Foundations of Epidemiology Chapter 1 Foundations of Epidemiology

What Is Health? The absence of illness Six dimensions of health

What Are the Six Dimensions of Health? Physical Ability of the human body to function properly; includes physical fitness and activities of daily living. Social Ability to have satisfying relationships; interaction with social institutions and societal mores. Mental Ability to think clearly, reason objectively, and act properly. Emotional Ability to cope, adjust and adapt; self-efficacy and self-esteem. Spiritual Feeling as if part of a greater spectrum of existence; personal beliefs and choices. Environmental Comprised of external factors (i.e., one’s surroundings such as habitat or occupation) and internal factors (i.e., one’s internal structure such as genetics).

What Is Public Health? Public health is the science and art of promoting health and extending life on the population level. Public health is concerned with threats to health in the population (a group of people sharing one or more characteristics). The mission of public health is to ensure conditions that promote the six dimensions of health in the population as a whole.

What Is the Meaning of Population? Population refers to a collection of individuals that share one or more observable personal or observational characteristic from which data may be collected and evaluated. Social Economic Family (marriage and divorce) Work and labor force Geographic factors

How Does Public Health Relate to Epidemiology? There are many subfields of public health, including epidemiology, biostatistics, and health services. Because of its central role in public health, epidemiology is commonly referred to as the foundation of public health.

What Is Epidemiology? 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.

What Is Epidemiology? The word epidemiology is based on the Greek words: epi – prefix meaning on, upon, or befall demos – root meaning the people logos – suffix meaning the study In other words, epidemiology is the study of what befalls the population.

Key Terms in the Definition 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 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 Determinants Search for causes and other factors of health-related states or events

Key Terms in the Definition 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 Application of this study to prevent and control health problems

Why is epidemiology considered by many to be the foundation of public health? Because of its central role in carrying out the three core public health functions: The assessment and monitoring of the health of communities and populations at risk to identify health problems and priorities. The formulation of public policies designed to solve identified local and national health problems and priorities. To assure that all populations have access to appropriate and cost-effective care, including health promotion and disease prevention services, and evaluation of the effectiveness of that care.

The Epidemiologic Focus Clinical focus vs. epidemiologic focus Clinical focus treats the patient as an individual Epidemiologic focus provides information that helps determine public health action to prevent and control health problems

Epidemiology and the Scientific Method Epidemiology uses the scientific method to describe and analyze health-related states or events.

What Is the Scientific Method? The scientific method involves using appropriate study designs and statistical techniques for investigating an observable occurrence and acquiring new knowledge. The health problem Hypotheses Statistical testing Interpretation Dissemination

Study Designs in Epidemiology Descriptive epidemiology Involves study designs used to answer Who?, What?, When?, and Where? Analytic epidemiology Involves study designs used to answer Why? and How? Later chapters will focus on describing these study designs.

The Importance of Descriptive Epidemiology A means to characterizing the distribution of health-related states or events by Person – who? Place – where? Time – when? Clinical criteria – what?

The Importance of Analytic Epidemiology A means to identifying and quantifying associations, testing hypotheses, and supporting statements about causality Explains why and how health-related states or events occur

Selected Activities Performed in Epidemiology 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 Evaluating the efficacy and effectiveness of prevention and treatment programs Obesity increases a person's risk of illness and death due to diabetes, stroke, coronary artery disease, hypertension, high cholesterol, and kidney and gallbladder disorders. Obesity may increase the risk for some types of cancer. It is also a risk factor for the development of osteoarthritis and sleep apnea.

Selected Activities Performed in Epidemiology 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

Epidemiology in public health practice and individual decision making Epidemiological findings contribute to Preventing and controlling disease, injury, disability, and death How? By providing information that leads to informed public health policy and planning, as well as individual health decision making

Selected Types of Epidemiologic Information Public health assessment Causes of disease Completing the clinical picture Program evaluation Efficacy Effectiveness

Questions That Need Epidemiology Diagnosis Is there such a problem as myalgic encephalitis? 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 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 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 tenfold international differences in suicide rates? When will the next influenza pandemic occur?

Questions That Need Epidemiology Health inequalities Why should life expectancy be nearly five years lower in unskilled manual workers? Do health services reduce or increase health inequalities?

Epidemic, Endemic, and Pandemic 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

Common Source, Propagated, and Mixed Epidemics Point Intermittent Continuous Propagated Spread from person to person Mixed epidemics A mixture of common source and mixed Looks like you stopped half way. 25 is random Propagated- person to person

Common Source 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 Examples Anthrax, traced to milk or meat from infected animals Botulism, traced to soil-contaminated food Cholera traced to fecal contamination of food and water

Propagated 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 Examples Tuberculosis Whooping cough Influenza Measles

Mixed Epidemics 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 3,000 women attending a music festival. Over the next few weeks, subsequent generations of shigella cases spread by person-to-person transmission from festival attendees.

Disease Transmission 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 (e.g., Malaria spread through mosquitoes) A fomite is an inanimate object. A vector is an invertebrate animal. Vehicle-borne transmission is related to fomites.

Accurate Assessment Requires a Standard Case Definition 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

Concepts and Principles of Case as Used in Epidemiology A case is a person who has been diagnosed as having a disease, disorder, injury, or condition

Primary Case, Index Case 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

Secondary Case 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

Different Levels of Diagnosis 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 As more information (e.g., 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.

Epidemiology Triangle for Infectious Disease The interrelatedness of four epidemiological factors often contributed to an outbreak of a disease: (1) the role of the host, (2) an agent or disease-causing organism, (3) the environmental circumstances needed for a disease to thrive, survive, and spread, and (4) time-related issues.

Triangle is based on the communicable disease model Shows the interaction and interdependence of agent, host, environment, and time as used in the investigation of diseases and epidemics. Agent – cause of the disease Host – 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

Stopping an Epidemic 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.

Some Disease Transmission Concepts 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

Vector An invertebrate animal (e.g., tick, mite, mosquito, bloodsucking fly) capable of transmitting an infectious agent among vertebrates Transmission can be mechanical (agent does not undergo physiologic changes within the vector) or biological (agent undergoes a part of its life cycle within the vector before transmission to new host) 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 food contamination

Reservoir The habitat (living or nonliving) on which an infectious agent lives, grows, multiplies, and depends on for its survival in nature Humans, animals, food, feces, decaying organic matter Humans often serve as both reservoir and host Public health officials often attack the reservoir of an agent at the environment leg of the triangle of epidemiology. The chain of infection can be broken by destroying the vector in the environment in which it lives. Airplanes are often used to spray the watery breeding places (environment) of mosquitoes in order to kill this vector of malaria, St. Louis encephalitis, yellow fever, and west nile virus.

Zoonosis When an animal transmits a disease to a human Examples – rabies, Rocky Mountain spotted fever, shigellosis

Carrier A carrier contains, spreads, or harbors an infectious organism Example – Typhoid Mary Five types of carriers

Carrier Active – Individual has been exposed and has been harboring disease-causing pathogen; may or may not be recovered Convalescent – Individual in recovery from disease who is still infectious Healthy – Individual has been exposed and harbors disease-causing pathogen but shows no symptoms

Carrier Incubatory – Individual has been exposed and is harboring disease-causing pathogen in beginning stages of the disease, has symptoms, and is infectious Intermittent – Individual in recovery from disease who is still infectious in different places or time intervals

Modes of Disease Transmission 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

Advanced epidemiology triangle for chronic diseases and behavioral disorders Goes beyond infectious disease to include behavior, lifestyle factors, environmental causes, ecological elements, physical factors, and chronic diseases must be taken into account.

Chain of Infection Disease transmission occurs when pathogen leaves the reservoir (e.g., food, water, feces, animal) through a portal of exit (mucous, membranes, wounds) and is spread by a mode of transmission (direct or indirect). Pathogen then enters the body through a portal of entry (mucous membranes, wounds) and infects susceptible host.

Chain of Infection

Other Models of Causation Rothman’s Causal Pies

Active Primary Prevention Requires behavior change on part of subject Wearing protective devices Health promotion Lifestyle changes Community health education Ensuring healthy conditions at home, school, and workplace

Passive Primary Prevention Does not require behavior change Vitamin-fortified foods Fluoridation of public water supplies

Secondary Prevention 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

Tertiary Prevention To reduce the limitation of disability from disease The disease has already occurred Physical therapy for stroke victims Halfway houses for recovering alcoholics Shelter homes for the developmentally disabled Fitness programs for heart attack patients