Basic Epidemiologic Concepts and Principles Notes PDF

11 Oct 2022 Basic Epidemiologic I. DEFINITION OF EPIDEMIOLOGY...

11 Oct 2022 Basic Epidemiologic I. DEFINITION OF EPIDEMIOLOGY II. ETIOLOGY AND NATURAL HISTORY OF DISEASE A. Stages of Disease Concepts and B. Mechanisms and Causes of Disease C. Host, Agent, Environment, and Vector Presentation D. Risk Factors and Preventable Causes Principles 1. BEINGS Model Outline III. ECOLOGICAL ISSUES IN EPIDEMIOLOGY A. Solution of Public Health Problems and Unintended Creation of New Problems 1. Vaccination and Patterns of Immunity J O E R I Z P. V E L I G A N I O , R N , M D , M P M , D P B A 2. Effects of Sanitation P a r t- t i m e Fa c u l t y Section of Biostatistic s and Epidemiology 3. Vector Control and Land Use Patterns University of Southern Mindanao 4. River Dam Construction and Patterns of Disease Co l l e g e o f M e d i c i n e B. Synergism of Factors Predisposing to Disease 1 2 What is Epidemiology? Epidemiology – factors that determine the occurrence and IV. CONTRIBUTIONS OF EPIDEMIOLOGISTS A. Investigating Epidemics and New Diseases distribution of disease Presentation B. Studying the Biologic Spectrum of Disease C. Surveillance of Community Health Interventions Greek Roots: Outline D. Setting Disease Control Priorities E. Improving Diagnosis, Treatment, and Prognosis of Clinical Disease epi – “upon” demos – “people” or “population” F. Improving Health Services Research G. Providing Expert Testimony in Courts of Law logos – “discussion” or “study” Basic science of public health 3 4 1  11 Oct 2022 What is Epidemiology? What is Epidemiology? Methods to study disease, injury and clinical practice Classical Epidemiology – population-oriented, studies community origins of health problems; discovering risk factors Collection of data on an ENTIRE POPULATION Syndromic Epidemiology Approached by the following four levels: Clinical Epidemiology – use similar research designs and statistical 1. Submolecular or molecular level tools but study patients in health care settings; to improve 2. Tissue or organ level prevention, early detection, diagnosis, treatment, prognosis, and 3. Level of individual patients care of at risk or w/ the disease 4. Level of populations 5 6 What is Epidemiology? Etiology and Natural History of Disease Infectious Disease Epidemiology – depended on laboratory support Etiology – the cause or origin of a disease or abnormal condition Chronic Disease Epidemiology – depended on complex sampling Natural History – the way a disease progresses in the absence of and statistics medical or public health intervention Overlap seen w/ increased use of molecular markers and chronic Stages, mechanisms and causes of disease determine how and statistical analyses when to intervene Many illnesses may be regarded as both Goal is to alter the natural history of a disease in a favorable way 7 8 2  11 Oct 2022 Stages of Disease and Levels of Prevention Mechanisms and Causes of Disease Predisease Stage – before the disease process begins, early intervention Biologic mechanisms may avert exposure to agent of disease preventing disease process from starting – primary prevention Social causes Latent Stage – disease process has already begun but is still Behavioral causes asymptomatic, screening for disease and appropriate treatment may prevent progression to symptomatic disease – secondary prevention Environmental causes Symptomatic Stage – disease manifestations are evident, intervention may slow, arrest or reverse progression – tertiary prevention 9 10 Host, Agent, Environment, Risk Factors and Preventable Causes and Vector Subject of much epidemiologic research Figure 1-1 Factors involved in Majority of cancers are preventable, caused by extrinsic factors natural history of disease. Extrinsic factors, misinterpreted to man-made chemicals, but included viral infections, nutritional deficiencies/ excesses, reproductive activities, and others First method: % of individuals who have identifiable, preventable causes, added to determine total % of cancers w/ identifiable causes Second method: annual age and gender-specific cancer incidence in countries w/ lowest rates then maintain disease detection (presumably lower prevalence of risk factors) 11 12 3  11 Oct 2022 “B”-Biologic and Behavioral Factors Biologic Factors - E.g. Gender, Age, Weight, Bone density BEINGS Human behavior – E.g. Cigarette Smoking, HIV Spread (Unprotected Sexual Intercourse vs. Sharing of syringes among IV Acronym drug users), Excessive Alcohol Intake, Drug Use, Driving while intoxicated, Homicide/ Suicide B OX 1-1 CATEGORIES OF P REVENTAB L E CAUS E OF DIS EAS E 13 14 “E”- Environmental Factors “I”- Immunologic Factors Describe patterns of disease in the affected population, develop Herd immunity – when vaccine diminishes an immunized person’s and test hypotheses about causal factors, and introduce methods to ability to spread the disease  reduced disease transmission prevent further cases of disease Immunodeficiency – maybe caused by genetic factors E.g. Legionella pneumophila, Lyme disease Transient – noted after some infections (e.g. Measles) and after administering certain vaccines Avoided in seriously malnourished, cancer chemo, long-term corticosteroids 15 16 4  11 Oct 2022 “G”- Genetic Factors “N”- Nutritional Factors Genetic epidemiology – possible interaction of various genotypes w/ environmental, nutritional, behavioral factors, and pharmaceutical treatments Dietary variations – most important factors producing differences in disease Incidence of non-inherited disease is decreasing, ability to identify genetic rates diseases has improved Denis Burkitt (Burkitt’s Lymphoma) – Genetic screening – important in identifying problems in newborns (PKU, critical role played by dietary fiber in Congenital hypothyroidism); in the future identifying high risk for specific problems or responding well or poorly to specific drugs good health: cross-cultural studies Screening for susceptibility genes – ethical concerns about potential problems (medical insurance carriers hesitations) 17 18 “S”- Services, Social Factors, and Spiritual Factors “S”- Services, Social Factors, and Spiritual Factors Medical care services may be beneficial but can also be dangerous Effects of social and spiritual factors – less intensively studied Better resist noxious stressors when receiving social support from other Iatrogenic disease – disease induced inadvertently by tx or members of same species diagnostic Strong religious faith, meditation and massage = better health and QoL E.g. >50% of healthy women w/ annual screening mammography in 10 Mormons (prohibit vices) and Seventh-Day Adventists (encourage vegan): yr-period: at least 1 mammogram (suspicious but do not have Ca) lower than average adjusted death rates from common lifestyle disease and cancer Importance of having meaning and purpose in life = alleviate stress and improve coping 19 20 5  11 Oct 2022 Solution of Public Ecological Issues in Epidemiology Health Problems Regarded their field as “human ecology,” “medical ecology,” or and Unintended “geographic medicine” Creation of New Problems Important characteristic of epidemiology is ecological perspective People seen as members of communities in a social context Disease patterns vary greatly from one country to another Types and rates of diseases in a country indicates the standard of living, lifestyle, predominant occupations, climate, among other factors 21 22 Vaccination and Diphtheria Patterns of Immunity Vaccine-produced immunity decrease over time Figure 1-2 Effect of herd immunity on spread of infection When diphtheria was a more common disease, people vaccinated against it were exposed more frequently causing mild reinfection (natural booster effect) Diphtheria eventually became less common, fewer people exposed, fewer subclinical booster infections In Russia, decline in adult immunity levels brought an epidemic recommending adults to secure booster dose 23 24 6  11 Oct 2022 Smallpox Poliomyelitis Worldwide eradication met by immunizing people against the disease Inactivated or killed polio vaccine (IPV) in 1955 – protection to Early attempts at prevention: Buddhist nun grind scabs from patients w/ immunized individual, but no herd immunity Did not produce cell-mediated immunity in the intestine mild forms and blow into the nose of non-immune: variolation Declining rates of paralytic form lulled many, immunization rates Vaccination – from vaca or “cow” noted milkmaids developed less severe for NB decreased  periodic small epidemics form of smallpox Live, attenuated Sabin OPV in 1960s – produced cell-mediated Smallpox vaccine effective against both variola minor (alastrim) and immunity preventing poliovirus replication hence herd immunity  variola major (classical smallpox) eradication in Western world (last known case: Peru in 1991) 25 26 Poliomyelitis Syphilis Gaza strip only used OPV  Cases of paralytic form in Arab children caused by infection w/ bacteria (spirochetes), progresses in stages Of inadequate sanitation, children had other intestinal infections: interfered Primary: highly infectious skin lesion (chancre) filled w/ organism  w/ OPV in the gut Secondary: rash or other lesions (subside spontaneously)  Latent Switching of program to include first injection w/ IPV for blood immunity period  Tertiary: CNS manifestations then OPV as booster for herd immunity Untreated infection  immunity but not absolute, does not protect Only indigenous cases of paralytic form have been iatrogenic by OPV from progressive damage (some herd immunity only) itself: IPV given in infants instead, while OPV reserve for outbreaks Penicillin: chancre immunity did not develop, high-risk individuals repeatedly reacquire and spread the disease 27 28 7  11 Oct 2022 Effects of Sanitation Vector Control and Land Use Patterns 19th century: diarrheal disease – killer of children; TB – for adults Negative side effects from vectors of disease can result from Sanitary Revolution (England) – most important factor reducing infant positive intentions of land use mortality; consequent population growth  Worldwide overpopulation (>7B)  increased pollutants, reduced global fish supply, reduced land for Control of tse-tse fly (vector of African sleeping sickness in cattle cultivation, forest cover and climate change enabled larger numbers of cattle  overgrazing (subject to Demographic gap – reduction in infant mortality  significant difference frequent droughts)  dust bowls (little vegetations)  starvation between birth and death rates: rapid population growth for cattle and humans Iceberg phenomenon - appearance of epidemic paralytic poliomyelitis: most infants are exposed after reduction in maternal passive immunity 29 30 River Dam Construction and Patterns of Disease Synergism of Factors Predisposing to Disease After the dam was erected  incidence of schistosomiasis between diseases or between factors predisposing to disease increased (makes the other worse or easily acquired) STD producing open sores facilitate spread of HIV Before the dams were erected, the sea would move far inland Compromised immunity by AIDS permits reactivation of TB during the dry season and mix w/ fresh river water Malnourished child w/ difficulty making antibodies and repairing tissue River water too salty to support the larvae of the blood flukes or the damage makes it less resistant to infectious disease (e.g. measles infection) mosquitoes Ecological and genetic factors interact to produce new influenza strains Duck and human strains of influenza  infect pigs and mix  new variant 31 32 8  11 Oct 2022 Synergism of Factors Predisposing to Disease Contributions of Epidemiologists Antigenic shift – genetic changes in the virus are major  pandemic Investigating Epidemics and Antigenic drift - genetic changes in the virus are minor  regional New Diseases outbreaks Modes of transmission suggest ways to prevent it Overnutrition and sedentary living – each worsens the impact Lab work-up identify the causal agents and clarify pathogenesis Coexistence of cigarette smoking and pneumoconiosis (coal workers) – lung cancer more likely 33 34 Studying the Biologic Spectrum Surveillance of Community Health Interventions of Disease Field trials – randomized trials of preventive measures, important in Figure 1-3: evaluating vaccine before given to the community Iceberg phenomenon, as needs ongoing surveillance of disease and vaccine side effects illustrated by a diphtheria 1955: Polio surveillance program – outbreak of vaccine-associated epidemic in Alabama. poliomyelitis Slight change from procedure of vaccine production  clumping of poliovirus  some virus not killed by formaldehyde 35 36 9  11 Oct 2022 Surveillance of Community Health Interventions Setting Disease Control Priorities Detection of measles outbreaks from ongoing surveillance Disease control priorities be based on: currently existing size of problem; Unexpected disease in college students who received vaccine before 1 yr w/out follow-up booster (while maternal antibodies are present in their infancy, antigenicity of the vaccine was potential of disease to spread; likelihood to cause death and disability; cost reduced) Recommendation: vaccination at 15 months and booster at 4-6 yrs Larger proportion of national resources was allocated to AIDS than to Terrorist attacks on Sept. 11, 2001: Smallpox response plan (bioterrorism preparation) efforts focused on other diseases affecting similar numbers Surveillance of vaccination vs. smallpox (2000): Vaccine-associated Cardiomyopathy  Rapid increase in incidence for brief period curtailment of a larger-scale program High case fatality ratio during outbreak and before therapy was developed Stockpile of vaccine vs. smallpox emergency Medical and social costs Syndromic surveillance – identify changes in disease occurrence and increases in Ready transmissibility suspicious symptom patterns Known methods of prevention 37 38 Improving Diagnosis, Treatment, and Prognosis of Improving Diagnosis, Treatment, and Prognosis of Clinical Disease Clinical Disease Epidemiologic methods improve clinical medicine: diagnosis, therapy, Determine most effective treatment prognosis  domain of Clinical Epidemiology Use of randomized controlled clinical trial: test hypothesis Diagnosis – identifying the nature and cause of a disease Evaluation of clinical history Understand prognosis or probable course and outcome of a disease Review of symptoms Stratify patients w/ similar disease severity for treatment evaluation Examination Testing Risk estimation Improvement through selection of best diagnostic tests, determination of developed in cardiac risk estimators best cutoff points, strategies to use in screening 39 40 10  11 Oct 2022 Improving Health Services Research Providing Expert Testimony in Courts of Law Used in planning and evaluating medical care Called to testify regarding topics as product hazards, risks and effects Determine present and future community health needs of environmental exposures or medications Claims of damage from general environmental exposure Demographic projection techniques – estimate future size of different age groups Occupational illness claims Medical Liability Analyses of patterns of disease frequency and use of services – estimate Product Liability future service needs Determine effects of medical care in health program evaluation/ cost- Expert medical testimony requires high level of epidemiologic expertise benefit analysis 41 42 Thank you for your kind attention. For questions, e-mail: [email protected] 43 11