Introduction to Public Health and Epidemiology

1. Introduction to Public Health and Epidemiology HCA 202 Chris Cochran, Ph.D. August 29, 2005

2. Brief History of Public Health: Greco-Roman Period • Hippocrates: “Whoever wishes to pursue properly the science of medicine … ought to consider the effects of the season of the year, the hot winds and the cold, the properties of the waters, the setting of the town, the behavior of the people • Romans build aqueducts to bring water from distant sources and to remove sewage

3. Brief History of Public Health: The Middle Ages • Public health declines • Disease and lack of sanitation rampant • Increase in trade between cities also enabled the spread of disease • Bubonic plague hits Europe between 1349-1354 killing one-third of the population • By the end of the middle ages, healthcare starts to redevelop; rudimentary food-safety guidelines are introduced

4. Brief History of Public Health: The Renaissance Lost knowledge reemerges • First systematic classification of diseases undertaken. • Occupational related disease is first identified by Paracelsus. This knowledge is still used today.

5. History of Public Health: The Enlightenment • First surveys seeking information related to diseases and health are developed • Edward Jenner observed that milkmaids who had cowpox did not contract smallpox • Industrial revolution improves sanitation but creates new environmental hazards of water and air

6. Brief History of Public Health:The Sanitary Movement • Regular bathing, clean water and controlled waste disposal is promoted • To control fires, New York constructs one of the first municipal water systems • River and Harbor Act of 1899, implemented by federal government to protect waterways from dumping of debris becomes the basis for protection from pollutants • Pasteur and Koch develop germ theory of disease • John Snow initiates the study of Epidemiology • Science and engineering expands at rapid pace furthering the advance of medicine • Use of antiseptics in hospitals allows them to become places where the sick can be treated, not places to die

7. Brief History of Public Health:The Age of Bacteria • Connection made between bacteria and viruses and disease • Pasteurization U.S. adopts the Pure Food and Drug Act • Important species of bacteria are isolated and identified including Escherichia coli and staphylococcus • Identification of vectors helps battle communicable disease. • Elements of the immune system are identified creating regional laboratories devoted to disease research • Drinking water and sewage treatment plants causes a decline in typhoid

8. Brief History of Public Health:Modern Times • WWI introduced poison gas as warfare • Draining of swamps reduces mosquito borne disease • In 1919, “Spanish Flu” pandemic killed 30 million world-wide • Fleming discovers penicillin in 1928 • In WWII, protecting soldiers from disease leads to more death from injuries and wounds than from infection for the first time in history of wars • The World Health Organization was formed in 1948 • Salk invents the polio vaccine • In 1978, smallpox is eradicated from the planet • In 1979, the first cases of AIDS appear • In 1980s, poison gas once again used in warfare (Iran-Iraq war) • New diseases emerge: AIDS, SARS, drug-resistant staphylococcus

9. Public Health: Priorities for the Future • Continue the pursuit of the eradication of disease and its causes • Getting the public to understand that preventing disease does not rely solely on new medicine or inventions • Making sure that we don’t undo the advances that we have already made

10. What is Health • A state of complete physical, mental and social well-being, not merely the absence of disease or infirmity (WHO). • Preventing premature death and preventing disability, preserving a physical environment that supports human life, cultivating family and community support, enhancing each individual’s inherent abilities to respond to and to act, and assuring that all Americans achieve and maintain a maximum level of functioning. (Healthy People 2010)

11. Epidemiology Defined for Course • THE STUDY OF THE DISTRIBUTION AND DETERMINANTS OF DISEASES AND INJURIES IN HUMAN POPULATIONS • Concerned with frequencies and types of illnesses and injuries in groups of people & factors that influence their distribution • Implies that disease is not randomly distributed • Speculates that a chain of events must occur for illness or disability to take place

12. Epidemiology • Endemic – habitual presence of a disease for a population within a given geographic area expectations • Epidemic – occurrence of a group of illnesses within a given geographic area in excess of normal expectations • Pandemic – world-wide or broad epidemic beyond many geographic regions

13. Objectives of Epidemiology • Identify the etiology or cause of disease and risk factors • Determine the extent of the disease in the community • To study the natural history and prognosis of the disease • To evaluate existing and new preventive measures and therapeutic measures and modes for health care delivery • To help make public policy

14. The Relationship of Epidemiology to Health Care Managers • Understanding the increase/decrease in size of service populations • To understand the characteristics and health status of the population for planning purposes • To understand the consequences of health care problems • To mesh the service organizations to the needs of the population • To monitor performance by the organizations • To modify the structure and processes and respond to environmental change • To better formulate and evaluate public policy

15. Life Expectancy at Birth

16. Life Expectancy at Birth and at age 65 years 1900, 1950, and 2000

17. THE EPIDEMIOLOGICAL TRIAD HOST VECTOR AGENT ENVIRONMENT

18. Classification for Health Status Today • Disease – a state of dysfunction of the normal physiological processes manifested as signs, symptoms, and abnormal physical or social function (includes injury). • Functional Ability – a process used to represent how independently an individual can perform or fulfill expected social roles (physical and mental). • Quality of Life – multidimensional concepts of measures covering symptoms/problem complexes, mobility, physical activity, emotional well-being and social functioning.

19. Blum’s Model of Factors Affecting Health Health • Environment • Fetal • Physical • Socio/Cultural • Lifestyle • Attitudes • Behavior Biology • Medical Care • Prevention • Cure • Care • Rehabilitative

20. Prevention and Health Promotion • Primary – inhibition of the development of the disease before it occurs • Secondary – early detection and treatment of a disease • Tertiary – the rehabilitation or restoration of effective functioning

21. Primary Cause of Death 1900

22. Primary Cause of Death 1997Source: Healthy People 2010

23. Descriptive Epidemiology: Person, Place and Time • Person Measures • Age • Sex • Ethnic group and race • Social class/social-economic status

25. Place Measures • Place – related by natural barriers or by political boundaries. • Natural boundaries – characterized by particular environmental or climatic condition (temperature, humidity, rainfall, altitude, mineral content, etc.). • Place diseases – parasitic diseases that may be due to certain factors such as tropics, temperate, or other conditions. • Political subdivisions – vary from entire nations to counties, cities, towns, and boroughs

26. Time and Place • Time – basic aspect of epidemiology • Secular trends (long-term variations, which occur over periods of time including years and decades). Good for studying "birth cohorts". • Cyclic change – recurrent alteration in the frequency of disease (seasonal changes, for example – influenza) • Clusters in time and place – difficult to determine the significance of linkages because there is no defined denominator

27. Using Rates In Epidemiology • Numerator - the number of people/cases with the disease • Denominator - (the population at risk)

28. Basic Descriptive Rates • Rate - Number of events, cases, or deaths in a time period/Population in same area • Ratio – Expresses the relationship between 2 numbers in the form of x:y or (x/y)k. • Proportion – Specific type of ratio with the resultant value expressed as a percent.

29. DEATH RATES • Three essential components of death rates: • A population group exposed to the risk of death • A time period • The number of deaths occurring in the population during that time period (NOTE: best to take the population for the mid-point of the period being studied.

30. Types of Rates • Crude Death Rate: Total # deaths from all causes during a 12 month period  Total # persons in the population at the midpoint of the period • Cause specific death rates: # deaths from a specific disease  # persons in the population at the midpoint of the period • Age specific death rates: # deaths in a specific age group  # persons in that age group; Usually X 100,000 • Case fatality rate: Represents the risk of dying over a specified period of time for people with a certain disease • Proportionate mortality ratio: Represents the proportion of total deaths that are due to a specific cause. • Does not represent the risk of dying. • # deaths from a specific disease  Total # deaths in the population X 100 to express as a percent

31. Other Rates To Consider • Gender Specific • Race Specific • Infant Mortality Rates • Infant Mortality Rate – Birth to 1 year; Denominator is live births • No. of deaths < 1 year of age/No. of live births • Neonatal Mortality Rate • Post-neonatal Mortality Rate • Perinatal Mortality Rate

32. Years of Productive Life Lost before Age 65 among Children less than 20 Years

33. Incidence And PrevalenceKnowing Which Is Which • Incidence measures the number of new cases in an at-risk population • Prevalence measures the number of existing cases in an at-risk population • Point Prevalence - the number of existing cases of a disease at a specific period of time. This includes new cases (Incidence). • Period Prevalence - refers to the number of cases during a period or interval. This can include new and recurring cases.

34. Uses of Incidence and Prevalence • Prevalence is useful as planning tool • Can be used to express burden of some attribute in the population • Can monitor control programs for chronic illness • Point prevalence can track illness over time • Incidence rates are fundamental tools for etiologic studies of acute and chronic illness

35. Uses of Incidence and Prevalence • Comparing incidence between groups is useful for measuring affects of risk between populations • High prevalence does not signify risk, it may merely reflect a change in survival rate • Low prevalence may reflect a rapidly fatal disease (or easily curable) • Prevalence favors inclusion of chronic illness over acute illness

36. Determining the Case Fatality Rate

37. Determining the Case Fatality Rate • To determine which country has the largest annual number of new cases - obtain the rate of cases per 10,000 and compare it to the total population. • For example, country A has 4 cases per 10,000 and a total population of 250,000. For every 10,000 population there are 4 cases. Therefore, the number of new cases would be 4/10,000:n/250,000.

38. Adjusted Rates Adjusted rates or standardized rates help remove the effects of differences in composition of various populations (for example, age differences). Direct Adjusted Rates - age specific rates observed in 2 or more study populations are applied to an arbitrarily chosen standard population. Indirect rate adjustment - compares 2 or more populations in which the age-specific rates are not known or are excessively variable because of the small size of the population. In this case, the rates of the more stable population are applied to the population of the smaller group.

39. Formula for Adjusted Rates • Direct Adjusted Rates = • Σ(riNi)/Nt • Indirect Adjusted Rates = • dt/Σ(Rini)](Rt)

40. Controlling Infectious Disease

41. Controlling Infectious Diseases • Epidemic – the occurrence of cases of a condition in excess of what would be expected. • Epidemics in US during 19th Century • Smallpox • Cholera • Yellow Fever • Typhoid Fever

42. How Infectious Diseases Develop • Characteristics of the Agent • Reservoir of the Agent (where the agent lives and grows/host) • Mode of Transmission • Portal of Entry/Exit • Susceptibility of the Host

43. Class Staphylococci Streptococci Neisseriae Legionellae Mycobacteria Spriochetes Rickettsia Chlamydiae Disease Toxic Shock Syndrome Streptococcal sore throat Gonorrhea Pneumonia Tuberculosis Syphilis Typhus Urethritis Classes of Bacteria and Commonly Associated Human Diseases

44. Characteristics of Infectious Agents • Characterized in terms of biological classification • Microbiological agents include: • Bacteria • Fungi • Parasites • Viruses

45. Detection of these agents • Morphological identification in sections of tissue or stains of specimens • Culture isolation • Use of Fluorscein-labeled anti-body stains or immunologic assay • DNA/RNA or DNA-DNA hybridization • Antibody or cell-meditated immune responses

46. Components of accurately identifying infectious diseases • The specimen • Adequacy of material being tested • Selection of appropriate body area for testing • Method of Collection • Transport of the Specimen to the Lab

47. Detection Issues • Pathogeneity – the ability of an organism to alter normal cellular and physiological processes • Virulence – the ability of the organism to produce over infection • Incubation Period – the time from point of infection to onset of disease

48. Detection Issues • Reservoirs – can be living (human, animal, plant) or inanimate (soil, water) • Clinical cases • Those who manifest signs and symptoms of the disease (acute cases) • Those who are infected but don’t show signs or symptoms (subclinical or inapparent cases) • Carriers - those who serve as the source of the disease

49. Mode of Transmission • Direct transmission - actual contact with an infected host • Indirect transmission - contact with a contaminated object (contaminated needles, receptacles, etc.) • Droplet spread - such as sneezing or coughing (inhalation)

50. Hosting the Agent • Portal of Exit - where the organism leaves the body • Portal of Entry - where the organism enters the body • Host Susceptibility - depends on genetic factors, general health, and immunity. This usually refers to the condition of the host and the level of resistance. • Passive natural immunity - passed from the mother to the fetus • Passive Artificial Immunity - inoculation of specific protective antibodies • Active Immunity can be natural (previous exposure to disease or previous exposure to preventative measures) • To develop disease, individual must be susceptible and exposed