CHAPTER TWO Classical Epidemiology A Little Bit of

CHAPTER TWO Classical Epidemiology A Little Bit of History “Those who fail to learn from history are doomed to repeat it”. Winston Churchill 23/03/42 Dr. Mohammed Alnaif 1

CHAPTER TWO Classical Epidemiology A Little Bit of History Classical Epidemiology is concerned with description and hypothesis testing of groups of people. 23/03/42 Dr. Mohammed Alnaif 2

CHAPTER TWO Classical Epidemiology A Little Bit of History John 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. . 23/03/42 Dr. Mohammed Alnaif 3

CHAPTER TWO Classical Epidemiology He discovered for example: 1. There were large number of boys born than girls 2. The mortality rate increased in the autumn ("the most unhealthful season") 3. "Some Diseases and Casualties keep a constant proportion whereas some others are very irregular. ” . 23/03/42 Dr. Mohammed Alnaif 4

CHAPTER TWO Classical Epidemiology By looking at changes over time, Graunt was able to identify diseases that increased in mortality. 23/03/42 Dr. Mohammed Alnaif 5

CHAPTER TWO Classical 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. 23/03/42 Dr. Mohammed Alnaif 6

CHAPTER TWO Classical Epidemiology In 1846 there was an outbreak of measles in the Danish Faroe Islands. The physician, who investigated the epidemic Peter Ludwig Panum, determined: 1. That there is a delay between the time of exposure and the development of the rash (Incubation Period). 23/03/42 Dr. Mohammed Alnaif 7

CHAPTER TWO Classical Epidemiology 2. That the disease is transmitted by direct contact between infected and susceptible people and does not arise spontaneously or because of "miasma” 3. When people with the disease were infectious 4. Most importantly that previous about of measles protected people from subsequent attacks. 23/03/42 Dr. Mohammed Alnaif 8

CHAPTER TWO Classical 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. 23/03/42 Dr. Mohammed Alnaif 9

CHAPTER TWO Classical 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. 23/03/42 Dr. Mohammed Alnaif 10

CHAPTER TWO Classical 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. 23/03/42 Dr. Mohammed Alnaif 11

CHAPTER TWO Classical Epidemiology Some Basic Concepts Perhaps 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. 23/03/42 Dr. Mohammed Alnaif 12

CHAPTER TWO Classical Epidemiology Some Basic Concepts Although 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. 23/03/42 Dr. Mohammed Alnaif 13

CHAPTER TWO Classical Epidemiology Some Basic Concepts Yet 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. 23/03/42 Dr. Mohammed Alnaif 14

CHAPTER TWO Classical Epidemiology Some Basic Concepts Yet 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. 23/03/42 Dr. Mohammed Alnaif 15

CHAPTER TWO Classical Epidemiology Some Basic Concepts The question this raises is why v Why some people and not others, v Why in 1347 and not the previous year, v Why in the warm moths but not winter, v Why humans and not dogs, and on. 23/03/42 Dr. Mohammed Alnaif 16

CHAPTER TWO Classical Epidemiology Some Basic Concepts Let'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 models Agent, Person, Place, and Time. 23/03/42 Dr. Mohammed Alnaif 17

CHAPTER TWO Classical 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. 23/03/42 Dr. Mohammed Alnaif 18

CHAPTER TWO Classical Epidemiology Agent, Lilienfeld groups agents into four categories: 1. Nutritive agents 2. Chemical agents 3. Physical agents 4. Infectious agents. 23/03/42 Dr. Mohammed Alnaif 19

CHAPTER TWO Classical Epidemiology Nutritive agents Some 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. 23/03/42 Dr. Mohammed Alnaif 20

CHAPTER TWO Classical Epidemiology Chemical agents may consist of allergens, Example paint, cleaning agents, various food dyes; or poison, Example arsenic, carbon monoxide, overdose of tricyclic antidepressant. 23/03/42 Dr. Mohammed Alnaif 21

CHAPTER TWO Classical Epidemiology Physical agents Ionizing radiation or ultraviolet light would be considered among the physical agents that can lead to health problems. 23/03/42 Dr. Mohammed Alnaif 22

CHAPTER TWO Classical Epidemiology Infectious agents Perhaps 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). 23/03/42 Dr. Mohammed Alnaif 23

CHAPTER TWO Classical Epidemiology Agents v Nutrients v Poisons v Allergens v Radiation v Physical trauma v Microbes v Psychological experiences 23/03/42 Dr. Mohammed Alnaif 24

CHAPTER TWO Classical Epidemiology Person Agents 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. 23/03/42 Dr. Mohammed Alnaif 25

CHAPTER TWO Classical Epidemiology Person v Age v Socio-economic status v Gender v Ethnicity/Race v Behavior 23/03/42 Dr. Mohammed Alnaif 26

CHAPTER TWO Classical Epidemiology person or host factors v Genetic endowment v Immunologic state v Age v Personal behavior 23/03/42 Dr. Mohammed Alnaif 27

CHAPTER TWO Classical Epidemiology Person It is obvious that people differ in terms of their susceptibility or response to the agents; this is what we call person or host factors. 23/03/42 Dr. Mohammed Alnaif 28

CHAPTER TWO Classical Epidemiology Person Year 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. 23/03/42 Dr. Mohammed Alnaif 29

CHAPTER TWO Classical Epidemiology Person Other 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. 23/03/42 Dr. Mohammed Alnaif 30

CHAPTER TWO Classical Epidemiology Person A 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. 23/03/42 Dr. Mohammed Alnaif 31

CHAPTER TWO Classical Epidemiology Person Finally, 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. 23/03/42 Dr. Mohammed Alnaif 32

CHAPTER TWO Classical Epidemiology Place Geographically restricted or widespread (pandemic)? Relation to water or food supply. Multiple clusters or one? 23/03/42 Dr. Mohammed Alnaif 33

CHAPTER TWO Classical Epidemiology Place It 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. 23/03/42 Dr. Mohammed Alnaif 34

CHAPTER TWO Classical Epidemiology Environment v Crowding v Atmosphere v Modes of communication – phenomena in the environment that bring host and agent together, such as: v Vector v Vehicle v Reservoir 23/03/42 Dr. Mohammed Alnaif 35

CHAPTER TWO Classical Epidemiology Place These 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. 23/03/42 Dr. Mohammed Alnaif 36

CHAPTER TWO Classical Epidemiology Place The 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. 23/03/42 Dr. Mohammed Alnaif 37

CHAPTER TWO Classical Epidemiology Time v Changing or stable? v Seasonal variation. v Clustered (epidemic) or evenly distributed (endemic)? v Point source or propagated. 23/03/42 Dr. Mohammed Alnaif 38

CHAPTER TWO Classical Epidemiology Time Variations 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. 23/03/42 Dr. Mohammed Alnaif 39

CHAPTER TWO Classical Epidemiology Time The influence of time can also be seen in disorders that occur cyclically or seasonally, example infectious diseases such as the flu. 23/03/42 Dr. Mohammed Alnaif 40

CHAPTER TWO Classical Epidemiology SOME OTHER TERMS YOU SHOULD KNOW An 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: 1. Carrier, people who are susceptible to the disease, although they may not be affected by it themselves. 2. Vector, intermediate organisms that carry the disease but do not have it, such as the anopheles mosquito for malaria or fleas for the plague. 23/03/42 Dr. Mohammed Alnaif 41

CHAPTER TWO Classical Epidemiology SOME OTHER TERMS YOU SHOULD KNOW An 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. 23/03/42 Dr. Mohammed Alnaif 42

CHAPTER TWO Classical Epidemiology SOME OTHER TERMS YOU SHOULD KNOW An 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. 23/03/42 Dr. Mohammed Alnaif 43

CHAPTER TWO Classical Epidemiology SOME OTHER TERMS YOU SHOULD KNOW When 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. 23/03/42 Dr. Mohammed Alnaif 44

Thank You 23/03/42 Dr. Mohammed Alnaif 45