Epidemiology Book Notes 1 Chapter 1 Foundations of Epidemiology Public is concerned with threats to the population s health Epidemiology is the study of the distribution and determinants of health related states in human Important subfields of public health epidemiology biostatistics and health services populations and the application of this study to the prevention and control of health problems o Greek translation Epi on upon or befall Demos the people Logos the study of Epidemiology involves sound methods of scientific investigations which involve descriptive and analytic methods that draw on statistical techniques for describing data and evaluation hypotheses biological principles and casual theory o Analytic epidemiology involves finding and quantifying associations testing hypotheses and identifying causes of health related states or events Pattern refers to describing health related states or events by who is experiencing the health related state or event person where the occurrence of the state or event is higher or lowest place and when the state or event occurs most or least time In their professional work the focus of epidemiology may be on the environment social issues mental health infectious disease cancer reproductive health and so on Public health assessment identifies if where and when health problems occur and serves as a guide to public health planning policy making and resource allocation Case is a person who has been diagnosed with a health related state or event o Case definition ensures that cases are consistently diagnosed regardless of where or when they are identified and who diagnosed the case Assessment Cause Clinical picture Evaluate o Efficacy refers to the ability of a program to produce a desired effect among those who participate in the program compared with those who do not o Effectiveness refers to the ability of a program to produce benefits among those who are offered the program Epidemics endemics and pandemics o Epidemic is the occurrence of cases of an illness specific health related behavior or other health related events clearly in excess of normal expectancy in a community or region Outbreak in a localized area o Endemic refers to the ongoing usual or constant presence of a disease in a community or among a group of people a disease is said to be endemic when it continually prevails in a region Influenza follows a seasonal trend o Pandemic is an epidemic affecting or attacking the population of an extensive region county or continent o Common source epidemics result in cases occurring more rapidly during the initial phase than do host to host epidemics o Propagated epidemics arise from infections transmitted from one infected person to another can be transmitted directly or indirectly Epidemiology Book Notes 2 o Vehicle borne transmission disease transmission is usually a result of direct person to person contact or of contact with a fomite or vector Syphillis HIV AIDS STDs o Mixed epidemic occurs when victims of a common source epidemic have person to person contact with others and spread the disease resulting in a propagated outbreak Primary case the first disease case in the population o Index case the first disease case brought to the attention of the epidemiologist o Secondary cases the persons who become infected and ill after a disease has been introduced into a population and who become infected from contact with the primary case o Suspect case is an individual or a group of individuals who has all of the signs and symptoms of a disease or condition yet has been diagnosed as having the disease or has the cause of the symptoms connected to a suspected pathogen any virus bacteria fungus or parasite Agent the cause of the disease o Host is an organism usually a human or an animal that harbors the disease the environment includes those surroundings and conditions external to the human or animal that cause or allow disease transmission o Time accounts for incubation periods life expectancy of the host or the pathogen and duration of the course of the illness or condition o Environmental factors can include biological aspects as well as physical stresses excessive heat cold and noise radiation and vehicular collisions workplace injuries and so on chemicals psychosomatic milieu etc Fomite is an object such as a piece of clothing a door handle or utensil that can harbor an infectious agent and is capable of being a means of transmission o Vector is an invertebrate animal bugs that is capable of transmitting an infectious agent among vertebrates A vector can spread an infectious agent from an infected animal or human to other susceptible animals or humans through its waste products bite or body fluids or indirectly through contamination o Resevoir is the habitat living or nonliving in or on which an infectious agent lives grows and multiples and on which it depends for its survival in nature As organisms reproduce in the resevoir they do so in a manner that allows disease to be transmitted to a susceptible host o Zoonosis is an infectious organism in vertebrate animals rabies anthrax etc that can be transmitted to humans through direct contact a fomite or a vector o Vehicle is a nonliving intermediary such as a fomite food or water that conveys the infectious agent from its reservoir to a susceptible host o Carrier contains spreads or harbors an infectious organism The infected person or animal harboring the disease producing organism often lacks discernible clinical manifestation of the disease nevertheless the person or animal serves as a potential source of infection and disease transmission to other humans or animals o Types of carriers Active carrier individual who has been exposed to and harbors a disease causing organism pathogen and who has done so for some time even though they may have recovered from the disease Convalescent carrier individual who harbors a pathogen and who although in the recovery phase of the course of the disease is still infectious Epidemiology Book Notes 3 Healthy carrier also called passive carriers individual who has been exposed to and harbors a pathogen but has not become ill or shown any of the symptoms of the disease Incubatory carrier individual who has been exposed to and harbors a pathogen is in the beginning stages of the disease is displaying symptoms and has the ability to transmit the disease Intermittent carrier individual who has been exposed to and harbors a pathogen and who can spread the