1. Foundations of Epidemiology
Chapter 1
Foundations of Epidemiology

2. Objectives Define epidemiology
Explain the importance of descriptive epidemiology
Explain the importance of analytic epidemiology
Explain the role of epidemiology in public health practice and individual decision making
Define epidemic, endemic, and pandemic
Describe common source, propagated, and mixed epidemics
Define the concepts and principles of case as used in epidemiology
Describe the epidemiology triangle for infectious disease
Describe the advanced epidemiology triangle for chronic diseases and behavioral disorders
Define the three levels of prevention used in public health and epidemiology
Understand basic vocabulary used in epidemiology

3. Define 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.

4. Define epidemiology The word epidemiology is based on the Greek words
epi—prefix meaning on, upon, or befall;
demos—root meaning the people; and
logos—suffix meaning the study
In other words, epidemiology is the study of what befalls the population

5. 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

6. 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

7. Key terms in the definition
Determinants
Search for causes and other factors of health-related states or events

8. Key terms in the definition
Health-related states or events
Epidemiology involves study of disease states (e.g., cholera, influenza, pneumonia)
Epidemiology also involves events
injury, drug abuse, and suicide
Epidemiology also involves behaviors and conditions associated with health
physical activity, nutrition, seat belt use, and provision and use of health services

9. The importance of descriptive epidemiology
Descriptive epidemiology involves characterization of the distribution of health-related states or events by
Person - who
Place - where
Time – when
Clinical criteria - what

10. Descriptive epidemiology
Allows us to answer who, what, and where questions
This knowledge is prerequisite to effective education, screening, prevention, and control programs
Provides policy makers with information that can be used for more effectively allocating scarce health resources. Provides individuals with information that can promote better health.

11. Analytic epidemiology
Analytic epidemiology involves identifying and quantifying associations, testing hypotheses, and identifying causes of health-related states or events
Explains why and how health-related states or events occur

12. 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
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
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.

13. Role of 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 leading to informed public health policy and planning, as well as individual health decision making

14. Public health surveillance Causes of disease
Epidemiologic information for influencing public health policy and planning and individual decisions
Public health surveillance
Causes of disease
Completing the clinical picture
Program evaluation
Efficacy
Effectiveness

15. 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

16. 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

17. Obesity Trends* Among U.S. Adults BRFSS, 1991, 1996, 2003
(*BMI 30, or about 30 lbs overweight for 5’4” person)
1996
1991
2003
No Data <10% %–14% %–19% %–24% ≥25%

18. Common source, propagated, and mixed epidemics
Point
Intermittent
Continuous
Propagated

19. 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

20. Common source Examples
anthrax, traced to milk or meat from infected animals
botulism, traced to soil-contaminated food
and cholera traced to fecal contamination of food and water

21. 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

22. Propagated
Examples
tuberculosis
whooping cough
Influenza
measles

23. 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 transmission (e.g., Malaria spread through mosquitoes)

24. 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 3000 women attending a music festival. Over the next few weeks, subsequent generations of shigella cases spread by person-to-person transmission from festival attendees.

25. 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

26. 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.

27. Secondary case
Those persons who become infected and ill once a disease has been introduced into a population and who became infected from contact with the primary case

28. Different levels of diagnosis
Suspect
Probable
Confirmed

29. Different levels of diagnosis
As more information (such as 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.

30. Suspect case
An individual or group of individuals who have all of the signs and symptoms of a disease or condition yet has not been diagnosed as having the disease, nor have the cause of the symptoms connected to a suspected pathogen (i.e., any virus, microorganism, or other substance that causes disease)

31. 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.

32. 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 is the cause of the disease
Host is an organism, usually a human or an animal, that harbors a disease
Environment is 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.

33. 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

34. 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

35. Vector
An invertebrate animal (e.g., tick, mite, mosquito, bloodsucking fly) capable of transmitting an infectious agent among vertebrates
Can spread an infectious agent from an infected animal or human to other susceptible animals or humans through its waste products, bite, body fluids, or indirectly through food contamination

36. Reservoir
The habitat (living or nonliving) on which an infectious agent lives, grows, and multiplies and is dependent on for its survival in nature
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.

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

38. Carrier A carrier contains, spreads, or harbors an infectious organism
Example – Typhoid Mary

39. Six types of carriers Active carrier Convalescent carrier
Healthy carrier
Incubatory carrier
Intermittent carrier
Passive carrier (same as healthy carrier)

40. 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

41. The chain of infection
There is a close association between the triangle of epidemiology and the chain of infection

42. 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.

43. Three levels of prevention used in public health and epidemiology
Primary prevention (occurs prior to exposure)
Immunization
Sanitation
Education
Media campaigns
Warning labels

44. Active primary prevention
Requires behavior change on part of subject
Wearing protective devises
Obtaining vaccinations

45. Passive primary prevention
Does not require behavior change
Vitamin fortified foods
Fluoridation of public water supplies

46. 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

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

48. Conclusion
Epidemiology involves application of scientific methods for describing the frequency and pattern of health-related states or events
Epidemiology identifies causes of health-related states or events and modes of transmission
Epidemiology guides public health planning and decision making
Epidemiology assists individuals in making informed health behavior changes