Final Exam Review - Epidemiology PDF

11/29/18 FINAL EXAM REVIEW INTRODUCTION TO NSG 522: Applied Epidemiology and EPIDEMIOLOGY Biostatistics for Nursing Practice...

11/29/18 FINAL EXAM REVIEW INTRODUCTION TO NSG 522: Applied Epidemiology and EPIDEMIOLOGY Biostatistics for Nursing Practice Rush University, College of Nursing What is Epidemiology? Core Epidemiological Functions Epidemiology is… 1. Surveillance 2. Field investigations “The study of the distribution and determinants of heath- 3. Analytic studies related states or events in specified populations, and the 4. Evaluation application of this knowledge to the control of health 5. Linkages problems.” 6. Policy CDC, 2006 Epidemiology is a Quantitative Science 5 W’s of Epidemiology Epidemiology is a quantitative science What? When? Measurement is an essential feature of epidemiology Where? Who? Measurement focuses on Why? - Distribution of health-related states and events - Determinants of health-related states and events Epidemiology is a story about health related states and events supported with data 1  11/29/18 Epidemiology Descriptive Epidemiology Two components of epidemiology Describes the WHEN, WHERE and WHO - Descriptive - Time - Analytic - Place - Person Descriptive epidemiology studies the DISTRIBUTION of health related states and events Descriptive epidemiology studies the FREQUENCY and PATTERN of health related states and events Analytic Epidemiology Descriptive vs. Analytic Epidemiology Analytic epidemiology Descriptive epidemiology describes the - Why-- Cause and Effect - Distribution of health-related events - Frequency and pattern of events - Analytic epidemiology quantifies the association between - The ‘who, where, and when’ exposures and outcomes to determine causal - The ‘person, place, and time’ relationships - The ‘why’ examines potential etiologies (helpful or harmful) for the health-related event Analytic epidemiology describes the - The ‘why’ explains the causes of the health-related state - Determinants of health-related events or event - The ‘why’ - Analytic epidemiology studies the DETERMINANTS of - The ‘cause(s)’ health related states and events The Role of the CDC DETERMINANTS OF HEALTH 2  11/29/18 Determinants of Health Biological Sources of Disease Biological Congenital Environmental Hereditary Social Infectious Health behaviors Inflammatory Metabolic Nutritional Tumors Vascular Environmental Sources of Disease Social Determinants of Health Allergens Chemical exposures Infectious organisms Nutrition Physical agents Trauma Health Behaviors Nutrition Physical activity Rest and relaxation MECHANISMS Tobacco use Alcohol use OF Illicit substance use Immunizations DISEASE CAUSATION 3  11/29/18 Multicausality The ‘Causal Pie’ Model Causative agent or event Every causal mechanism involves the joint action of a Characteristics of the person multitude of component causes Characteristics of the environment The etiology of all diseases is multifactorial, even with a Presence of preventative factors simple infectious disease Action of catalysts or additive factors Mediating and moderating factors Some disease have very complex etiologies (e.g., Interaction between the factors cardiovascular disease) Bradford Hill Criteria for Causation Strength of association Consistency Specificity Temporal relationship MODELS OF Biological gradient Plausibility DISEASE CAUSATION Coherence Analogy Experimental evidence Etiology of Disease Epidemiological Triad or Triangle Occurrence of disease can be understood using 3 models: - Epidemiological Triad or Triangle - BEINGS Model - Web of Causation 4  11/29/18 BEINGS Model of Disease Causation Web of Causation B – Biological, Behavioral E – Environmental I – Immunological N – Nutritional G – Genetic S – Services, Social, Spiritual Spectrum of Disease Describes the severity of disease Can vary from mild to fatal SPECTRUM AND NATURAL HISTORY OF DISEASE Natural History of Disease Stage of Susceptibility Natural history of a disease describes the progression of the disease process over time in an untreated individual Describes the stages of disease - Stage of susceptibility - Stage of preclinical, subclinical, presymptomatic, or latent disease - Stage of clinical disease - Stage of recovery, disability, or death 5  11/29/18 Stage of Subclinical Disease Stage of Clinical Disease Not apparent or asymptomatic Onset of symptoms Pathological changes occur Diagnosis usually occurs during this stage Pathology may be detected by screening Incubation period for infectious diseases Latency for chronic disease Stage of Recovery, Disability, or Death LEVELS OF PREVENTION Primary Prevention Secondary Prevention Used during the stage of susceptibility Used during the preclinical (subclinical, presymptomatic, Protects against the disease latent) and early clinical stages of disease - Place the host in good health Early detection and prompt intervention to control the - Protects against disease or other health-related disease and minimize or eliminate complications events (e.g., immunization) - Public health measures 6  11/29/18 Levels of Prevention and the Tertiary Prevention Stages of Disease Stage of susceptibility Used during the advanced stage of clinical disease or - Primary prevention when disability has occurred Measures aimed at reducing the long term impact of Stage of preclinical, subclinical, presymptomatic, or latent disease and disability disease - Secondary prevention Stage of clinical disease - Secondary prevention during early part of stage - Tertiary prevention during more advanced disease Stage of recovery, disability, or death - Tertiary prevention Prevention and the Natural History of Disease COMMUNICABLE DISEASES Communicable Disease Chain of Infection The ability of a disease to Reservoir - Be transmitted from one person to another -or – Portal of exit - To spread through the population is called Transmission communicability - Direct - Indirect - Airborne Portal of entry Susceptible host 7  11/29/18 Reservoir Portal of Exit Reservoir Portal of exit from the reservoir - Habitat in which the agent grows and lives - Respiratory tract - Blood Reservoirs can be - Semen - Human - Other body fluids - Animal - Crossing the placenta (mother-to-fetus) - Invertebrates (insects, arachnoids) - Blood sucking mosquitos - Environment Mode of Transmission Portal of Entry Direct transmission - Direct contact (kissing, sexual intercourse, soil contact) Portal of entry into the host - Respiratory tract Indirect transmission - Mouth - Vehicleborne (food, water, bedding, instruments) - Break in the skin or mucous membrane - Vectorborne (mosquitos, fleas, ticks) - Surgical sites - Catheters Airborne transmission - Droplet (direct mode of transmission) - Droplet nuclei (indirect mode of transmission) Susceptible Host Susceptible host - Immune status - Overall health PREVENTION - Nutritional status AND CONTROL OF INFECTION 8  11/29/18 Primary Prevention for Infection Active and Passive Immunity Used during the stage of susceptibility Active immunity Protects against the disease - Body produces its own antibodies in response to having been vaccinated or having a specific disease Includes activities pathogen invade the body - Eliminate or sanitize the reservoir - Eliminate or cover the portal of exit Passive immunity - Eliminate or cleanse the transmission mode - Administration of immune globulin - Cover or filter the portal of entry - Transplacental transfer of immune globulins to the - Place the host in good health and immunize when fetus available - Transfer of antibodies and other immunoprotectant in human milk Herd Immunity Cocooning Viewed as the resistance a population has to the invasion Used to protect infants from communicable diseases and spread of an infectious disease Only family and friends who are fully immunized are Based on the notion that if a population or group is allowed to be around the infant mostly protected from a disease by immunizations (85% or more), then the chance of a major epidemic occurring is reduced Host-Related Control and Prevention Isolation - Used for persons who are known to be ill with a contagious disease - Used in inpatient settings (hospitals or nursing homes) DESCRIPTIVE - State laws as well as accrediting organizations require one or two beds to be designated and as EPIDEMIOLOGY isolation beds Quarantine - Used for persons who have been exposed to a contagious disease but may or may not become ill 9  11/29/18 Using Tables to Describe Person Descriptive Epidemiology Descriptive epidemiology describes the - Frequency of events - Pattern of events - Who (person) - Where (place) - When (time) Using a Population Pyramid to Describe Person Using Maps to Describe Place Using Event Timelines to Describe Time HEALTH SURVEILLANCE 10  11/29/18 Public Health Surveillance Health Indicator Defined as the “ongoing, systematic collection, analysis, and interpretation of health-related data essential to Markers of health status information for the planning, implementation, and of - Physical or mental illness public health practice, closely integrated with the timely - Impairments or disabilities dissemination of these data to those responsible for - Social well being prevention and control” (CDC) - Service provision - Resource availability Public health surveillance uses data to monitor health problems to facilitate their prevention or control Information gained from surveillance can be used for - Planning disease control and prevention programs - Policy-making Notifiable Diseases in the United States Many infectious disease must be reported so that appropriate control measures can be implemented Other diseases are also reported Federal and state mandated reporting MEASURES OF Notifiable diseases are those of considerable public health importance because of their seriousness. DISEASE - Cause serious morbidity or death OCCURANCE - Have the potential to spread - Can be controlled with appropriate intervention Measures of Disease Occurrence Ratios Counts Ratios compare two things - Number (n) - Frequency (f) Divide the numerator by the denominator Ratios Proportions Expressed as X/Y or X:Y Percentages Rates Numerator may or may not be part of the denominator The numerator and denominator may or may not be related 11  11/29/18 Proportions (p) Percentages (P) Numerator is always a part of the denominator Numerator is always a part of the denominator Just a proportion multiplied by 100!!! Calculated as p= A e.g., 1/8 =.125 = 12.5% A+B Calculated as P = A * 100 A+B Usually calculated as a decimal e.g., 1/8 =.125 Rates Frequency of an event in a population in a specified period of time Population is always specified VITAL Time period is always specified STATISTICS Vital Statistics Mortality Three major categories of vital statistics A mortality rate is a measure of the frequency of - Mortality occurrence of death in a defined population during a specified interval. (CDC, 2006) - Morbidity - Natality Deaths during a given time period × 10n* Size of the population in which the deaths occurred * (usually 1,000 or 100,000) CDC, 2006 12  11/29/18 Crude (All Cause) Mortality Rate Infant Mortality Rate The crude mortality rate is the mortality rate from all causes of death for a population Infant mortality rate Also called the “All Cause” Mortality Rate - Deaths of infants < 1 year of age - Denominator is number of live births in the given time Example period - In 2003, there were 2,419,921 deaths in the USA - Live birth has a specific definition - The estimated population was 290,809,777 - Per 1,000 live births - The crude mortality rate was 2,419,921 ⁄ 290,809,777 × 100,000 = Single most widely used health indicator to compare nations 832.1 deaths per 100,000 population Neonatal Mortality Rate Maternal Mortality Rate Neonatal mortality rate Maternal mortality rate - Deaths of infants < 28 days of age - Deaths of women due to pregnancy related causes - Denominator is number of live births in the given time during pregnancy or during the first 42 days after period pregnancy termination, regardless of the duration of - Per 1,000 live births the pregnancy - Denominator is number of live births in the given time period - Per 100,000 live births Morbidity Incidence and Prevalence A morbidity rate is a measure of the frequency of Incidence and prevalence are the two major measures of occurrence of disease or injury in a defined population during a specified interval. disease frequency Cases during a given time period × 10n* Size of the population in which the cases occurred * (usually 1,000 or 100,000) 13  11/29/18 Prevalence Prevalence Prevalence refers to the status of disease, not the onset Prevalence is calculated as a proportion Prevalence measures the frequency of a disease at a Prevalence = particular point in time Number of individuals who have a disease at a particular point in time Total population at risk at the specified time Prevalence measures all cases (old and new) at a specified period of time Point prevalence = assessed at one specific point in time Period prevalence = assessed during a certain period Incidence Incidence Proportion Incidence measures the rate at which people without a disease develop the disease during a specified period Incidence Proportion = Number of new cases of a disease in a specified time period Incidence is a measure of the onset of disease Population at risk of the disease at the start that time period Incidence measures the appearance of disease Also called - Risk Incidence means new - Attack rate - Probability of developing a disease Incidence Rate Incidence Rate = Number of new cases of a disease in a specified time period Time that each person was observed, totaled for all persons EPIDEMIOLOGIC Also known as “”Person-Time Rate” STUDY DESIGNS Most accurate estimate of risk More difficult to calculate Accounts for incomplete data 14  11/29/18 Levels of Evidence Systematic Reviews: Meta-Analyses Study of studies Systematic reviews Method used in Cochrane Reviews and AHRQ Reviews Randomized controlled trials Very powerful methodology Stringent criteria for inclusion in the analysis Nonrandomized trials Quantitative analysis to combine and compare results of Cohort studies the studies Case-control studies Cross-sectional studies Case reports and case series Opinion, experience, and theory Study Designs in Epidemiology Study Designs in Epidemiology Prospective Experimental studies - Randomized controlled trails - Randomized trials - Quasi-experiments (non-randomized trials) - Non-randomized trials (quasi-experiments) - Prospective cohort studies Observational studies Retrospective - Cohort studies - Retrospective cohort studies - Case-control studies - Case-control studies - Cross-sectional studies Cross-sectional Prospective Study Designs Prospective Cohort Studies Randomized clinical trials A group (cohort) of disease-free individuals is identified at - Randomization to treatment groups one point in time and then followed over a period of time to determine whether whether the outcome (disease) - Control of the intervention occurs Non-randomized clinical trials (quasi-experiments) - No randomization to treatment groups - Comparison group may be different from the intervention group - Control of the intervention 15  11/29/18 Retrospective Cohort Studies Case-Control Studies Retrospective study that have a historical perspective Retrospective study design - Requires access to information about the subjects Studies people who already have the disease and looks before the exposure to disease causing factors and backward at exposures the onset of disease occurs - Often able to accomplish this when there are Two groups of individuals are studied comprehensive medical records - A group that has the disease under study (cases) - A group that does not have the disease under study Also known as historical cohort studies (controls) Their health information is then examined to determine whether there are risk factors that may be related to their current disease Cross-sectional studies A population is studied at a single point in time Participants are asked about their current disease state and their exposures to certain factors RISK: Also known as prevalence studies WHAT IS IT? Weakest study design Calculation of Risk Absolute and Attributable Risk The probability that an event will occur Absolute Risk - The overall incidence of the disease in a specified Risk is calculated as a proportion population - Calculated the same as the incidence proportion Risk is the same as the incidence proportion Risk is presented as a probability and can vary from 0 to 1.0 Attributable Risk - The amount of disease associated with a causative Risk = Number of people who get the disease during a designated period factor in a specified population Population of interest at the start of the designated time period 16  11/29/18 Measures of Association Relative Risk (RR) Measures of association are used to compare the occurrence of disease in one group with the occurrence Relative risk is a measure of association between the of disease in another group exposure to a particular factor and the risk of a particular disease or outcome Commonly used measures are - Risk Ratio or Relative Risk (RR) Can only be calculated from prospective studies - Odds Ratio (OR) Relative Risk = Incidence rate among the exposed Incidence rate among the non-exposed Odds Ratio Interpretation of the Risk and Odds Ratios Is used to estimate the Relative Risk when the RR cannot RR or OR = 1 be calculated - Risk/Odds in the exposed is equal to the risk/odds in the non-exposed group Used in case-control and other retrospective studies RR of OR > 1 Odds ratio = The odds that a case was exposed - Risk/Odds in the exposed group is greater than the The odds that a control was exposed risk/odds in the non-exposed group RR or OR < 1 - Risk or Odds in the exposed group is less than the risk/odds in the non-exposed group Risk Ratios: Confidence Intervals Confidence Intervals Risk ratios and odds ration are estimates are the actual If the CI includes 1, there is not a difference between the population risk and odds ratios exposed and unexposed groups Confidence intervals are calculated for risk and odds - RR or OR = 1.5 [CI: 0.8, 2.2] ratios If the confidence interval includes 1, the risk ratio is not If the CI does not include 1, there is a difference between statistically significant and that means the exposure did the groups not significantly increased or decreased the risk of - RR or OR = 1.5 [CI: 1.1, 1.9] disease If there is a difference between the groups, you have to If the confidence interval does not include 1, the risk ratio determine whether the difference is increased or is statistically significant and that means the exposure decreased significantly increased or decreased the risk of disease 17  11/29/18 Confidence Intervals The exposure group (RR) or the cases (OR) are always in the numerator and the comparison (non-exposed or control) groups are always in the denominator If the RR or OR is greater than 1 and the CI does not HEALTH include 1, that means there is a greater risk in the exposed group RR or OR = 3.3 [CI: 2.0, 4.6] SCREENING If the RR or OR is less than 1 and the CI does not include 1, that means there is a reduced risk in the exposed group OR = 0.72 [CI: 0.54, 0.92] Health Screening Screening as Secondary Prevention Screening is used to promote detection of diseases in Health screening activities are used to identify disease their earliest stages, when treatment has the greatest during the preclinical (subclinical, presymptomatic, latent) chance of working, in order to reduce morbidity and stage of disease mortality Stage of Subclinical Disease Not apparent or asymptomatic Pathological changes occur and some can be detected by screening Incubation period for infectious diseases CHARACTERISTICS Latency for chronic disease OF SCREENING TESTS 18  11/29/18 Sensitivity Sensitivity Probability that a person with the disease will test People in the Population of Interest positive for the disease (true positive) Screening Test Disease Present No Disease The ability of the test to correctly identify those with the disease A Positive Test True Positive B Probability of correctly identifying the disease C Negative Test False Negative D Sensitivity = A / (A+C) Specificity Specificity Probability that a person who does not have the disease People in the Population of Interest will test negative for the disease (true negative) Screening Test Disease Present No Disease The ability of the test to correctly identify those without the disease B Positive Test A False Positive D Negative Test C True Positive Specificity = D / (B+D) Positive Predictive Value Positive Predictive Value Probability that a person who has a positive test actually People in the Population of Interest has the disease Screening Test Disease Present No Disease Proportion of people with a positive test result who have A B Positive Test the disease True Positive False Positive C D Negative Test False Negative True Negative Positive Predictive Value = A / (A+B) 19  11/29/18 Negative Predictive Value Negative Predictive Value Probability that a person who has a negative test does People in the Population of Interest not have the disease Screening Test Disease Present No Disease Proportion of people with a negative test result who do A B not have the disease Positive Test True Positive False Positive C D Negative Test False Negative True Negative Negative Predictive Value = D / (C+D) INVESTIGATION OF AN TERMINOLOGY OUTBREAK Cases: Definitions Cases: Definitions Case Secondary cases - An individual who has the disease, disorder, injury, - Cases that became ill after the disease was health behavior, or health event of interest introduced into the population and become infected from the primary case Primary case - First case of the disease or condition or behavior Suspect case - An individual who has all of the signs and symptoms of Index case a disease or condition, yet not diagnosed - First case brought to the epidemiologists attention (not necessarily the primary case) Confirmed - All criteria are met 20  11/29/18 Terminology Epidemic, Outbreak, and Pandemic Endemic Epidemic - Amount of disease usually present in a community - An increase in the number of cases above what is expected in the population in that area Hyperendemic Outbreak - Persistent high levels of disease - An epidemic but in a limited geographic area Sporadic Pandemic - Occurs infrequently and irregularly - Epidemic that has spread over several countries or continents Spread of Epidemics Common source - Attributed to a specific source - Point sources - Intermittent sources - Continuous sources STEPS IN AN Propagated INVESTIGATION - Transmitted from person to person Mixed epidemic - Starts with a common source - Then spread by person-to-person contact Steps in a Field Investigation Establish Criteria for Case Identification 1. Establish the existence of an epidemic (or outbreak) 2. Confirm the diagnosis Standard clinical criteria (what) 3. Establish criteria for case identification Loose case definition vs. strict case definition 4. Search for missing cases A case may be further characterized by 5. Count cases - Who 6. Orient the data according to person, place, and time 7. Classify the epidemic - Where 8. Determine who is at risk of becoming a case - When 9. Analyze the data 10. Formulate a hypotheses 11. Test hypotheses 12. Develop reports and inform those who need to know 13. Execute control and prevention measures 14. Administration and planning activities 21  11/29/18 Case Definitions Case Definitions Count Cases Examine the Data by Person, Place, and Time Person - Inherent characteristics (age, race/ethnicity, sex) Use standard descriptive statistics - Acquired characteristics (immunity or marital status) Exposure status and disease frequency need to be - Activities (occupation, leisure, use of medications) determined and compared with the appropriate at-risk - Conditions (socioeconomic state, access to health care) Place population - Residence - Birthplace - Place of employment - School district, hospital unit - Country - State - County - Census tract - Street address - Map coordinates Time - Epidemic curve Classify the Epidemic Analyze the Data Use an epidemic curve to classify the epidemic Descriptive analysis - Common source - Descriptive statistics - Propagated Graphic display - Mixed - Spot Map - Epidemic Curve Testing for relationships - Associations - Correlations 22  11/29/18 Implement Control and Prevention Measures Immunization programs Risk factor prevention Behavior change programs Good Luck! 23