Introduction to Epidemiology PDF

INTRODUCTION TO EPIDEMIOLOGY Our Lady of Fatima University College of Medical Laboratory Science Biostatistics and Epidemiology Epidemiology- Defined  Study of the distribution and determinants of health-related states among specified populations and the applicati...

INTRODUCTION TO EPIDEMIOLOGY Our Lady of Fatima University College of Medical Laboratory Science Biostatistics and Epidemiology Epidemiology- Defined  Study of the distribution and determinants of health-related states among specified populations and the application of that study to the control of health problems 2 Epidemiology Purposes in Public Health Practice Discover the agent, host, and environmental factors that affect health Determine the relative importance of causes of illness, disability, and death Identify those segments of the population that have the greatest risk from specific causes of ill health Evaluate the effectiveness of health programs and services in improving population health 3  Solving Health Problems Step 1 - Step 1 Step 1 - Data Surveillance; determine collection time, place, and person Step 2 Step 2 Assessment Inference Solving health problems Step 3 Step 3 Hypothesis Determine how and why testing Step 4 Step 4 Action Intervention Action 4 DISEASE CAUSATION 5 Theories of Disease Causation  Disease was due to evil spirits  Recovery was attributed to good spirits  Disease as a form of punishment  Control measures include offering sacrifices and “casting-out demons” Theories of Disease Causation Filth Theory “Bad air”  Associates disease with  was the cause of fever. the physical  Building huge fires can environment purify the air  Disease change with  Programs to remove seasons, climate, filth likewise put up to temperature, serve to advance overcrowding and filth community sanitation.  Diseases were due to poisonous substances and gases from the earth Theories of Disease Causation Germ or Bacteriological Theory  Koch confirmed Pasteur’s previous claims  Disease is due to microscopic forms of life  Opened the concepts of isolation and quarantine  Measures to destroy and remove the bacteriological cause such as disinfection , fumigation and general cleanliness  Bacteriology – explained the origins and spread of communicable disease Henle-Koch's postulates (1877,1882) Koch stated that four postulates should be met before a causal relationship can be accepted between a particular bacterial parasite (or disease agent) and the disease in question. These are: 1. The agent must be shown to be present in every case of the disease by isolation in pure culture. 2. The agent must not be found in cases of other disease. 3. Once isolated, the agent must be capable of reproducing the disease in experimental animals. 4. The agent must be recovered from the experimental disease produced. Theories of Disease Causation Concept of Multiple causation  Disease results from the interaction of multiple ecologic factors within a dynamic system made up of an agent of disease, host and the environment Models of Disease Causation MODELS OF DISEASE CAUSATION 11 The Web  States that effects never depend on single isolated causes but rather develop as the result of chains of causation  result of complex genealogy and antecedents 12 Web of Causation for the Major Cardiovascular Diseases Web of Causation for Myocardial Infarction Epidemiologic Lever  The host and agent are at the opposite ends of a hypothetical lever while the environment serves as the fulcrum  Based on biologic laws:  Disease results from an imbalance between disease agent and man  The nature and extent of the imbalance depends on the nature and characteristics of the host and the agent  The characteristic of the two are influenced considerably by the conditions of their environment 15 The Epidemiologic Lever Agent Host Environment  Host Agent Environment 17 The Epidemiologic Triangle Agent Host Environment ENVIRONMENTAL FACTORS OF DISEASE ENVIRONMENTAL FACTORS OF DISEASE 19 1. THE ENVIRONMENT – external to the host and in which the agent may exist, survive, or originate – physical, climatologic, biologic, social and economic – Physical: – water, humidity, geologic formations, etc – Social: – characteristics of a group of people 20  Environment – enhance or diminish survival of agent – serve to bring agent and host into contact – reservoir that fosters the survival of infectious disease agent 21 Reservoir - living organism or inanimate matter in which an infectious agent normally lives and multiplies on which the agent depends primarily for survival and reproduces itself in such manner that it can be transmitted to a susceptible host - Reservoir of infection - Physical environment - Animals or insects - Human beings (main reservoirs) 22 Human Reservoirs Cases (+) infection and (+) disease Carriers (+) infection but (-) disease 23 Animal reservoirs Zoonotic diseases infectious diseases of animals that can cause disease when transmitted to humans. - rabies - plague 24 The Agent Factor of Disease  Agent is any element, substance, or force whether living or non-living, the presence or absence of which can initiate or perpetuate a disease process. 25 Types of Agents  1. Non-living  2. Living 26 1. Non-living Agents 27 Non-living Agents  1. Physical and Mechanical - extremes of temperature, light, electricity, physical trauma 28 Non-living Agents  2. Chemicals 2.a Exogenous – poisons 2.b Endogenous – accumulation of toxic products of metabolism 29 Non-living Agents  3. Nutrients 3.a Deficiency Agents – anemia from iron deficiency 3.b Excess Agents- obesity from over- eating 30 2. Living Agents biological organism capable of causing disease TYPES  Bacteria: TB, shigellosis  Viruses and rickettsia: AIDS, hepatitis  Fungi: candidiasis, athlete’s foot  Protozoans: amoebiasis, giardiasis  Helminthes: schistosomiasis, ascariasis 31 Characteristics of Agents of Diseases  1. Inherent Characteristics  2. Characteristics directly related to man  3. Characteristics related to the environment 32 Inherent Characteristics  1. Physical Features - include morphology, motility, presence or absence of capsule, spore or cyst forms 33 Inherent Characteristics  2. Biologic Requirements - refers to the things needed by agent to survive - Ex. some are aerobic, anaerobic, capnophilic 34 Characteristics directly related to man  Infectivity  Pathogenicity  Virulence  Immunogenicity 35 1. Infectivity - the ability of an agent to invade and multiply in a host. e.g. infection of high infectivity: measles infection of low infectivity: leprosy  Infectivity is dependent on a number of factors including viability, portal of entry, susceptibility of the host, susceptible tissues and body defenses of the host. 37 2. Pathogenicity – ability to produce clinically apparent illness. - dependent on factors such as dosage, presence or absence of capsule, degree of toxigenicity, condition of the host 3. Virulence – severity of the reaction produced and measured in terms of fatality 39 4. Immunogenecity – infections ability to produce specific immunity. ex. measles produces lifelong immunity 40 Characteristics in relation to the environment  1. Reservoir  2. Sources of infection  3. Modes of transmission 41 Modes of Transmission  refer to the mechanisms by which an infectious agent is transported from reservoir to susceptible human host 42 Modes of Transmission  There are three modes of pathogen transmission:  Contact transmission  Vehicle transmission  Vector transmission 43 CONTACT TRANSMISSION  A host is exposed to infectious agents by making contact with the agent or items contaminated with the pathogen so it can reach a portal of entry into the host 44 Direct Contact Transmission  There is no intermediary between infected and uninfected individuals.  It encompasses such things as touching, kissing, and sexual interactions.  Diseases transmitted through direct contact include:  Hepatitis A  Staphylococcal infections  Sexually transmitted diseases. 45 Droplet Transmission  Droplet transmission is seen in the transfer of respiratory diseases such as influenza and whooping cough.  It can occur through sneezing, coughing, and even laughing. 46 Indirect Contact Transmission  Takes place through intermediates:  Tissues, Handkerchiefs  Towels  Bedding  Contaminated needles (the latter easily transferring HIV and hepatitis B).  Nonliving intermediates that act as the agents of transmission by indirect contact are referred to as fomites. 47 VEHICLE TRANSMISSION  Vehicle transmission involves pathogens riding along on supposedly clean components.  Examples of vehicles include:  Air  Food  Water  Blood  Bodily fluids  Drugs  Intravenous fluids 48 VEHICLE TRANSMISSION  Air is a difficult vehicle to control.  Dust uses air as a vehicle and can contain huge numbers of pathogens.  Microbial spores and fungal spores can also use air to travel from host to host. 49 VECTOR TRANSMISSION  Pathogens are transmitted by carriers, usually arthropods:  Fleas  Ticks  Flies  Lice  Mosquitoes 50 VECTOR TRANSMISSION There are two types of vector transmission:  Mechanical vector– pathogens are on vector’s body parts and are passively brushed off and onto the host  Biological vector – pathogens are within the vector and transmission to the host is through a bite 51 3. THE HOST  goes through chain of events leading from inapparent infection to a clinical case of the disease GRADIENT OF INFECTION - Range of infection, from inapparent to severe disease 52 the host  Severity of illness depends on resistance of the host (immunity level)  end result of infection -- complete recovery -- permanent disability/disfigurement -- death -- chronicity 53 Characteristics of the host Non-specific Defense Mechanisms  Skin  mucosal surface  Tears  Saliva  acid pH of gastric juice  phagocytes & macrophages  Age, nutrition status, genetic factors 54 Other concepts related to causation OTHER CONCEPTS RELATED TO CAUSATION 55 Necessary versus Sufficient Cause  Necessary Cause – Factor must be present for the disease to occur  it must invariably precede an effect  Sufficient Cause – Cause that inevitably initiates or produce an effect  includes “component causes” Any given cause may be necessary, sufficient, both, neither 56 Types of Causal Relationships  Necessary and sufficient – without the factor, disease never develops  With the factor, disease always develops (this situation rarely occurs)  Necessary but not sufficient – the factor in and of itself is not enough to cause disease  Multiple factors are required, usually in a specific temporal sequence (such as carcinogenesis)  Sufficient but not necessary – the factor alone can cause disease, but so can other factors in its absence  Benzene or radiation can cause leukemia without the presence of the other  Neither sufficient nor necessary – the factor cannot cause disease on its own, nor is it the only factor that can cause that disease  This is the probable model for chronic disease relationships HERD IMMUNITY immunity of a group or a community “resistance”of a group to invasion and spread of an infectious agent based on the immunity of a high proportion of individual members of the group important factor underlying the dynamics of propagated epidemics 58 NATURAL HISTORY OF THE DISEASE 59 NATURAL HISTORY OF DISEASE TWO PHASES  PREPATHOGENESIS  Phase before man is involved  Through interaction of agent, host and environmental factors, agent finally reaches man  PATHOGENESIS  Includes the success invasion and establishment of the agent in the host  From incubation period to production of detectable evidence of the disease process (Clinical Horizon), until it is interrupted by treatment Natural History of Disease  “Progression of a disease process in an individual over time, in the absence of treatment” --(CDC) STAGE OF SUSCEPTIBILITY  Pre-exposure period in the natural history of disease, in which the individual in the population is vulnerable or at risk to acquire the infection and/or amenable to get exposed to and be harmed by a health determinant.  During this stage, the individual in the population does not have the disease nor the infection; only the risk factors are present.  The susceptibility stage ends with the effective exposure. Pre-Pathogenesis Susceptibility EXPOSURE Adaptation Who is at Risk?  Risk factors  Poor health and nutrition  Lack of immunity  Behaviors that increase opportunity for exposure Adaptation  Failure leads to pathogenesis  Immediate response of the body  Immune system STAGE OF PRESYMPTOMATIC DISEASE (Sublinical stage)  The etiological factors (e.g. infectious agent, risk behaviours, environmental toxins) are present in the body and are causing pathological changes, but there are not yet any discernible signs or symptoms.  In this stage there is no manifest of disease but pathogenic changes have started to occur  The time required for the agent to establish itself, multiply and produce toxins Sub-clinical stages of disease Incubation period Latency period  Asymptomatic  Asymptomatic  Time between exposure  Time between exposure to onset of symptoms to causal factor and  Infectious diseases disease detection  **common in NCD CDC.G OV STAGE OF CLINICAL DISEASE  Refers to the period of time at the onset of signs or symptoms of the disease.  Sufficient end-organ changes have occurred so that there are recognizable signs or symptoms of disease  The outcomes of this stage may be recovery, disability or death.  It is important to subdivide this stage for better management of cases and for purposes of epidemiologic study  Morphologic subdivision or on functional or therapeutic considerations STAGE OF DISABILITY  The final stage in the natural history of disease concerns the outcome: recovery, disability or death.  Some diseases run their course and then resolve completely either spontaneously or by treatment  Any temporary or long term reduction of a person’s activities Pre- Pathogenesis Susceptibilit y EXPOSUR E Adaptation Pathogenesis Subclinical Clinical Outcome Levels of Prevention Primordial Before risk factors Primary Pre-pathogenesis Secondary Subclinical or very early clinical Tertiary Middle to late clinical pinter est Primordial Prevention  Prevent development of risk factors  Target: National Policies and Programs Mass Education Individual Education Primary Prevention  Prevent disease:  Reduction of risk factors  Immunization  Removal of harmful agents  Target: Secondary Prevention  Early detection  Prompt treatment  Cure disease at the earliest stage  Target: Tertiary Prevention  Complete treatment  Limit disability  Rehabilitation  Target: Classification of diseases  Method of grouping of diseases based on their specific features  Ensures universal criteria for diagnosing diseases  Usually dependent on current level of knowledge about the disease Classification of Diseases Classification Data Used Examples Clinical Signs and symptoms Cancer CVD Etiologic Presumed cause Tuberculosis AIDS Sources of Epidemiologic Data Sources of Epidemiologic Data WHO-HMN 2008  Considerations in Choosing the Source of Data  Research Objective  Data Quality  Sensitivity Issues  Logistics General Types of Data  Primary Data: collected by the researcher firsthand  Secondary Data: derived from another source that may have other objectives for collecting the data Data Sources according to Type of Data Primary Secondary  A. Queries  A. Computerized  Interviews bibliographic databases  Questionnaires  FGD  B. Surveillance data  Census  B. Observations  Registries  Direct  Hospital records  With tools  Insurance records Secondary: Census  Advantage  Disadvantage  Info on population  Small number of numbers and health questions that distributions by age, can be included sex and others  Allows small-area estimation and disaggregation like socio-economic status Secondary: Civil Registry  Primary purpose: establishment of legal documents as required by law  Major and most effective source of vital statistics  **Cause of death together with ICD Civil registry  Advantage  Disadvantage  Enables the routine  In low and lower- production of vital middle-income statistics essential for countries, civil improving health registry is weak or outcomes, as well as non-existent the provision of small-area data Civil Registry: Birth Statistics  Most visible evidence of a government’s existence of a person as a member of the society  Uses of birth certificate data:  Calculation of birth rates  Maternal conditions, length of gestation, birth weight, congenital abnormalities..  Problems: completeness of entries, unreliable data from the mother, neonatal defects undetected at birth Civil Registry: Death Statistics  Mortality data have the advantage of being almost totally complete because deaths are unlikely to go unrecorded  **Cause of Death  Immediate cause of death: final disease, injury, complication  Antecedent cause of death: intervening event between immediate and underlying cause of death  Underlying cause of death: disease that initiated chain of morbid events Civil Registry: Death Statistics  Uses of death certificate:  Calculation of mortality rates  Information on CoD  Problems:  Correctness of entries  Stigma associated with certain illnesses  Lack of standardization of diagnostic criteria  Change of coding for CoD over time Notifiable Disease Statistics  Reportable diseases  Selected for being epidemic-prone  Targeted for eradication or elimination  Subject to international health regulation  USES  Monitor progress towards disease reduction targets  Measure achievements of disease prevention activities  Identify hidden outbreaks or problems so that early action may be taken Notifiable Diseases  Category 1  Category 2  acute flaccid paralysis,  Acute blood diarrhea, anthrax, adverse event acute encephalitis, acute following immunization, hemorrhagic fever, human avian influenza, acute viral hepatitis, measles, meningococcal bacterial meningitis, disease, neonatal cholera, dengue, tetanus, paralytic diptheria, influenza-like, shellfish poisoning, leptospirosis, Malaria, rabies, SARS, Non-neonatal tetanus, outbreaks, clusters of pertussis, typhoid and diseases, unusual paratyphoid fever diseases or threats Population (Sample) Survey  Advantage  Disadvantage  Prime data sources  Less efficient in rare on risk factors events  Sampling error  Possible to generate  Estimates for local important data on the areas may not be links between health possible and socio-economic determinants Institution-based Surveillance Data Within the Health Sector Beyond the Health Sector  Case reporting  Food and agricultural  Morbidity and mortality records data  Occupational reports  Availability and quality of  Police records services  Services delivered and commodities provided  Resources Data Quality and Utility  Nature of the data  Vital statistics, registries, surveys  Availability of the data  Accessibility to the researcher  Completeness of population coverage  Representativeness  Vale and limitations  usefulness Data Privacy and Confidentiality  Privacy vs. Confidentiality ?  Republic Act 10173: Data Privacy Act of 2012  Executive Order No. 2 s. 2016: Freedom of Information Sensitive personal information (RA 10173)  Individual’s race, ethnic origin, marital status, age, political affiliations, etc.  Individual’s health, education, genetic or sexual life of a person, etc.  Issued by government agencies like SSS number, licenses, tax returns, etc. Data Sharing  Voluntary release of information by one investigator or institution to another for purposes of scientific research  Advantage: enhancement of knowledge  Issues:  Loss of control over intellectual property  Loss of privacy and confidentiality of the research subject Data Linkage  Joining data from two or more sources  Requires interoperability of data sources  Talk with each other  Use of common identifying features to connect data records on a single individual THANKYOU! 101