Chapter 1

1. 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

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

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. 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. 1991 Obesity Trends* Among U.S. AdultsBRFSS,1991, 1996, 2003 (*BMI 30, or about 30 lbs overweight for 5’4” person) 1996 2003 No Data <10% 10%–14% 15%–19% 20%–24% ≥25%

18. Common source, propagated, and mixed epidemics • Common source • 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

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

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

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