A Little Bit of History Those who fail to learn from history are doomed to repeat it Winston Churchill 21041437 1 Dr Mohammed Alnaif CHAPTER TWO Classical Epidemiology ID: 915481
Download Presentation The PPT/PDF document "CHAPTER TWO Classical Epidemiology" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
CHAPTER TWOClassical Epidemiology
A Little Bit of History“Those who fail to learn from history are doomed to repeat it”. Winston Churchill
21/04/1437
1
Dr. Mohammed Alnaif
Slide2CHAPTER TWOClassical Epidemiology
A Little Bit of HistoryClassical Epidemiology is concerned with description and hypothesis testing of groups of people.21/04/14372
Dr. Mohammed Alnaif
Slide3CHAPTER TWOClassical Epidemiology
A Little Bit of HistoryJohn Graunt wrote the Bills of Mortality at the end of the seventeenth century.Based on the Bills of Mortality (what we would today call death records) he gathered from parishes in London and Hampshire, Graunt attempted to draw some conclusions about matters of life and death.
.
21/04/1437
3
Dr. Mohammed Alnaif
Slide4CHAPTER TWOClassical Epidemiology
He discovered for example:There were large number of boys born than girlsThe mortality rate increased in the autumn ("the most unhealthful season")"Some
Diseases and Casualties keep a constant proportion whereas some others are very irregular
.”.
21/04/1437
4
Dr. Mohammed Alnaif
Slide5CHAPTER TWOClassical Epidemiology
By looking at changes over time, Graunt was able to identify diseases that increased in mortality.21/04/14375
Dr. Mohammed Alnaif
Slide6CHAPTER TWOClassical Epidemiology
About 150 years later there were two studies of infectious diseases that laid the foundation for classical epidemiology and used methods that are still part of our armamentarium.21/04/14376
Dr. Mohammed Alnaif
Slide7CHAPTER TWOClassical Epidemiology
In 1846 there was an outbreak of measles in the Danish Faroe Islands.The physician, who investigated the epidemic Peter Ludwig Panum, determined:That there is a delay between the time of exposure and the development of the rash (Incubation Period).
21/04/1437
7Dr. Mohammed Alnaif
Slide8CHAPTER TWOClassical Epidemiology
That the disease is transmitted by direct contact between infected and susceptible people and does not arise spontaneously or because of "miasma”When people with the disease were infectious
Most importantly that previous about of measles protected people from subsequent attacks.
21/04/1437
8
Dr. Mohammed Alnaif
Slide9CHAPTER TWOClassical Epidemiology
Approximately 10 years later, John Snow investigated the cause of the increased rate of cholera in London. He observed that the disease was most prevalent in districts supplied with water by certain companies that obtained there water from a section of Thames River that was extremely polluted with sewage.21/04/1437
9
Dr. Mohammed Alnaif
Slide10CHAPTER TWOClassical Epidemiology
He also noted that the rate of new cases of cholera declined in those households supplied by the Lambeth Company after it relocated its intake pipe to a less polluted part of the Thames River.21/04/143710
Dr. Mohammed Alnaif
Slide11CHAPTER TWOClassical Epidemiology
At the same time there was no change in the incidence of the disease in homes supplied by other companies that continued to draw its water from the heavily polluted section of the river.21/04/143711
Dr. Mohammed Alnaif
Slide12CHAPTER TWOClassical Epidemiology
Some Basic ConceptsPerhaps the worst epidemic to ever inflict humanity was the outbreak of bubonic plague, or the Black Death, that swept through Europe in the middle of the fourteenth century.21/04/1437
12
Dr. Mohammed Alnaif
Slide13CHAPTER TWOClassical Epidemiology
Some Basic ConceptsAlthough precise figures on the number of deaths are almost impossible to determine, it has estimated that one quarter to one third of the population of Europe, or 15 to 20 million people died.21/04/1437
13
Dr. Mohammed Alnaif
Slide14CHAPTER TWOClassical Epidemiology
Some Basic ConceptsYet as terrible as these figures are, two points are readily apparent.First, not everyone was affected. Even in Florence, Italy, the death rate was nearly 70 percent, but of course 30 percent of the populace was not affected.
21/04/1437
14Dr. Mohammed Alnaif
Slide15CHAPTER TWOClassical Epidemiology
Some Basic ConceptsYet as terrible as these figures are, two points are readily apparent.Second, the plague was not always present. It came in waves during a period of few years, disappearing in the winter and reappearing in the spring, until it finally faded from the scene.
21/04/1437
15Dr. Mohammed Alnaif
Slide16CHAPTER TWOClassical Epidemiology
Some Basic ConceptsThe question this raises is why Why some people and not others,
Why in 1347 and not the previous year,
Why in the warm moths but not winter,
Why
humans and not dogs, and on and on
.
21/04/1437
16
Dr. Mohammed Alnaif
Slide17CHAPTER TWOClassical Epidemiology
Some Basic ConceptsLet's take a look at some of the factors that might provide an explanation for some of these questions by using the plague and other disorders as modelsAgent, Person, Place, and Time.
21/04/1437
17
Dr. Mohammed Alnaif
Slide18CHAPTER TWOClassical Epidemiology
Agent, It seems as if every time we open the newspaper, or watch TV we're greeted with news that something else is going to kill us. There are only certain things that are necessary etiologic factors for diseases- what epidemiologist call AGENT
.
21/04/1437
18
Dr. Mohammed Alnaif
Slide19CHAPTER TWOClassical Epidemiology
Agent, Lilienfeld groups agents into four categories:Nutritive agentsChemical agents
Physical agents
Infectious agents.
21/04/1437
19
Dr. Mohammed Alnaif
Slide20CHAPTER TWOClassical Epidemiology
Nutritive agentsSome nutritive agents can cause disease by an excess of them and others by deficiency.Too much cholesterol, for example may lead to coronary heart disease; too much salt may lead to hypertension; too much calcium may lead to kidney stones.On the other hand too little calcium can lead to osteoporosis.
21/04/1437
20
Dr. Mohammed Alnaif
Slide21CHAPTER TWOClassical Epidemiology
Chemical agentsChemical agents may consist of allergens, Example paint, cleaning agents, various food dyes; or poison, Example arsenic, carbon monoxide, overdose of tricyclic antidepressant.
21/04/1437
21Dr. Mohammed Alnaif
Slide22CHAPTER TWOClassical Epidemiology
Physical agentsIonizing radiation or ultraviolet light would be considered among the physical agents that can lead to health problems.21/04/1437
22
Dr. Mohammed Alnaif
Slide23CHAPTER TWOClassical Epidemiology
Infectious agentsPerhaps the most well-known agents to health workers are infectious agents such as viruses (mumps, measles, Ebola virus and acquired immunodeficiency syndrome [AIDS]), bacteria (tuberculosis [TB], rheumatic fever, and syphilis), protozoa (malaria), or rickettsia (typhus, rocky mounting spotted fever).
21/04/1437
23
Dr. Mohammed Alnaif
Slide24Agents
Nutrients
Poisons
Allergens
Radiation
Physical trauma
Microbes
Psychological experiences
CHAPTER TWO
Classical Epidemiology
21/04/1437
Dr. Mohammed Alnaif
24
Slide25CHAPTER TWOClassical Epidemiology
PersonAgents are necessary to cause disease but they are not sufficient. Not everyone who is stung by a bee develops an anaphylactic reaction, and two people could be enjoy the same meal in ALBataha but only one may spend the rest of the night in the emergency room.21/04/1437
25
Dr. Mohammed Alnaif
Slide26CHAPTER TWOClassical Epidemiology
PersonAge
Socio-economic status
Gender
Ethnicity/Race
Behavior
21/04/1437
26
Dr. Mohammed Alnaif
Slide27CHAPTER TWOClassical Epidemiology
person or host factors
Genetic endowment
Immunologic state
Age
Personal behavior
21/04/1437
27
Dr. Mohammed Alnaif
Slide28CHAPTER TWOClassical Epidemiology
PersonIt is obvious that people differ in terms of their susceptibility or response to the agents; this is what we call person or host factors.21/04/1437
28
Dr. Mohammed Alnaif
Slide29CHAPTER TWOClassical Epidemiology
PersonYear of birth is somewhat different from age although the two are obviously related; your year of birth will put you in a birth cohort. What you and your birth cohort experience is determined in part by when you were born.
21/04/1437
29
Dr. Mohammed Alnaif
Slide30CHAPTER TWOClassical Epidemiology
PersonOther host factors are modified or acquired with time, such as age itself and immunologic experience, whether achieved naturally through prior exposure, or artificially through inoculation.
21/04/1437
30
Dr. Mohammed Alnaif
Slide31CHAPTER TWOClassical Epidemiology
PersonA third class of person factors is more transitory, like time-limited comorbid conditions, fatigue, or nutritional status. Such factors affect the person ability to survive an illness.21/04/1437
31
Dr. Mohammed Alnaif
Slide32CHAPTER TWOClassical Epidemiology
PersonFinally, some host factors depend on our behavior – what we call lifestyle whether we exercise, how we make use of health services, what we eat, and so on
.
21/04/1437
32
Dr. Mohammed Alnaif
Slide33CHAPTER TWOClassical Epidemiology
PlaceGeographically restricted or widespread (pandemic
)?
Relation to water or food supply.
Multiple clusters or one?
.
21/04/1437
33
Dr. Mohammed Alnaif
Slide34CHAPTER TWOClassical Epidemiology
PlaceIt is obvious that place, which is also referred to as environment, is rarely a direct factor in its own right. Rather, it reflects a host of other factors that are distributed geographically.
21/04/1437
34
Dr. Mohammed Alnaif
Slide35Environment
Crowding
Atmosphere
Modes of communication
– phenomena in the environment that
bring host and agent together
, such as:
Vector
Vehicle
Reservoir
CHAPTER TWO
Classical
Epidemiology
21/04/1437
Dr. Mohammed Alnaif
35
Slide36CHAPTER TWOClassical Epidemiology
PlaceThese factors include(1) Climate (2) Diet (3) Cultural practices(4) Methods of food preparation and storage(5) Population density (6) Exposure to
pollutants (7) The presence of arthropods that carry disease.
21/04/1437
36
Dr. Mohammed Alnaif
Slide37CHAPTER TWOClassical Epidemiology
PlaceThe challenge to epidemiologist is, once having found differences in the prevalence of some disorder from one place to another, to discover what it is about the environment that gives rise to these variations.21/04/1437
37
Dr. Mohammed Alnaif
Slide38CHAPTER TWOClassical Epidemiology
TimeChanging or stable?
Seasonal
variation
.
Clustered (
epidemic
)
or evenly distributed
(
endemic
)?
Point source or propagated.
21/04/1437
38
Dr. Mohammed Alnaif
Slide39CHAPTER TWOClassical Epidemiology
TimeVariations in the time and occurrence of a particular disease or condition can suggest casual relationships among variables (obviously, this overlaps with year of birth in some cases.21/04/1437
39
Dr. Mohammed Alnaif
Slide40CHAPTER TWOClassical Epidemiology
TimeThe influence of time can also be seen in disorders that occur cyclically or seasonally, example infectious diseases such as the flu.21/04/1437
40
Dr. Mohammed Alnaif
Slide41CHAPTER TWOClassical Epidemiology
SOME OTHER TERMS YOU SHOULD KNOWAn epidemic refers to the outbreak of a disease in a localized group of people. It can be infectious and spread from person to another by:Carrier
, people who are susceptible to the disease, although they may not be affected by it themselves.
Vector, intermediate organisms that carry the disease but do not have it, such as the anopheles mosquito for malaria or fleas for the plague
.
21/04/1437
41
Dr. Mohammed Alnaif
Slide42CHAPTER TWOClassical Epidemiology
SOME OTHER TERMS YOU SHOULD KNOWAn epidemic can also be caused by the sudden introduction of some pathogen.Epidemics
are usually limited in time, although the time can be long as we are seeing in the case of AIDS.
21/04/1437
42
Dr. Mohammed Alnaif
Slide43CHAPTER TWOClassical Epidemiology
SOME OTHER TERMS YOU SHOULD KNOWAn endemic disease is said to be present if cases are continually occurring in some region, for example the presence of river blindness or malaria in certain parts of Africa.
21/04/1437
43
Dr. Mohammed Alnaif
Slide44CHAPTER TWOClassical Epidemiology
SOME OTHER TERMS YOU SHOULD KNOWWhen an epidemic escapes its local region and starts to affect people over a large portion of country or even the world, it said to be pandemic.In this regard, the bubonic plague of the fourteenth century would more properly be called a pandemic
rather than an epidemic.
21/04/1437
44
Dr. Mohammed Alnaif
Slide45Thank You21/04/1437
45Dr. Mohammed Alnaif