposure, susceptibility, or response to a causative agent.  Age Agent  Race  Sex  socioeconomic status  behaviors Host Environment
    • Environmental factors Extrinsic factors which affect the agent and the opportunity for exposure  physical factors  biologic factors Agent  socioeconomic factors Host Environment
    • Epidemiology and Disease
    • Chain of Infection Mode of Transmission Susceptible Reservoir Host Mode of Transmission
    • Chain of Infection r e s e r v o i r of an agent is the habitat in which an infectious agent normally lives, grows, and multiplies. P o r t a l o f e x i t is the path by which an agent leaves the source host
    • Chain of Infection Modes of transmission  Direct – immediate transfer of the agent from a reservoir to a susceptible host by direct contact or droplet spread  Direct contact  Droplet spread  Indirect – an agent is carried from a reservoir to a susceptible host by suspended air particles or by animate (v e c t o r ) or inanimate (v e h i c l e ) intermediaries  Airborne  Vehicleborne  Vectorborne  Mechanical  Biologic
    • Chain of Infection Portal of entry – means by which an agent enters a susceptible host Host – individual infected with the agent
    • Epidemic D i s e a s eO c c urre nc e Level of Disease - amount of a particular disease that is usually present in a community Increasing amount of disease Pandemic Epidemic Endemic Sporatic
    •  Sporadic - irregular pattern of occurrence, with occasional cases occurring at irregular intervals
    •  Endemic - persistent level of occurrence with a low to moderate disease level
    •  Epidemic or Outbreak- occurrence of a disease within an area is clearly in excess of the expected level for a given time period
    •  Pandemic - an epidemic spreads over several countries or continents, affecting a large number of people