Insights into Epidemiology and Demography: Modern Applications and Theories

1. EpidemiologicandResearchApplications. Epidemiology, Demography - ApplicationsinCommunityHealthNursing By SYDORENKO OKSANA, MD, PhD

2. Lecture objectives After the lecture, you should be able to: • Describe theories of causality in health and illness. • List the major sources of epidemiologic information. • Distinguish between incidence and prevalence in health andillness states. • Use epidemiologic methods to describe an aggregate’s health. • Discuss the types of epidemiologic studies that are useful forresearching aggregate health. • Use the seven-step research process when conducting anepidemiologic study.

3. Epidemiology is the study of the determinants anddistribution of health, disease, and injuries in humanpopulations. • It is a specialized form of scientific researchthat can provide health care workers, including communityhealth nurses, with a body of knowledge on which tobase their practice and methods for studying new and existingproblems.

4. Eras of Modern Epidemiology • Four distinct eras, each based on causal thinking: • sanitary statistics(1800–1850), • infectious-disease epidemiology(1850–1950), • chronic-disease epidemiology(1950–2000), • eco-epidemiology – emerging now.

5. Major Uses of Epidemiology 1. Historical study: Is community health getting better or worse? 2. Community diagnosis: What actual or potential health problems are there? 3. Working of health services • * Efficacy • * Effectiveness • * Efficiency 4. Individual risks and chances • * Actuarial risks • * Health hazards/risk appraisal

6. Major Uses of Epidemiology 5. Completing the clinical picture: Different presentation of the disease. 6. Identification of syndromes: “lumping and splitting” 7. Search for causes: case control and cohort studies. Other uses include: Evaluation of presenting signs and symptoms, and clinical decision analysis.

7. Basic Methods in Epidemiology: Sources of Data • Data collected for other purposes • census, birth & death cert, surveillance data by CDC • Routinely collected data • medical and insurance records • Data collected for specific epi studies • original data

8. Vital Statistics • Information about births and death • * collected since mid 17th century • Fertility and natality include characteristics such as sex, weight, place of residence, gestational length, characteristics of parents. • * collected since mid 17th century • Classification according to International Classification of Diseased (ICD)

9. Demography • Demography (literally, writing about the people, from the Greek demos [people] and graphos [writing]) is the statistical study of human populations with reference to size and density, distribution, and vital statistics. • Demographic statistics provide information about significant characteristics of a population that influence community needs and the delivery of health care services.

10. Demography • Demographic studies (that is, demographic research) provide descriptions and comparisons of populations according to the characteristics of age; race; sex; socioeconomic status; geographic distribution; and birth, death, marriage, and divorce patterns. • Demographic studies often have health implications that may or may not be addressed by the investigators. The census of the U. S. population is an example of a comprehensive descriptive demographic study conducted every 10 years.

11. Demographics • total # of people, i.e. in the cuontry, state, localities. • These are done q 10 yr. via census. • May be presented as raw data or as in Frequency of Events.

12. Essential Concepts of Epidemiology • Causality • Risk • Rates of Occurrence

13. Theories of causality in health and illness. • Causalityrefers to the relationship between a cause and its effect. • A purpose of epidemiologic study has been to discovercausal relationships, so as to understand why conditions developand offer effective prevention and protection.

14. Criteria for Causality • 1. Consistency of findings • 2. Strength of association • 3. Specificity of association • 4. Temporal sequence • 5. Dose/response relationship • 6. Coherence/biological plausibility *

15. Single cause/single effect theory • Chain of causation in infectious disease.

16. Concept of multiple causation • has emergedto explain the existence of health and illness states and to provideguiding principles forepidemiologic practice. • Example: Dever’s Epidemiological model

17. Dever’s Epidemiological Model • It considers the healthstatus of the host and how it is impacted by human biology,life-style, environment, and the health care system. • Sometimes referred to as a “web of causation,” thismodel attempts to identify all possible influences on thehealth and illness processes.

18. Dever’s Epidemiological Model

19. Dever’s Model • 4 Elements • human biology: • genetics, physiologic fx, maturation. • life-style: • employment, consumption, leisure • environment: • physical, psychological, social • health-care system: • availability, accessibility, utilization

20. Web of causation for myocardial infarction.

21. Recognition of multiple causes providesmany points of intervention for prevention, health promotion,and treatment. • For example, previous Figure suggests interventions such as directly attacking significant coronaryatherosclerosis (bypass surgery), reducing the incidence ofobesity, helping people stop smoking, developing an exerciseprogram, and making dietary modifications.

22. Association • It is a concept that is helpful in determiningmultiple causality. • Events are said to beassociated if they appeartogether more often than would be the case by chancealone. Such events may include risk factors or other characteristicsaffecting disease or health states. • Examples: • frequent association of cigarette smoking with lung cancer, • frequent association of obesity with heart disease.

23. Natural History Model • Any disease or health condition follows a progression knownas its natural history; this refers to events that occur beforeits development, during its course, and during its conclusion.

24. Natural History Model • Course of Disease Process I. Prepathogenesis State • Incubation Period: • time of exposure to an infectious organism, until one develops the symptoms. • Induction or Latency Period: (noninfectious diseases) • The time during which agent-host-environment interact before symptoms appear, (years to decades) i.e.. ca, ulcers, ht dis, etc.. • Mode of transmission

25. Natural History Model • II. Pathogenesis • signs & symptoms of disease appear • illness can be detected until recovery, disability, or death. • III. Resolution • death, disability, recovery

26. Levels of Prevention • Primary ........... Prepathogenesis • immunization, diet & exercise • Secondary ........... Pathogenesis • pap smear; screening for HIV • Tertiary .................. Resolution • physical therapy, surgery, medical rx

27. Levels of Prevention • I. Primary Prevention = Health Promotion and Education • Improving Host, Agent, Environment conditions • Adequate provision for basic needs • Anticipatory action = Health Protection • Improved housing and sanitation for waterborne Ds • Removal of environmental hazards – accidents

28. Levels of Prevention II. Secondary Prevention • Detection = Early Diagnosis • Screening programs • Intervention = Prompt Treatment • Initiate prompt treatment • Arrest progression • Rehabilitation • Prevent associated disability

29. Levels of Prevention III. Tertiary Prevention : • Functional adaptation & Rehabilitation • Reducing degree of disability/damage from crisis • Reducing risk of future crisis

30. Natural History of Disease • The four stages of the natural history of disease can applyto an understanding of any health condition, includingwellness states. • In stage one, susceptibility, people can becomeamenable to healthier practices and improved healthsystem organization. • In stage two, adaptation/exposure, acommunity can learn about these health-promoting behaviors. • Stage three, early onset, could be a period of trying outthe beneficial policies and activities. • Stage four, culmination,could encompass full adoption and a higher level ofwell-being for the community. This approach has importantimplications for community health nursing preventive andhealth-promotion practice.

31. Types Of Epidemiologic Studies • Descriptive epidemiology • describes disease according to person, place, time .. • Analytic epidemiology • understand etiology of disease..........case-control, cross-sectional study, cohort studies (development of disease) • Experimental studies • clinical trials, screening

32. Descriptive epidemiology • The simplest measure of description is a count. • For example,an epidemiologic study of varicella deaths among all agegroups tracked varicella deaths through hospital dischargerecords and death certificates in New York State

33. Descriptive epidemiology • Ratesare statistical measures expressing the proportion ofpeople with a given health problem among a population atrisk. • Rates:Way of expressing the frequency of an event as a fraction or part of a whole population. • The total number of people in the group serves as the denominatorfor various types of rates.

34. Risk Risk: probability that given individual will develop a specific condition 1. Populations are at risk • because they do or do not have contributing factors. 2. Risk factors • predisposing factors that make a person/population more susceptible to a disease or event.

35. Rates In Epidemiology • the prevalence rate, • the period prevalence rate, • the incidencerate.

36. The prevalence rate • Prevalencerefers to all of the people with a particularhealth condition existing in a given population at a given pointin time.

37. The prevalence rate • If a nurse discovers 50 casesof measles in an elementary school, that is a simple count. • Ifthat number is divided by the number of students in theschool, the result is the prevalence of measles. • For instance,if the school has 500 students, the prevalence of measles onthat day would be 10% (50 measles/500 population).

38. The period prevalence rate • The prevalence rate over a definedperiod of time is called a period prevalence rate:

39. The incidencerate • Not everyone in a population is at risk for developing adisease, incurring an injury, or having some other health-relatedcharacteristic. The incidence rate recognizes this fact. • Incidencerefers to all new cases of a disease or health conditionappearing during a given time. • Incidence rate describesa proportion in which the numerator is all new casesappearing during a given period of time and the denominatoris the population at risk during the same period.

40. The incidencerate Example, • some childhood diseases give lifelong immunity. Thechildren in a school who have had such diseases would be removedfrom the total number of children at risk in the schoolpopulation. Three weeks after the start of a measles epidemicin a school, the incidence rate describes the number of casesof measles appearing during that period in terms of the numberof persons at risk:

41. The incidencerate • The health literature is not always consistent in the useof the term incidence; sometimes, this word is used synonymouslywith prevalence rates.

42. The incidencerate Example • Incidence of TB in Salem, MA in 1995: 20 new cases ______________________________ 40,000 total population @ midyear 20 ̶̶–––––– x 1,000 = (Standard measure) 40,000

43. The incidencerate • Another rate that describes incidence is the attack rate. • An attack ratedescribes the proportion of a group or populationthat develops a disease among all those exposed to aparticular risk. • This term is used frequently in investigationsof outbreaks of infectious diseases such as influenza.

44. Computing Rates • To make comparisons between populations, epidemiologistsoften use a common base population in computing rates. • Forexample, instead of merely saying that the rate of an illness is13% in one city and 25% in another, the comparison is madeper 100,000 people in the population. • This population base canvary for different purposes from 100 to 100,000.

45. Computing Rates • To describethe morbidity rate, which is the relative incidence of diseasein a population, the ratio of the number of sick individuals tothe total population is determined.

46. The mortality raterefersto the relative death rate, or the sum of deaths in a given populationat a given time.

47. Variations in Mortality and Morbidity • AGE: • *Death rates/with age, after age 40. Doubling with each decade. • *Age Pyramids reflect patterns of birth and death. • *Rate of chronic illness increases with age (despite age related prevalence,there are wide disparities cross nationally and socio-culturally) • *Rates of violence/injury related death decrease with age. • *Compression of morbidity is a topic of debate and concern with broad socio-political implication.

48. Variations in Mortality and Morbidity • GENDER: • *During the 1800’s women died younger than men, but since the 1920’s women have been living longer than men. In 1980: Women: averaged 78.6 years, while Men: averaged 71.8 years • (This pattern is not followed in all countries due to maternal mortality.) • *Men die earlier with more life threatening illness, however women display more frequent illness. • *Women have more chronic illness, but they tend to be less severe. • *Women report more episodes of illness and more doctor visits. • *Men are more likely to engage in high-risk behavior such as fast driving, smoking etc.. (These patterns are changing in the US). Research on personality types suggests gender differences that may effect illness patterns. • *Biological factors such as hormones may account for some differences but are not sufficient to explain patterns.

49. ThreeCategories of Rates • Crude, Specific, and Adjusted • Rates computed for a population as a whole are crude rates. • E.g., crude mortality rate • Subgroups of a population may have differences not revealed by the crude rates. Rates calculated for subgroups are specific rates. • E.g., age-specific death rate • In comparing populations with different distributions of a factor known to affect the health condition of interest, the use of adjusted rates may be appropriate. • Adjusted rates are helpful in making community comparisons, but they are imaginary: caution is necessary when interpreting.

50. CONDUCTING EPIDEMIOLOGICRESEARCH 1. Identify the problem. 2. Review the literature. 3. Design the study. 4. Collect the data. 5. Analyze the findings. 6. Develop conclusions and applications. 7. Disseminate the findings.