Introduction to Epidemiology PDF

Introduction to Epidemiology Luis Pablo Hervé Claude Assistant Professor of Veterinary Public Health and Epidemiology Learning objectives Understand what is epidemiology and its application in veterinary science Understand the importance of epidemiology in veterinary practice Understand and know som...

Introduction to Epidemiology Luis Pablo Hervé Claude Assistant Professor of Veterinary Public Health and Epidemiology Learning objectives Understand what is epidemiology and its application in veterinary science Understand the importance of epidemiology in veterinary practice Understand and know some concepts of epidemiology: study designs, measures of disease frequency, surveillance, compartment model, epidemic, causation Susceptible host Breed, age, sex, genotype Physiology and susceptibility Immune response Infectious disease Pathogen Pathogenicity Dispersal efficiency Survival efficiency Inoculation dose Environment Housing management Population density Sanitation Nutrition Prevention Part 1 Epidemiology in veterinary science Epidemiology Science of study and analysis of - the distribution (who, when and where) - and determinants of health and disease conditions in defined populations Epidemiology Purposes Discover: agent, host and factors that affect health Determine: relative importance of causes of illness, disability, and death Identify: population at risk from specific causes Evaluate: the effectiveness of health programs and services Does epidemiology refer exclusively to the study of infectious diseases in population? Individual approach Diagnosis vets use this approach Treatment Diagnostic process Anamnesis Clinical signs Hypothesis=Differential diagnosis Test (laboratory,…) Epidemiology? Diagnosis Treatment and Prevention Who? Infectious disease When? Where? Susceptible host Breed, age, sex Infectious disease Environment Housing management Population density Nutrition Season Prevention Importance of epidemiology in veterinary practice EasAdhpaaaffoe iii Shastri For each disease or condition, you will learn the epidemiology of it Risk of skin cancer in white cats Hip dysplasia prevalence higher in German Shepherds Spirocerca lupi in southern USA Transmission of ringworm by contact Risk of Lyme disease in hunting dogs Bovine Respiratory Disease with peak in fall Importance of epidemiology in veterinary practice For each disease or condition, you will learn the epidemiology of it Risk of skin cancer in white cats Hip dysplasia prevalence higher in German Shepherds Spirocerca lupi in southern USA Transmission of ringworm by contact Risk of Lyme disease in hunting dogs Bovine Respiratory Disease with peak in fall Epidemiological approach in Public Health and Research Outcome Surveillance What is the problem? Intervention Evaluation What is the cause? Exposure Risk Factor What works? How do you do it? Implementation Prevention susceptible Hostside Control Recent research on epidemiology WHO was focused on non communicable* diseases Smoking Cancer Cardio-vascular diseases Obesity - Emerging diseases - Zoonoses exdiabetes diseases emerging zoonoses *A non communicable disease is a noninfectious health condition that cannot be spread from person to person Part 2 Principles of epidemiology and basic concepts 1- Study designs 2- Measures of disease frequency 3- Surveillance 4- Compartment model of infectious diseases 5- Epidemic and endemic 6- Causation in epidemiology 1 Study design Were groups compared? Analytical compareothers vs. Descriptive notcompare Had the researcher any control on variables? Experimental studycontrolvariables vs. Observational studynotcontrolling How many times were the individuals observed? Cross-sectional atweek onepointintime monthyr vs. Cohort intime Forward or backward timeline? ProspectiveForwardtimeline vs. Retrospective backward Measure of disease frequency: Rates 2 Numerator: the number of animals to whom something happened during a period Denominator: the population at risk during this period Mortality Rate Example: 5 deaths per 100 dog-year Incidence Rate Introduction to Surveillance defin ofsurveillance Ongoing systematic collection, analysis, and interpretation of health data Population 3 Compartment model of infectious diseases 4 disease Susceptible Infected Recovered SIR model 22 Compartment model of infectious diseases 4 Carrier Susceptible Infected Infectious Shedder Diseased Recovered Based on infectiousness Based on Clinical signs Latent Period Infectious Period Dead Incubation Period Symptomatic Period 23 Key periods Based on infectiousness Latent period: Time from infection to infectiousness. The pathogen replicates in the host but is not shed yet Infectious period: The pathogen is shed by the individual Based on clinical signs Incubation period: Time from infection to onset of the disease. The pathogen replicates but no clinical signs are observed Symptomatic period: Observation of clinical signs 4 5 Epidemic and endemic Epidemic Excessive occurrence of a disease in a particular geographical region Epizootic Endemic Disease that is regularly present in a particular geographical region Enzootic Pandemic Epidemic at the worldwide scale Panzootic Causation in Microbiology Four (Koch) postulates Must be found in abundance in all organisms suffering from the disease but should not be found in healthy organisms. Must be isolated from a diseased organism and grown in pure culture The cultured microorganism should cause disease when introduced into a healthy organism. Must be re-isolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent. 6 Causation in Epidemiology Bhadra earningObjective 1. Strength of the association The stronger the association between a risk factor and outcome, the more likely the relationship is to be causal ex smoking cancer 2. Consistency of findings Have the same findings been observed among different populations, in different study designs and different times? 6 Causation in Epidemiology 3. Temporal sequence of association Exposure must precede outcome 4. Biological plausibility Presence of a potential biological ice inmy Ings mechanism lungs attain 5. Experiment Does the removal of the exposure alter the frequency of the outcome? 6 What is important? Purposes of epidemiology and importance of epidemiology in practice Diagnostic process and at which stage epidemiology is more relevant Difference between Prevention and Control Different types of study designs Surveillance definition Compartment model definitions Key points for causation in epidemiology TheSIRModelis acompartmentmodelthatdividesapopulationintothreecompartments.ee Susceptible Infected Recovered in a retrospective measure ofdiseasefrequency thedenominatorrepresentsthepopulationatriskduring a specific period respondtopublic Epidemiologicalsurveillanceinvolvestheongoingsystematiccollectionanalysis interpretationofhealthdatatodetectand healththreats Incubationperiodtimefrominfectiontotheonsetof CLINICALSIGNS Infectiousperiodtimeduringwhichanindividualisinfectious of of s latentperiodtimefrominfectiontoinfectiousness andcantransmitthepathogentoothers Purpose compartmentmodel infectiousdiseases exSIR tounderstandthetransmissiondynamics infectiousdiseasesandtopredictspreadofdisease Componentsofepidemiologicalresearch ey of