© 2010 Jones and Bartlett Publishers, LLC

Foundations of Epidemiology Chapter 1

© 2010 Jones and Bartlett Publishers, LLC  Epidemiology is the study of the distribution and determinants of health-related states or events in human populations, and the application of this study to prevent and control health problems. Objective: Define epidemiology

© 2010 Jones and Bartlett Publishers, LLC  The word epidemiology is based on the Greek words epi—prefix meaning on, upon, or befall; demos—root meaning the people; and logos—suffix meaning the study  In other words, epidemiology is the study of what befalls the population Defining epidemiology

© 2010 Jones and Bartlett Publishers, LLC  Study - Epidemiology involves sound methods of scientific investigation. Methods rely on careful observation and the use of valid comparison groups to determine whether the observed health events differ from what might be expected Key terms in the definition

© 2010 Jones and Bartlett Publishers, LLC  Distribution Study of frequency and pattern of health events in the population Frequency – number, and number in relation to the population Pattern – the health-related state or event by person, place, and time characteristics Key terms in the definition

© 2010 Jones and Bartlett Publishers, LLC  Determinants Search for causes and other factors of health-related states or events Key terms in the definition

© 2010 Jones and Bartlett Publishers, LLC  Health-related states or events Disease states  cholera, influenza, pneumonia, mental illness) Conditions associated with health  physical activity, nutrition, environmental poisoning, seat belt use, and provision and use of health services Events  injury, drug abuse, and suicide Key terms in the definition

© 2010 Jones and Bartlett Publishers, LLC  Application of this study to prevent and control health problems Key terms in the definition

© 2010 Jones and Bartlett Publishers, LLC  Answering the who, what, when, and where questions is prerequisite to effective education, screening, prevention, and control programs Objective: Define descriptive epidemiology

© 2010 Jones and Bartlett Publishers, LLC  Descriptive epidemiology involves characterization of the distribution of health-related states or events by Person - who Place - where Time – when Clinical criteria - what The importance of descriptive epidemiology

© 2010 Jones and Bartlett Publishers, LLC  Analytic epidemiology involves identifying and quantifying associations, testing hypotheses, and identifying causes of health-related states or events  Explains why and how health-related states or events occur Objective: Define analytic epidemiology

© 2010 Jones and Bartlett Publishers, LLC  Identifying risk factors for disease, injury, and death  Describing the natural history of disease  Identifying individuals and populations at greatest risk for disease  Identifying where the public health problem is greatest  Monitoring diseases and other health- related events over time Objective: Identify some activities performed in epidemiology

© 2010 Jones and Bartlett Publishers, LLC  Evaluating the efficacy and effectiveness of prevention and treatment programs  Providing information useful in health planning and decision making for establishing health programs with appropriate priorities  Assisting in carrying out public health programs  Being a resource person  Communicating public health information Objective: Identify some activities performed in epidemiology

© 2010 Jones and Bartlett Publishers, LLC  Epidemiological findings contribute to preventing and controlling disease, injury, disability, and death  How? By providing information leading to informed public health policy and planning, as well as individual health decision making Objective: Explain the role of epidemiology in public health practice and individual decision making

© 2010 Jones and Bartlett Publishers, LLC  Public health surveillance  Causes of disease  Completing the clinical picture  Program evaluation Efficacy Effectiveness See Table 1.1 of text Epidemiologic information for influencing public health policy and planning and individual decisions

© 2010 Jones and Bartlett Publishers, LLC  Screening/Diagnosis What is the sensitivity/specificity of a test? Is prostate specific antigen a good test for prostate cancer?  Causes Why did this patient suffer a stroke? Is obesity the cause of metabolic syndrome? Questions that need epidemiology

© 2010 Jones and Bartlett Publishers, LLC  Treatment Is this the best treatment for Parkinson's disease? Is my surgery as good as that of everyone else?  Prognosis What are the chances of a recurrent heart attack? How long will this knee joint prosthesis last? Questions that need epidemiology

© 2010 Jones and Bartlett Publishers, LLC  Health promotion and protection Do current school meals harm children's future health? Will the Irish smoking ban in public places work better than the English policy?  Health and disease surveillance Why are there 10 fold international differences in suicide rates? When will the next influenza pandemic occur?  Health inequalities Why should life expectancy be nearly five years lower in unskilled manual workers? Do health services reduce or increase health inequalities? Questions that need epidemiology

© 2010 Jones and Bartlett Publishers, LLC  Epidemic – Health-related state or event in a defined population above the expected over a given period of time  Endemic – Persistent, usual, expected health-related state or event in a defined population over a given period of time  Pandemic – Epidemic affecting a large number of people, many countries, continents, or regions Objective: Define epidemic, endemic, and pandemic

© 2010 Jones and Bartlett Publishers, LLC  Common source Point Intermittent Continuous  Propagated Spread from person-to-person  Mixed epidemics A mixture of common source and mixed Objective: Describe common source, propagated, and mixed epidemics

© 2010 Jones and Bartlett Publishers, LLC  Tend to result in more cases occurring more rapidly and sooner than host-to- host epidemics  Identifying and removing exposure to the common source typically causes the epidemic to rapidly decrease Common source

© 2010 Jones and Bartlett Publishers, LLC  Examples anthrax, traced to milk or meat from infected animals botulism, traced to soil-contaminated food and cholera traced to fecal contamination of food and water Common source

© 2010 Jones and Bartlett Publishers, LLC  Arise from infections being transmitted from one infected person to another  Transmission can be through direct or indirect routes  Host-to-host epidemics rise and fall more slowly than common source epidemics Propagated

© 2010 Jones and Bartlett Publishers, LLC  Examples tuberculosis whooping cough Influenza measles Propagated

© 2010 Jones and Bartlett Publishers, LLC  Occurs when a common source epidemic is followed by person-to-person contact and the disease is spread as a propagated outbreak  Example – Shigellosis occurred among a group of 3000 women attending a music festival. Over the next few weeks, subsequent generations of shigella cases spread by person-to-person transmission from festival attendees. Mixed epidemics

© 2010 Jones and Bartlett Publishers, LLC  Disease transmission usually occurs by direct, person-to-person contact (e.g., STDs) fomite-borne (e.g., Hepatitis A spread by a contaminated eating utensil) vehicle-borne (e.g., HIV/AIDS spread through needle sharing drug users) vector-borne transmission (e.g., Malaria spread through mosquitoes) Disease transmission

© 2010 Jones and Bartlett Publishers, LLC  A standard set of criteria, or case definition, assures that cases are consistently diagnosed, regardless of where or when they were identified and who diagnosed the case Accurate assessment requires a standard case definition

© 2010 Jones and Bartlett Publishers, LLC  A case is a person who has been diagnosed as having a disease, disorder, injury, or condition Objective: Define the concepts and principles of case as used in epidemiology

© 2010 Jones and Bartlett Publishers, LLC  The first disease case in the population is the primary case.  The first disease case brought to the attention of the epidemiologist is the index case.  The index case is not always the primary case. Primary case, index case

© 2010 Jones and Bartlett Publishers, LLC  Those 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 Secondary case

© 2010 Jones and Bartlett Publishers, LLC  Suspect An individual who has all of the signs and symptoms of a disease or condition, yet not diagnosed  Confirmed All criteria met Different levels of diagnosis

© 2010 Jones and Bartlett Publishers, LLC  As more information (such as laboratory results) becomes available to the physician, he or she generally upgrades the diagnosis. When all criteria are met and they meet the case definition, the case is classified as a confirmed case. Different levels of diagnosis

© 2010 Jones and Bartlett Publishers, LLC Objective: Describe the epidemiology triangle for infectious disease

© 2010 Jones and Bartlett Publishers, LLC  Shows the interaction and interdependence of agent, host, environment, and time as used in the investigation of diseases and epidemics. Agent is the cause of the disease Host is an organism, usually a human or an animal, that harbors a disease Environment includes those surroundings and conditions external to the human or animal that cause or allow disease transmission Time accounts for incubation periods, life expectancy of the host or the pathogen, and duration of the course of the illness or condition. Triangle is based on the communicable disease model

© 2010 Jones and Bartlett Publishers, LLC  An epidemic can be stopped when one of the elements of the triangle is interfered with, altered, changed, or removed from existence, so that the disease no longer continues along its mode of transmission and routes of infection Stopping an epidemic

© 2010 Jones and Bartlett Publishers, LLC  Fomites Objects such as clothing, towels, and utensils that may harbor a disease agent and are capable of transmitting it; usually used in the plural Example – transmission of cutaneous anthrax from drums to an individual Some disease transmission concepts

© 2010 Jones and Bartlett Publishers, LLC  An invertebrate animal (e.g., tick, mite, mosquito, bloodsucking fly) capable of transmitting an infectious agent among vertebrates  Can spread an infectious agent from an infected animal or human to other susceptible animals or humans through its waste products, bite, body fluids, or indirectly through food contamination Vector

© 2010 Jones and Bartlett Publishers, LLC  Yersinia pestis (the bacteria that cause plague) is found in animals throughout certain parts of the world, most commonly in rats, but occasionally in other wild animals, such as prairie dogs. Plague transmission from these infected animals generally occurs in one of three ways: Yersinia pestisplague  Bites from infected rodent fleas (85%)  Direct contact with infected tissue or bodily fluids For example, people can become directly infected with plague by handling infected rodents, rabbits, or wild carnivores that prey on these animals when plague bacteria enter through the person's skin.plague bacteria  Inhaling infected droplets. Plague

© 2010 Jones and Bartlett Publishers, LLC  The habitat (living or nonliving) on which an infectious agent lives, grows, and multiplies and is dependent on for its survival in nature  Humans often serve as both reservoir and host Reservoir

© 2010 Jones and Bartlett Publishers, LLC  When an animal transmits a disease to a human  Examples – Rabies, Rocky Mountain spotted fever, shigellosis Zoonosis

© 2010 Jones and Bartlett Publishers, LLC  A carrier contains, spreads, or harbors an infectious organism  Example – Typhoid Mary Carrier

© 2010 Jones and Bartlett Publishers, LLC  Direct transmission – direct physical contact such as touching with contaminated hands, skin-to-skin contact, kissing, or sexual intercourse  Indirect transmission – occurs when pathogens or agents are transferred or carried by some intermediate item, organism, means, or process to a susceptible host, resulting in disease Modes of disease transmission

© 2010 Jones and Bartlett Publishers, LLC  There is a close association between the triangle of epidemiology and the chain of infection The chain of infection

© 2010 Jones and Bartlett Publishers, LLC  Infectious diseases are no longer the leading cause of death in industrialized nations so a more advanced model of the triangle of epidemiology has been proposed that better reflects the behavior, lifestyle, and chronic disease issues found in modern times Other modes of causation

© 2010 Jones and Bartlett Publishers, LLC Objective: Describe the advanced epidemiology triangle for chronic diseases and behavioral disorders

© 2010 Jones and Bartlett Publishers, LLC  Primary prevention (occurs prior to exposure) Immunization Sanitation Education Media campaigns Warning labels Objective: Define the three levels of prevention used in public health and epidemiology

© 2010 Jones and Bartlett Publishers, LLC  Requires behavior change on part of subject Wearing protective devises Health promotion Lifestyle changes Community health education Ensuring healthy conditions at home, school and workplace Active primary prevention

© 2010 Jones and Bartlett Publishers, LLC  Does not require behavior change Vitamin fortified foods Fluoridation of public water supplies Passive primary prevention

© 2010 Jones and Bartlett Publishers, LLC  Occurs to reduce the progress of disease  The disease already exists in the person Cancer screening – cancer already present. The goal is to detect the cancer before clinical symptoms arise in order to improve prognosis and prevent conditions from progressing and from spreading Secondary prevention

© 2010 Jones and Bartlett Publishers, LLC  To reduce the limitation of disability from disease  The disease has already occurred Physical therapy for stoke victims Halfway houses for recovering alcoholics Shelter homes for the developmentally disabled Fitness programs for heart attack patients Tertiary prevention

© 2010 Jones and Bartlett Publishers, LLC  Epidemiology involves application of scientific methods for describing the frequency and pattern of health-related states or events  Epidemiology identifies causes of health- related states or events and modes of transmission  Epidemiology guides public health planning and decision making  Epidemiology assists individuals in making informed health behavior changes Conclusion