NRBS 300 Epidemiologic Concepts & Theory

Epidemiology Concepts and Theory: Definition, Purpose, Goal and FunctionsDefinition: Epidemiology is the study of the distribution & determinants of health & illness, morbidity, injuries, disabilities, morbidity & mortality in populations.

Epidemiology is the discipline that provides a systematicframework for examining states of health, causation ofdiseases/injuries & control of health problems in the humanpopulation.

Epidemiology is concerned with: the traditional study of diseases caused by infectious agentsHealth related problems related to suicide, climate, toxic agents environmental pollution and catastrophic radiationAsking pertinent questions related to: occurrence of diseases and state of health among populations; frequency of illnesses in geographic areas; conditions under which diseases occur; effectiveness of Rx & programs

11 Epidemiology: Definition, Purpose Goal and FunctionsEpidemiology focuses on: Factors that determine the health status of the populationControlling health problemsQuestions related to what, who, when, where, how & why in relation to distribution & description of diseases in a population Eg: Out break of measles in NYC, Global problems with AIDS, SARS etc

22 Epidemiology: Definition, Purpose Goal and Functions

Purposes of EpidemiologyTo search for causal relationships in health and illnessTo understand why conditions develop To offer effective prevention for & protection against disease and social maladies Goals of EpidemiologyDetermine the extent of disease in a populationIdentifies patterns & trends in occurrence of diseaseIdentify causes of diseaseEvaluates the effectiveness of actions for prevention & treatment of diseasesKeeps record of epidemiological data for quality improvement

33Historical Roots of EpidemiologyAncient Times: Hippocrates (460 to 375 BC): Belief that diseases affected individuals as well as the masses. Linked diseases with lifestyles & environmental factors Middle Ages:1348 - Plague (Black Death): Link between disease (The Plague) and microbes discovered and accepted by scientists. Confidence that disease can be controlled if source is eliminated. War against rats control of the plague18th century: Florence Nightingale (18201910): 1st nurse researcher to show evidence that fresh air, good nutrition, clean techniques will reduce rate of infection & death of patients. Kept epidemiologic data re health conditions of injured soldiers in the Crimean War44Historical Roots of Epidemiology19th century: Modern epidemiology based on causal thinking (see Table 7-1)Sanitary statistics (1800-1850): held that disease was caused by poisonous and malodorous particles from decomposed organic matter Infectious-disease epidemiology (1850-1950): Disease viewed in a simple cause & effect relationship. Advent of vaccines, antibiotics intended to eliminate causal agentsChronic-disease epidemiology (1950-2000): Focused on understanding & controlling chronic diseases. Linked life style with chronic diseases. Non-infectious chronic diseases # 1 cause of deaths in the USA

55Historical Roots of Epidemiology (cont)Current: Eco-epidemiology (Currently emerging):Global health patterns are in transformation.

Despite knowledge of microbes & risk factors, outbreaks of disease still occur

Knowledge of how to control AIDS- but thousands of new cases reported annually (The mystery is controlling human behavior)

With modern technology researchers are able to tract geographical distribution of diseases in relation to health risk. 66 Epidemiologic Principles and Theoretical ConceptsDisease states are best understood by a study of the: Epidemiologic triad Host, agent & environmental factorsCausalityRisk

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Copied from Allender, Rector & Warner (2005) 6th Ed88 Epidemiologic Principles and Theoretical ConceptsHost: susceptible human or animal who harbors and nourishes a disease causing agentFactors influencing susceptibility and response of host:Physical e.g.: age, sex, ethnicity and genetic risk factorsGenetic: Cystic fibrosis, Huntington's diseaseAge: Childhood illnesses, Alzheimer's diseaseSex: Rheumatoid arthritis (Female more affected)Ethnic group: sickle cell diseasePhysiological state: Fatigue, pregnancy, puberty, stress, nutritional state(Nies, Mary A.. Community/Public Health Nursing: Promoting the Health of Populations, 4th Edition. W.B. Saunders Company, 102006. 4.4). Psychological e.g.: attitude towards life, stressLifestyle: diet, exercise, sleep pattern and habitsTheoretical concept of inherent resistance:Ability of some people to resist pathogens. They are less vulnerable to diseases even after exposure to it.Related to physical, psychological and lifestyle factorsCite example99 Epidemiologic Principles and Theoretical Concepts

Factors that contribute to health problems The primary cause of a health problem or conditionFactors may be present e.g.: virus, drugs & guns or absent (e.g.: traffic light at busy intersection)5 Types of agents: -biological: fungus, insects, viruses, bacteria, worms, -chemical gas, dust, fumes -nutrient dietary excess or deficiency - physical mechanical, material, atmospheric, geographic -psychological stress related events eg job, schoolClassification of AgentsInfectious e.g.: AIDS, measlesNon infectious e.g.: stroke, diabetes, cancer

Agents:1010

1111Environment:External factors that influence vulnerability or resistance to health problems or conditionsEnvironmental factors may be physical or psycho-socialPhysical environment: climate, geography, presence of plants, insects, microbes, food and water supply

Psycho-social environment: access to health care, cultural beliefs, poverty, stressors in family, at work or school, public policies, attitudes

1212Host, agent and environment interact to cause disease or health problems.

Intervention to prevent the spread of a disease may focus on any of these 3 points.

Copied from Community Health Nursing Caring for Populations (Clark 2003, p.219)

1313Buzz Groups: 4 in each group~ Cite a health problem or condition applying the concept of the epidemiologic triad to identify host, agent and environment

~ Choose a point of intervention & discuss how the spread of the health problem or condition could be intercepted ~ In seeking to interrupt the spread of the West Nile virus, which aspect of the epidemiologic triangle is being targeted (host, agent, environment) in the following example:Avoiding mosquito bitesuse insect repellant, wear protective clothingStaying in doors at dawn and early eveningEliminating stagnant water where mosquitoes can lay eggsReporting the presence of several dead birds in the areaImplementing an organized mosquito control program

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Epidemiological Theories & ConceptsCopied from Community Health Nursing Caring for Populations (Clark 2003, p.211)1515Epidemiological Theories & Concepts:1. CausalityThe relationship between a cause and its effect

In epidemiology causal relationships between host, agent & environment are studied

One event is the result of another event.

Very linear in approach and unsuitable for understanding the multiple causes of non-infectious diseases. 1616Epidemiological Theories & Concepts (Cont)Chain of Causation (Fig 7.2): Links the transmission of an infectious disease in the following way:

Reservoir: where the causal agent livesPortal of Exit: In order for disease to be transmitted, the causative agent must leave the body of the reservoirMode of Transmission: the vehicle that transports the agent from one person to the nextCausative Agent: taken to a new portal of entry by insect, food, water, humanPortal of Entry: may be via skin, mucus membranes, vaginal, GI, respiratory, etc.Host: become infected as causative agent is deposited into the system1717

Epidemiological Theories & Concepts (Cont) Chain of Causation: Illustration 1818Concept of Multiple Causation Linear application of Chain of Causation insufficient for understanding non-infectious diseases such as CV diseases, cancer etc. 2. Concept of Multiple Causation or Web of Causation offered better understanding about the relationship between populations, health, disease & their multiple factors

1919Epidemiological Theories & Concepts (Cont)Web of Causation or Denver Epidemiological Model: Examines multiple causative agents responsible for health and illness

Considers the impact of biology, life style and environment on health status of host

Identifies all possible influences on health and illness. Forces the user to apply critical thinking skills

Useful for explaining problems that cannot be explained in single causal terms

Suggests various points where intervention may be appropriate2020

2121Basic Epidemiological Concepts (Cont)Immunity: Ability of host to resist a particular infectious disease. 4 types of immunityPassive Immunity: Short term, acquired naturally (maternal antibodies) or artificially (via inoculation with antibodies)Active Immunity: Long term naturally (from disease) or artificially acquired (via vaccine) Cross Immunity: Immunity to one disease provides immunity to other related diseases. May be passive or active. Eg natural immunity to small pox cow pox Herd Immunity: Describes level of immunity present in a given populationRisk: Probability that disease or health condition will develop in a particular group.

2222RiskProbability that a disease or unfavorable health condition will develop

Directly influenced by biology, environment, lifestyle, and system of health care.

Risk factors: negative influences

Populations at risk: collection of people among whom a health problem has the possibility of developing because certain influencing factors are present or absent or because there are modifiable risk factors

2323Epidemiological Theories & Concepts (Cont)Natural History of the Disease or ConditionRefers to a description of events that occurred:Before the development of a diseaseDuring the course of the diseaseDuring the conclusion of the diseaseInvolve interaction among host, agent and environment24242 Phases Natural History to Diseases: -Pre-Pathogenesis -Pathogenesis

Natural progression of a disease occurs in 4 stagesPhase 1: Pre Pathogenesis consists of the first 2 stages:

1st Stage: Susceptibility. Absence of disease, no exposure to condition but strong possibility for exposure. After exposure, disease will not progress if immune system is intact. E.g.: Toddlers in a day care are susceptible to measles.

2nd Stage: Subclinical Disease: -Exposure to health problem or causative agent but no symptoms of disease. -Followed by an incubation period where organism multiplies to produce a host reaction & clinical symptoms -For noninfectious disease there is an induction or latency period ie time between exposure & onset of symptoms

Epidemiological Theories & Concepts (Cont) Natural History to Diseases or Health Conditions2525Phase II Pathogenesis of Natural History:Stage 3: Clinical Disease: There is evidence of diseaseClinical signs and symptoms are presentPositive lab test for disease or conditionDisease or condition can be diagnosed at this stageEpidemiological Theories & Concepts (Cont) Natural History to Diseases or Health Conditions2626Pathogeneses Phase II Natural History contStage 4: Resolution, Recovery, Disability or Death Recognizable signs and symptoms of disease persistDisease may be mild or severeConclusion of disease may result inReturn in healthResidual or chronic form of diseaseDeathEpidemiological Theories & Concepts (Cont) Natural History to Diseases or Health Conditions2727

2828In groups of 4 5, identify a host, an agent and an environmental factor. Describe the progression of a disease or conditions in outline form.In Class Group Work2929Definitions of Health World Health Organization (WHO): A state of complete physical, mental & social well being and not merely the absence of diseases.

Other Definitions: A person physical, mental and spiritual state; may be positive or negative. A dynamic state of being

Holistic state of well being, including mind, body and spirit

Betty Neuman: Views health on a continuum- with wellness at one extreme & illness at the other. Health is equated with optimal stability, best possible wellness state. Client may experience varying levels of health.

3030Concept of Health PromotionHealth Promotion: All efforts that seek to move people closer to optimal wellness; eg health education, behavior modification. Has to do with disease prevention. May involve client as a person, family or community.

Goal: To raise public awareness of living healthy. To initiate healthful programs eg Health People 2020

Health Maintenance: Focuses on sustaining good health & providing services after returning client to a state of well-being eg medical equipment, exercise programs

3131Concern is not only with treating diseases but also involves wellness at various levels

Disease or health problems may be prevented, halted or reversed at various points during its natural history

Identifying strategic points of control and designing programs to promote wellness are primary concerns of epidemiologists

Disease control may be implemented at the primary, secondary or tertiary levels of prevention

Levels of Prevention: Strategic Points of Control 3232Primary Prevention: Aims at altering susceptibility or reducing exposure of persons who are at risk for injuries or developing a particular disease

Geared towards a generally healthy population

Involves visionary planning and implementation of programs before disease, injury or problem strikes

Seeks to prevent the occurrences of health problems

Include health promotion and disease prevention measures. E.g.: health teaching, nutritional counseling, immunizations, safety devices to prevent falls, MVA etcLevels of Prevention: Primary Prevention3333Secondary Prevention: Aims at early detection and prompt treatmentSeeks to cure or reduce progression of diseaseGeared to prevent disability and complicationsIncludes screening programs for early detection of diseases eg lead screening in toddlers, Screening susceptible people who are asymptomaticEarly case finding prompt treatment & nursing carePreventing the development of health conditionLevels of Prevention: Secondary Prevention3434Tertiary Prevention: Aims at:Reduce the extent or severity of a health problem thus limiting disability in early stages of the disease Rehabilitation for injured personsEducation to prevent further deteriorationContinued treatment and nursing careReferrals to support groups and resource agencies to offer support and help minimize loss of functionMinimizing effects of unhealthy conditions

Levels of Prevention: Tertiary Prevention3535Rates of OccurrenceExpress the proportions of people with a health condition among a population at riskExamining rates of occurrence allow comparison between groups of different sizes with respect to a particular problem e.g.: a community of 1000 reporting 50 cases of syphilis a year has the same magnitude of a problem as a city with 100,000 people reporting 5,000 cases/year

Understanding Key Terms3636Prevalence: Refers to all the people with a particular health condition, living in a given population at a specific point in time.Prevalence Study: Describes patterns of occurrence

Risk Probability that a disease will develop Directly influenced by factors such as lifestyle, environment, healthcare system, biologyNegative influences are called risk factorsKey Terms3737Incidence: refers to all new cases of a disease appearing during a given timeIncident rate describes the proportion of persons contracting the disease in relation to the population at risk during a given period of time.

Key Terms3838Population at risk: Group(s) of people who have the greatest potential to develop a particular health problem because of the presence or absence certain contributing factors.~ Clark 2003 p. 212Key Terms3939Epidemic: High incidence of a disease occurring in a community that significantly exceeds the normal or expected frequency

Pandemic: Significant increase in the incidence of a disease occurring world wide e.g.: AIDS

Mortality rate: sum of death in a given population

Morbidity: Incident of disease and disability in a given populationKey Terms40403 Major Sources of InformationExisting dataInformal investigationScientific studies1. Existing DataInformation available nationally, regionally, by state, county or urbanized area

Include vital statistics, census data, morbidity data on infectious disease

Local health departments provide data upon request and give advice on specific problemsSources of Data for Epidemiologic Study4141Describe the following sources of data and explain their relevance to the study of epidemiology. Cite examples or brief case scenarios to validate your understanding.Group A ~ vital statistics & disease registriesGroup B ~ census data & reportable diseaseGroup C ~ environmental monitoring & National Center for Health Statistics

Buzz Group pages 231-23542422. Informal Observational StudiesMay be triggered by any client seen by the nurseNurse has s suspicion about a clientInformal inquiries are made by the nurseMajor problems are revealed

Questions are raised and hypothesis suggested that may form the basis for larger studies

Data to support the need for such studies may be obtained from various sources of existing data

Sources of Data for Epidemiologic Study4343Scientific Studies:Carefully designed studies

Findings from studies used to develop or add to body of professional knowledgeSources of Data for Epidemiologic Study4444Research Process for an Epidemiologic Study1. 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.4545Nursing Process for Communicable Disease ControlAssessment: case identification, case finding; comprehensive; no assumptions; communitys need for surveillance or new/improved control programsNursing Dx: Analyze the data, formulate goalsPlanning: assisting with immunizations, symptom relief, controlling disease if present, limiting exposure, collaborationImplementation: service delivery; supervision of staff; agency functions; primary prevention education for future infections; record keeping and reportingEvaluation: Measuring the effectiveness of the program or treatment4646Infectious Diseases of BioterrorismAnthraxAcute bacterial disease that affects mainly the skin (cutaneous) or respiratory tract (inhalation)Case fatality: 520% for cutaneous, 100% for inhalationSmallpoxVariola virus transmitted person to personRisks associated with smallpox vaccination

4747Awareness of Bioterrorism Community health nurses must raise their awareness & preparedness of bioterrorismThese personnel should be knowledgeable about the consequences of biological terrorism because:They work in the community and are in a position of responsibility to educate the public and allay fearCorrect information must be provided to families, groups & aggregatesThey will need to help people in the decision-making process re need for immunization against possible terror attacks

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