epidemiology for master degree, Study notes of Epidemiology

Download epidemiology for master degree and more Study notes Epidemiology in PDF only on Docsity! Introduction to Epidemiology : By Tilaye W[MPH/Epid, Asst. Prof.] Aug 2021 Lecture 1 Course outline % Definitions, Concepts and History of Epidemiology % Natural history of disease % Level of disease prevention % Concepts and types of disease causation models 2 Introduction to Epidemiology Aug 2021 Definition of Epidemiology Greek Term: EPI - Upon us DEM | wile LOGOS - Study of 8 if knowledge sf SS Ss 5 Introduction to Epidemiology Aug 2021 Definitions of Epidemiology ~ The study of the frequency, distribution and determinants of disease in human popn (1970). ~The study of the frequency, distribution and determinants of health and health-related states/events in specified populations, and the application of this study to control health problems (1988) [ currently used defn] 6 Introduction to Epidemiology Aug 2021 Key words in the definition are: 1.Frequency=> # of cases in a pop» /quantification of cases/ 2.Distribution=> who? Where? And when? of health and health related events occurrence (Person, Place, Time) 3.Determinants=> event, characteristic or any definable entity that brings about change in health and health related conditions It refers to “why diseases occur in certain places? In a certain period? Or in a certain pop. groups?” Env’tal, socio-economic, genetic, life style, ...... determinants of health 7 Introduction to Epidemiology Aug 2021 Two fundamental assumptions of Epidemiology L.Non-random distribution of diseases: disease occurrence in a pop is not random or by chance There are patterns of occurrence in which some behavioral, environmental and other factors increase the risk of acquiring/developing a particular disease 2. Human disease has causal and protective factors that can be identified through systematic investigation of d/nt pop» 10 Introduction to Epidemiology Aug 2021 Scope of Epidemiology Senetic markers of disease risk: A+ Health related behavior A+ Chronic diseases, injuries, birth defects, Occupatiomat health; Eonlétalchealth communicable diseases van apmAsicable Fee cable diseases 11 Introduction to Epidemiology Aug 2021 History of Epidemiology Hippocrates in the 5th century B.C. expressed that env’tal factors can influence the occurrence of disease John Graunt, 1662, / the first time he quantified deaths and births William Farr, 1839 Established vital statistics system as a source for health information / Introduced use of comparison groups in epidemiology 12 Introduction to Epidemiology Aug 2021 Purpose/use of epidemiology: 1. Deals about Causation 2. Studies the natural history of diseases 3. Description of health status of populations 4. |ldentify determinants of diseases 5. Evaluation of intervention programs /effectiveness, .../ 6. Classification of diseases 15 Introduction to Epidemiology Aug 2021 Natural History of Disease = It refers to the progression of disease process, in the absence of intervention = It begins with exposure to causative agent capable of producing disease " Without intervention, the process ends with recovery, disability or death = Halted at any time in the progression by intervention, host factors, other influences 16 Introduction to Epidemiology Aug 2021 NATURAL Hx... Two gradients/dynamics in Natural Hx of disease 1.Dynamics of infection: stages in this dynamics are susceptible, latent period, infectious period and non infectious (dead, recovered). => Time line for infection is important for the parasite/agent and public healt. 2. Dynamics of disease: stages in this dynamics are susceptible, incubation period, symptomatic period, non diseased (dead, removed, immune, carrier). =>Time line for disease is important to infected person and health worker 17 Introduction to Epidemiology Aug 2021 - Incubation period in infectious diseases, is equivalent to combination of induction and latent periods in non infectious diseases - Induction period is the period of time from causal action until disease initiation - Latent period: The period b/n exposure and onset of infectiousness (this may be Shorter or longer than the incubation period) 20 Introduction to Epidemiology Aug 2021 Stages in natural history ... 3.Stage of pre symptomatic disease or sub clinical stage- there is no manifestations of a disease. 1 In other words no signs and symptoms are detected. 1 The person does not know that s/he has any disease. 1 The sub clinical stage of disease may lead to the clinical stage or the individual may recover. 4. The clinical stage- stage the person has symptoms & signs of disease. 1 There are various grades of illness with d/nt outcomes depending on the agent host interaction. 1 Some diseases are short and mild that every one recovers quickly while others are very serious leading to complications and death. 21 Introduction to Epidemiology Aug 2021 Stages in natural history ... 5. Stage of disability - some diseases run their course and then resolve completely either spontaneously or under the influence of therapy ’ However, there are a number of conditions which give rise to residual defects of short or long term duration leaving the person disabled to a greater or lesser extent 22 Introduction to Epidemiology Aug 2021 Levels of Disease Prevention... 2. Secondary Prevention "is an early detection and Rx of disease, to prevent severe forms of the disease and spread to others - Early detection depends on the clinical stage and availability of investigation facilities - Limit severity and spread of disease, that is decrease secondary cases Objective: is either to stop or to slow the progression of disease so that to prevent or to limit permane damage, through early detection and treatment o disease 25 Introduction to Epidemiology Aug 2021 Levels of Disease Prevention... 3. Tertiary Prevention "It is limiting disability and rehabilitation Objective: is to limit the physical, psychological, social and economical impact of disability | Tertiary prevention activities involve the care of established disease, with attempts made to restore to highest function, minimize the negative effects of disease, and prevent disease-related complications 26 Introduction to Epidemiology Aug 2021 Types of rehabilitation 1.Restore function- e.g. surgical correction of leprosy =>Medical Rehabilitation 2.Vocational training- so that the individual can earn his/her livelihood=>Vocational Rehabilitation 3.Integrate family with society => Social Rehabilitation 4.Instill self confidence => Psychological Rehabilitation 27 Introduction to Epidemiology Aug 2021 Risk Factors "Risk factor- is commonly used to describe factors that are positively associated with the risk of development of a disease but are not sufficient to cause the disease "Some factors are associated with many d/ses while some d/ses are associated with many factors Four types of factors play a part in the causation of disease 1.Predisposing Factors- such as age, sex and previous illness, may create a state of susceptibility to the disease agent - Lay ground for disease occurrence 30 Introduction to Epidemiology Aug 2021° 2.Enabling Factors- like poor income, nutrition, housing & inadequate medical care may favor the dev’t of d/se (realize occurrence of d/se) 3. Precipitating Factors- events which favor exposure to specific d/se agent or noxious agent may associated with the onset of d/se immediate factors that triggers disease occurrence e.g feeling of anger/depression for drug use 4. Reinforcing Factors- such as repeated exposure and unduly hard work may aggravate an established disease or state Strengthen the motivation for a behavior e.g. repeated exposure 31 Introduction to Epidemiology Aug 2021 There are different theories about cause of disease: = Supernatural /curse of God, evil force/ = Hippocratic/punishment inflicted by the gods but rather the product of environmental factors, diet and living habits/ = Single germ/d/se is caused by germ/ = Classic epidemiologic = Ecological " Multifactorial causation 32 Introduction to Epidemiology Aug 2021 Multifactorial Causation Theory- recently accepted theory = Pettenkoffer contradicted the uni-factorial theory of d/se causation and emphasized that d/se occurrence explained by Multifactorial causation = Several causes or factors acting jointly, cumulatively, by complementing or in an unexplained manner will lead to the d/se " This concept of disease causation is accepted recently 35 Introduction to Epidemiology Aug 2021 Models of Disease Causation "Models are purposely simplified representations = Models facilitate the understanding of nature easily, which is complex =" There are different disease causation models, the following are the widely used ones: ' Epidemiologic triangle, | Web of causation, | Wheel model, | Sufficient-component cause model 36 Introduction to Epidemiology Aug 2021 1. The Epidemiologic Triangle " Was widely used for many years and still referred frequently in epidemiological literature = Consists of three components: host, environment and agent = Each component must be analyzed and understood for prediction of patterns of a disease = This model highlights the agent of disease as a separate component Host " Better used in infectious disr” ‘ing " Drawback of this mode") 37 Introduction to Epidemiology Aug 2021 Environment Web of causation ... eee 1 eeee Figure 5.9 2t. 2 @eeee = cece eee %, ¢ 3: Bp £ ° aot | On = ge og = oo +e > oe oo s behaviour animal-human interaction Disease ast le ns Ne net POfo6, @ 2 a — S 4. a 2 %, “ = % = &. = = > 40 Introduction to Epidemiology Aug 2021 3. The Wheel Model * Consists of a hub (the host/human), which has genetic make-up as its core, surrounded by the environment, schematically divided into the three sectors - biological, social, and physical " The relative size of the d/nt components of the wheel depend upon the specific disease problem under consideration Hereditary disease - genetic core is relatively large Measles - state of immunity of the host & biological sector of the environment is large 41 Introduction to Epidemiology Aug 2021 of causation ‘| identifies multiple etiologic factors of Wheel Model disease without emphasizing the agent of disease *Difference with the web of causation I Separately sooo delineates host and Physical env't environmental factors, a distinction useful for Fig. - The wheel model of h@MAtEenoiPainrent interactions analyses 42 Introduction to Epidemiology Aug 2021 Exercise Use models to describe the following health problems: a. Use the Agent-Host-Environment model to describe the role of the human immunodeficiency virus (HIV) in AIDS. | Agent, Host, Environment: b. Some of the risk factors for heart disease are smoking, hypertension, obesity, diabetes, high cholesterol, inactivity, stress, and type A personality. Are these risk factors necessary causes, sufficient causes, or component causes? 45 Introduction to Epidemiology Aug 2021 Chain of Infection > Infection implies the agent has achieved entry and begun to develop or multiply Components of Chain of Infection /6/ » Causative agent >» Reservoir host > Portal of exit >» Mode of transmission > Portal of entry >» Susceptible host. 46 Introduction to Epidemiology Aug 2021 Terms in chain of infection " The reservoir of an agent is the habitat in which an infectious agent normally lives, grows, and multiplies " A carriers is a person without apparent disease who is nonetheless capable of transmitting the agent to others Carriers may be: Asymptomatic carriers: transmitting infection without ever showing symptom Incubatory carriers: transmitting infection by shedding the agent before the onset of clinical manifestations convalescent carriers: transmitting infection after the time of recovery Chronic carriers: shed the agent for a long period of time, or even indefinitely 47 Introduction to Epidemiology Aug 2021 Modes of Transmission of infectious Agents » The mechanism by which the agent escapes from a reservoir host and enter into a susceptible host is referred as mode of transmission. There are two major modes: 1. Direct Transmission - immediate transfer of the agent from a reservoir to a susceptible host by direct contact/droplet spread. >» Touching > Kissing >» Sexual intercourse > Transplacental (vertical) from mother - child 50 Introduction to Epidemiology Aug 2021 Modes of Transmission ... 2. Indirect Transmission- an agent is carried from reservoir to a susceptible host by suspended air particles or by animate (vector-mosquitoes, fleas, ticks ...) or inanimate (vehicle-food, water, biologic products, fomites) intermediaries. ' Vehicle-born: food, water, towels, ... ' Vector-borne: insect animals, ... ' Airborne: dust, droplets ' Parenteral injections 51 Introduction to Epidemiology Aug 2021 > 52 Introduction to Epidemiology Aug 2021