Foundations of Epidemiology Chapter 1 Foundations of Epidemiology

Objectives Define epidemiology Explain the importance of descriptive epidemiology Explain the importance of analytic epidemiology Explain the role of epidemiology in public health practice and individual decision making Define epidemic, endemic, and pandemic Describe common source, propagated, and mixed epidemics Define the concepts and principles of case as used in epidemiology Describe the epidemiology triangle for infectious disease Describe the advanced epidemiology triangle for chronic diseases and behavioral disorders Define the three levels of prevention used in public health and epidemiology Understand basic vocabulary used in epidemiology

Define 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.

Define epidemiology 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

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 Epidemiology involves study of disease states (e.g., cholera, influenza, pneumonia) Epidemiology also involves events injury, drug abuse, and suicide Epidemiology also involves behaviors and conditions associated with health physical activity, nutrition, seat belt use, and provision and use of health services

The importance of descriptive epidemiology Descriptive epidemiology involves characterization of the distribution of health-related states or events by Person - who Place - where Time – when Clinical criteria - what

Descriptive epidemiology Allows us to answer who, what, and where questions This knowledge is prerequisite to effective education, screening, prevention, and control programs Provides policy makers with information that can be used for more effectively allocating scarce health resources. Provides individuals with information that can promote better health.

Analytic epidemiology 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

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 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 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.

Role of 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 leading to informed public health policy and planning, as well as individual health decision making

Public health surveillance Causes of disease Epidemiologic information for influencing public health policy and planning and individual decisions Public health surveillance Causes of disease Completing the clinical picture Program evaluation Efficacy Effectiveness

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

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

Obesity Trends* Among U.S. Adults BRFSS, 1991, 1996, 2003 (*BMI 30, or about 30 lbs overweight for 5’4” person) 1996 1991 2003 No Data <10% 10%–14% 15%–19% 20%–24% ≥25%

Common source, propagated, and mixed epidemics Point Intermittent Continuous Propagated

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 and 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

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 transmission (e.g., Malaria spread through mosquitoes)

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 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.

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 once a disease has been introduced into a population and who became infected from contact with the primary case

Different levels of diagnosis Suspect Probable Confirmed

Different levels of diagnosis 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.

Suspect case An individual or group of individuals who have all of the signs and symptoms of a disease or condition yet has not been diagnosed as having the disease, nor have the cause of the symptoms connected to a suspected pathogen (i.e., any virus, microorganism, or other substance that causes disease)

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 is the cause of the disease Host is an organism, usually a human or an animal, that harbors a disease Environment is 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 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

Reservoir 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 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

Six types of carriers Active carrier Convalescent carrier Healthy carrier Incubatory carrier Intermittent carrier Passive carrier (same as healthy carrier)

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

The chain of infection There is a close association between the triangle of epidemiology and the chain of infection

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.

Three levels of prevention used in public health and epidemiology Primary prevention (occurs prior to exposure) Immunization Sanitation Education Media campaigns Warning labels

Active primary prevention Requires behavior change on part of subject Wearing protective devises Obtaining vaccinations

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

Tertiary prevention 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

Conclusion 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