Epidemiology Handout PDF

EPIDEMIOLOGY  From the Greek word “epos” which means upon and “demos” which means people  “Study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the prevention and control of health problems.”...

EPIDEMIOLOGY  From the Greek word “epos” which means upon and “demos” which means people  “Study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the prevention and control of health problems.” (Last, 2001)  Is the study of all factors that affect the health and cause diseases in populations  Known as the “backbone of disease prevention” USES of Epidemiology I. ASSESSMENT OF HEALTH STATUS OF THE POPULATION - used to describe the health status of the population groups to determine priority health programs based on identified community health problems - such issues/concerns may be existing diseases or health-related behaviors that lead to poor health II. NATURAL HISTORY OF DISEASES - epidemiology gives a picture of the natural history of diseases in individuals and groups. - It describes the subclinical changes to signs and symptoms of the clinical disease until its resolution to recovery or death Stages of Infection  Exposure – the moment a pathogen enters a susceptible host - the pathogen will invade and target organ and tissue and multiply there - the body will start its immune system response  Latent Period – period between exposure and infection without clinical symptoms or infection in the host  Incubation Period – period between exposure and onset of clinical symptoms - host may become infectious  Infectious Period – time during which the host can infect another susceptible host  Noninfectious Period – period when the host’s ability to transmit the disease Levels of disease Occurence (Centers for Disease Control – CDC) 1. Sporadic – refers to a disease that occurs infrequently or irregularly 2. Endemic refers to the constant presence and/or usual prevalence of a disease of a population in a geographic area 3. Hyperendemic – refers to persistent, high levels of disease occurrence 4. Epidemic – refers to an increase, often sudden in the number of cases of a disease above what is normally expected in that population in that area 5. Outbreak – carries the same definition of epidemic, but is often used for a more limited geographic area 6. Cluster – refers to an aggregation of cases grouped in place and time that are suspected to be greater than the number expected even though the expected number may not be known 7. Pandemic – refers to an epidemic that as spread over several countries or continents, usually affecting a large number of people III. MODELS OF DISEASE CAUSATION – epidemiology helps by having models of disease causation specifying the risk factors and the conditions that surround them that lead to disease or poor health Three models of disease causation 1. Epidemiologic Triad or Triangle  traditional model  disease results from the interaction between the susceptible host and the agent in the environment that supports transmission of the agent from a source to that host Triad talks of the three components of the disease process  HOST – any organism that harbors and provides nourishment for another person or to a parasite  AGENT – refers to infectious microorganism or pathogen present for disease to occur - could also be chemical contaminants or physical forces  ENVIRONMENT – sum total of all the external conditions 2. Iceberg Principle – shows the disease situation where the problem is subclinical, unreported or hidden from view  only the “tip of the iceberg” is known  e.g. resulting deaths from suicides or reported cases of AIDS  Public Health Goal: to find out through screening and early detection those who are exposed or affected so that proper interventions can be done 3. Web of Causation – shows the relationship between different multiple factors that contribute to the cause of a disease  proposes that diseases are caused by the interaction between genetic factors and environmental factors (biological, chemical, physical, psychological, economic or cultural)  Can be microorganisms, genetic abnormalities, socio-economic factors and environmental factors  personal behaviors also affect this interaction and interventions can be done through health promotion IV. SCREENING AND SURVEILLANCE – important in identifying risk factors and monitoring health and disease conditions in the population  evidence from surveillance are often used to develop screening programs, prevention and treatment policies  SCREENING  is the active search or process of detection for disease or disorders among apparently healthy people  primary aim is to identify risk factors and diseases in their earliest stage  SURVEILLANCE  is the systematic, on-going and analytic process of monitoring to scrutinize disease condition  involves investigating the distribution and possible causes of diseases and conditions within the population  information from this inform planning and improving health services and understanding the factors that contribute towards disease, as well as the long-term effects of these diseases Surveillance program categories  EVENT-BASED – are for rapid detection, notification, verification and assessment of public health events such as clusters of diseases, rumors of unexplained deaths  INDICATOR-BASED – are routine reporting of cases of disease such as notifiable disease surveillance systems V. LEVELS OF PREVENTION IN THE CONTEXT OF EPIDEMIOLOGY  public health focuses on health promotion and disease prevention  epidemiologic methods help in measuring the outcomes of strategies Levels of Prevention 1. PRIMORDIAL PREVENTION  seeks to prevent at a very stage, even before the risk factor is present  activities that promote healthy lifestyle and avoiding the development of behaviors and exposure patterns that contribute to increased of disease 2. PRIMARY PREVENTION  prevention through the control of exposure to risk factors before disease development  Health Promotion Activities – action designed to promote healthy lifestyle and environment  Health Protection Activities – aimed at reducing the risk of specific diseases 3. SECONDARY PREVENTION  is the application of available measures to detect early the disease or health condition before the onset of signs and symptoms 4. TERTIARY PREVENTION  is managing the disease after the diagnosis to slow or stop disease progression and limit disability or complications VI. EVALUATING INTERVENTIONS – epidemiological methods are also used in evaluating the effectiveness and efficiency of interventions 1. Population-Based Approach Interventions attempt to change socio-cultural or structural factors in the community, cities or even at the country level 2. High-Risk Approach Interventions targeting those persons who are likely to have increased incidence of a disease based on the presence of risk factors TYPES OF STUDIES IN EPIDEMIOLOGY Two Major Study Designs 1. Observational/non-experimental  Descriptive Observations – the who, what, where and when of a disease or a health-related event  Analytic Observation – the how of a disease or health-related event 2. Experimental - include randomized controlled trials, field trials and community trials OBSERVATIONAL/NON-EXPERIMENTAL EPIDEMIOLOGY  Descriptive Epidemiology - focuses on describing disease distribution by characteristics relating to time, place, and people - done through review of records, routine data collection, or ecological surveys - examines factors – age, sex, education, socioeconomic status, or availability of health services - may include information on behavior - evaluates frequency and pattern by examining the person, place, and time in relationship to health events - Patterns are described by tabulations or summaries of surveys  Analytical Epidemiology - aims to understand the quality and the amount of influence that determinants have on the  occurrence of disease or health-related event - Attempts to explain and predict the state of a population’s health - usually done by group comparisons - It summarizes the relationship between exposure and disease incidence by comparing two measures of disease frequency TYPES OF ANALYTICAL EPIDEMIOLOGY 1. Cross-Sectional Study – examines the relationship between health problems and other variables of interest as they exist in a defined population at one particular time - used to get baseline data, determine the magnitude of the health problem 2. Cohort Studies - a population with known levels of exposure to potential causative and protective factors is recruited and followed over time to determine who gets and who does not get the disease(s) of interest 3. Case-Control Study - is a retrospective study - subjects are selected based on the their disease or health condition (Case Group) are compared with subjects who are negative or have no disease or health condition (Control Group) EXPERIMENTAL EPIDEMIOLOGY  uses an experimental design or model to confirm a causal relationship suggested by observational studies  test a hypothesis about a health problem, disease or disease treatment in a group of people Three types of experimental epidemiology 1. Randomized Control Trials (RCT)  experiments with patients as subjects to evaluate a potential cure for a disease and prevent death and disability  used for testing new interventions or drugs  results are used to assess the effectiveness of the intervention, particularly the extent to which the intervention or drug does patient more good than harms 2. Field Trials  experiments done in the field involving subjects free of the disease or health condition but at high risk of contracting them  intervention is tested whether it reduces the risk of developing the disease or condition  cost more because they require more subjects and necessitates visiting subjects in their home, school or work place 3. Community Trials  extension of field trials involving the whole community as the unit of assignment  intervention can be evaluated by involving entire communities who were assigned the water treatment