1. Foundations of Epidemiology
Chapter 1
Foundations of Epidemiology

2. What Is Health?
The absence of illness
Six dimensions of health

3. What Are the Six Dimensions of Health?
Physical
Ability of the human body to function properly; includes physical fitness and activities of daily living.
Social
Ability to have satisfying relationships; interaction with social institutions and societal mores.
Mental
Ability to think clearly, reason objectively, and act properly.
Emotional
Ability to cope, adjust and adapt; self-efficacy and self-esteem.
Spiritual
Feeling as if part of a greater spectrum of existence; personal beliefs and choices.
Environmental
Comprised of external factors (i.e., one’s surroundings such as habitat or occupation) and internal factors (i.e., one’s internal structure such as genetics).

4. What Is Public Health?
Public health is the science and art of promoting health and extending life on the population level.
Public health is concerned with threats to health in the population (a group of people sharing one or more characteristics).
The mission of public health is to ensure conditions that promote the six dimensions of health in the population as a whole.

5. What Is the Meaning of Population?
Population refers to a collection of individuals that share one or more observable personal or observational characteristic from which data may be collected and evaluated.
Social
Economic
Family (marriage and divorce)
Work and labor force
Geographic factors

6. How Does Public Health Relate to Epidemiology?
There are many subfields of public health, including epidemiology, biostatistics, and health services.
Because of its central role in public health, epidemiology is commonly referred to as the foundation of public health.

7. What Is Epidemiology?
Epidemiology is the study of the distribution and determinants of health-related states or events in human populations, and the application of this study to prevent and control health problems.

8. What Is Epidemiology?
The word epidemiology is based on the Greek words:
epi – prefix meaning on, upon, or befall
demos – root meaning the people
logos – suffix meaning the study
In other words, epidemiology is the study of what befalls the population.

9. Key Terms in the Definition
Study – Epidemiology involves sound methods of scientific investigation
Methods rely on careful observation and the use of valid comparison groups to determine whether the observed health events differ from what might be expected.

10. Key Terms in the Definition
Distribution
Study of frequency and pattern of health events in the population
Frequency – number, and number in relation to the population
Pattern – the health-related state or event by person, place, and time characteristics

11. Key Terms in the Definition
Determinants
Search for causes and other factors of health-related states or events

12. Key Terms in the Definition
Health-related states or events
Disease states
cholera, influenza, pneumonia, mental illness
Conditions associated with health
physical activity, nutrition, environmental poisoning, seat belt use, and provision and use of health services
Events
injury, drug abuse, and suicide

13. Key Terms in the Definition
Application of this study to prevent and control health problems

14. Why is epidemiology considered by many to be the foundation of public health?
Because of its central role in carrying out the three core public health functions:
The assessment and monitoring of the health of communities and populations at risk to identify health problems and priorities.
The formulation of public policies designed to solve identified local and national health problems and priorities.
To assure that all populations have access to appropriate and cost-effective care, including health promotion and disease prevention services, and evaluation of the effectiveness of that care.

15. The Epidemiologic Focus
Clinical focus vs. epidemiologic focus
Clinical focus treats the patient as an individual
Epidemiologic focus provides information that helps determine public health action to prevent and control health problems

16. Epidemiology and the Scientific Method
Epidemiology uses the scientific method to describe and analyze health-related states or events.

17. What Is the Scientific Method?
The scientific method involves using appropriate study designs and statistical techniques for investigating an observable occurrence and acquiring new knowledge.
The health problem
Hypotheses
Statistical testing
Interpretation
Dissemination

18. Study Designs in Epidemiology
Descriptive epidemiology
Involves study designs used to answer Who?, What?, When?, and Where?
Analytic epidemiology
Involves study designs used to answer Why? and How?
Later chapters will focus on describing these study designs.

19. The Importance of Descriptive Epidemiology
A means to characterizing the distribution of health-related states or events by
Person – who?
Place – where?
Time – when?
Clinical criteria – what?

20. The Importance of Analytic Epidemiology
A means to identifying and quantifying associations, testing hypotheses, and supporting statements about causality
Explains why and how health-related states or events occur

21. Selected Activities Performed in Epidemiology
Identifying risk factors for disease, injury, and death
Describing the natural history of disease
Identifying individuals and populations at greatest risk for disease
Identifying where the public health problem is greatest
Monitoring diseases and other health-related events over time
Evaluating the efficacy and effectiveness of prevention and treatment programs
Obesity increases a person's risk of illness and death due to diabetes, stroke, coronary artery disease, hypertension, high cholesterol, and kidney and gallbladder disorders. Obesity may increase the risk for some types of cancer. It is also a risk factor for the development of osteoarthritis and sleep apnea.

22. Selected Activities Performed in Epidemiology
Providing information useful in health planning and decision making for establishing health programs with appropriate priorities
Assisting in carrying out public health programs
Being a resource person
Communicating public health information

23. Epidemiology in public health practice and individual decision making
Epidemiological findings contribute to
Preventing and controlling disease, injury, disability, and death
How?
By providing information that leads to informed public health policy and planning, as well as individual health decision making

24. Selected Types of Epidemiologic Information
Public health assessment
Causes of disease
Completing the clinical picture
Program evaluation
Efficacy
Effectiveness

25. Questions That Need Epidemiology
Diagnosis
Is there such a problem as myalgic encephalitis?
Is prostate specific antigen a good test for prostate cancer?
Causes
Why did this patient suffer a stroke?
Is obesity the cause of metabolic syndrome?

26. Questions That Need Epidemiology
Treatment
Is this the best treatment for Parkinson’s disease?
Is my surgery as good as that of everyone else?
Prognosis
What are the chances of a recurrent heart attack?
How long will this knee joint prosthesis last?

27. Questions That Need Epidemiology
Health promotion and protection
Do current school meals harm children’s future health?
Will the Irish smoking ban in public places work better than the English policy?
Health and disease surveillance
Why are there tenfold international differences in suicide rates?
When will the next influenza pandemic occur?

28. Questions That Need Epidemiology
Health inequalities
Why should life expectancy be nearly five years lower in unskilled manual workers?
Do health services reduce or increase health inequalities?

29. Epidemic, Endemic, and Pandemic
Epidemic – Health-related state or event in a defined population above the expected, over a given period of time
Endemic – Persistent, usual, expected health-related state or event in a defined population over a given period of time
Pandemic – Epidemic affecting a large number of people, many countries, continents, or regions

30. Common Source, Propagated, and Mixed Epidemics
Point
Intermittent
Continuous
Propagated
Spread from person to person
Mixed epidemics
A mixture of common source and mixed
Looks like you stopped half way. 25 is random
Propagated- person to person

31. Common Source
Tend to result in more cases occurring more rapidly and sooner than host-to-host epidemics
Identifying and removing exposure to the common source typically causes the epidemic to rapidly decrease

32. Common Source Examples
Anthrax, traced to milk or meat from infected animals
Botulism, traced to soil-contaminated food
Cholera traced to fecal contamination of food and water

33. Propagated
Arise from infections being transmitted from one infected person to another
Transmission can be through direct or indirect routes
Host-to-host epidemics rise and fall more slowly than common source epidemics

34. Propagated
Examples
Tuberculosis
Whooping cough
Influenza
Measles

35. Mixed Epidemics
Occurs when a common source epidemic is followed by person-to-person contact and the disease is spread as a propagated outbreak
Example – Shigellosis occurred among a group of 3,000 women attending a music festival. Over the next few weeks, subsequent generations of shigella cases spread by person-to-person transmission from festival attendees.

36. Disease Transmission Disease transmission usually occurs by
direct, person-to-person contact (e.g., STDs)
fomite-borne (e.g., Hepatitis A spread by a contaminated eating utensil)
vehicle-borne (e.g., HIV/AIDS spread through needle sharing drug users)
vector-borne (e.g., Malaria spread through mosquitoes)
A fomite is an inanimate object. A vector is an invertebrate animal. Vehicle-borne transmission is related to fomites.

37. Accurate Assessment Requires a Standard Case Definition
A standard set of criteria, or case definition, assures that cases are consistently diagnosed, regardless of where or when they were identified and who diagnosed the case

38. Concepts and Principles of Case as Used in Epidemiology
A case is a person who has been diagnosed as having a disease, disorder, injury, or condition

39. Primary Case, Index Case
The first disease case in the population is the primary case
The first disease case brought to the attention of the epidemiologist is the index case
The index case is not always the primary case

40. Secondary Case
Those persons who become infected and ill after a disease has been introduced into a population and who become infected from contact with the primary case

41. Different Levels of Diagnosis
Suspect
An individual who has all of the signs and symptoms of a disease or condition, yet not diagnosed
Confirmed
All criteria met

42. Different Levels of Diagnosis
As more information (e.g., laboratory results) becomes available to the physician, he or she generally upgrades the diagnosis. When all criteria are met and they meet the case definition, the case is classified as a confirmed case.

43. Epidemiology Triangle for Infectious Disease
The interrelatedness of four epidemiological factors often contributed to an outbreak of a disease: (1) the role of the host, (2) an agent or disease-causing organism, (3) the environmental circumstances needed for a disease to thrive, survive, and spread, and (4) time-related issues.

44. Triangle is based on the communicable disease model
Shows the interaction and interdependence of agent, host, environment, and time as used in the investigation of diseases and epidemics.
Agent – cause of the disease
Host – an organism, usually a human or an animal, that harbors a disease
Environment – includes those surroundings and conditions external to the human or animal that cause or allow disease transmission
Time – accounts for incubation periods, life expectancy of the host or the pathogen, and duration of the course of the illness or condition

45. Stopping an Epidemic
An epidemic can be stopped when one of the elements of the triangle is interfered with, altered, changed, or removed from existence, so that the disease no longer continues along its mode of transmission and routes of infection.

46. Some Disease Transmission Concepts
Fomites
Objects such as clothing, towels, and utensils that may harbor a disease agent and are capable of transmitting it; usually used in the plural
Example – transmission of cutaneous anthrax from drums to an individual

47. Vector
An invertebrate animal (e.g., tick, mite, mosquito, bloodsucking fly) capable of transmitting an infectious agent among vertebrates
Transmission can be mechanical (agent does not undergo physiologic changes within the vector) or biological (agent undergoes a part of its life cycle within the vector before transmission to new host)
Can spread an infectious agent from an infected animal or human to other susceptible animals or humans through its waste products, bite, or body fluids, or indirectly through food contamination

48. Reservoir
The habitat (living or nonliving) on which an infectious agent lives, grows, multiplies, and depends on for its survival in nature
Humans, animals, food, feces, decaying organic matter
Humans often serve as both reservoir and host
Public health officials often attack the reservoir of an agent at the environment leg of the triangle of epidemiology. The chain of infection can be broken by destroying the vector in the environment in which it lives. Airplanes are often used to spray the watery breeding places (environment) of mosquitoes in order to kill this vector of malaria, St. Louis encephalitis, yellow fever, and west nile virus.

49. Zoonosis When an animal transmits a disease to a human
Examples – rabies, Rocky Mountain spotted fever, shigellosis

50. Carrier A carrier contains, spreads, or harbors an infectious organism
Example – Typhoid Mary
Five types of carriers

51. Carrier
Active – Individual has been exposed and has been harboring disease-causing pathogen; may or may not be recovered
Convalescent – Individual in recovery from disease who is still infectious
Healthy – Individual has been exposed and harbors disease-causing pathogen but shows no symptoms

52. Carrier
Incubatory – Individual has been exposed and is harboring disease-causing pathogen in beginning stages of the disease, has symptoms, and is infectious
Intermittent – Individual in recovery from disease who is still infectious in different places or time intervals

53. Modes of Disease Transmission
Direct transmission – Direct physical contact such as touching with contaminated hands, skin-to-skin contact, kissing, or sexual intercourse
Indirect transmission – Occurs when pathogens or agents are transferred or carried by some intermediate item, organism, means, or process to a susceptible host, resulting in disease

54. Advanced epidemiology triangle for chronic diseases and behavioral disorders
Goes beyond infectious disease to include behavior, lifestyle factors, environmental causes, ecological elements, physical factors, and chronic diseases must be taken into account.

55. Chain of Infection
Disease transmission occurs when pathogen leaves the reservoir (e.g., food, water, feces, animal) through a portal of exit (mucous, membranes, wounds) and is spread by a mode of transmission (direct or indirect). Pathogen then enters the body through a portal of entry (mucous membranes, wounds) and infects susceptible host.

56. Chain of Infection

57. Other Models of Causation
Rothman’s Causal Pies

58. Active Primary Prevention
Requires behavior change on part of subject
Wearing protective devices
Health promotion
Lifestyle changes
Community health education
Ensuring healthy conditions at home, school, and workplace

59. Passive Primary Prevention
Does not require behavior change
Vitamin-fortified foods
Fluoridation of public water supplies

60. Secondary Prevention Occurs to reduce the progress of disease
The disease already exists in the person
Cancer screening – Cancer already present; the goal is to detect the cancer before clinical symptoms arise in order to improve prognosis and prevent conditions from progressing and from spreading

61. Tertiary Prevention
To reduce the limitation of disability from disease
The disease has already occurred
Physical therapy for stroke victims
Halfway houses for recovering alcoholics
Shelter homes for the developmentally disabled
Fitness programs for heart attack patients