Chapter 1 - Introduction to Epidemiology

• What is epidemiology?

  • study and analysis of the distribution, patterns, and determinants of health & disease conditions in a defined population

• Descriptive Epidemiology

  • involves characterizations of the distribution of health-related states or events (person, place, time)

• Analytic Epidemiology

  • involves finding & quantifying associations, testing hypotheses, & identifying causes of health-related states or events

• Efficacy

  • ability of a program to produce a desired effect among participants in the program compared to those not in the program

• Effectiveness

  • ability of a program to produce benefits among those who are offered the program

• Epidemics

  • illness or behavior or health-related event in excess of normal

• Endemics

  • ongoing, usual, or constant presence of a disease in a community

• Pandemics

  • epidemic that affects the population of an extensive region

• Common-source

  • specific source

• Propagated

  • infections that are transmitted from one infested person to another

• Case

  • a person in a population who has a disease, disorder, injury, or condition

• Case defined

  • a standard set of criteria

• Primary case

  • first disease case in the population

• Index case

  • first disease brought to the attention of an epidemiologist

• Secondary case

  • person infected after contact with a primary case

• Suspect case

  • individuals or groups who have signs and symptoms but are not diagnosed

• Case severity

  • how disabling or debilitating the illness is (hospital length of stay)

• Epidemiology Triangle

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• Fomite

  • inanimate object that can harbor a pathogen and is capable of being a means of transmission

• Vector

  • invertebrate animal that transmits infection by conveying the pathogen from one host to another

• Reservoir

  • habitat in which the agent normally lives, grows, & multiplies

• Vehicle

  • a fomite intermediary that conveys the infectious agent from its reservoir to a susceptible host

• Carrier

  • contains, spreads, or harbors an infectious organism

• active carrier

  • exposed and harbors the pathogen

• convalescent carrier

  • harbors the pathogen, the recovery phase

• healthy (passive) carrier

  • not all, but exposed and harbors the pathogen

• incubatory carrier

  • exposed and harbors the pathogen, ability to transmit

    • time from infection to illness onset

• intermittent carrier

  • exposed to and harbors, can spread pathogen

    • similar to continuous but it happens at multiple peaks

• Direct

  • un-interrupted and immediate transfer from person to person

• Indirect

  • airborne, vector-borne, and vehicle-borne

• Airborne

  • occurs when droplets or dust carry the pathogen to the host and cause infection

• Vector-borne

  • occurs when an arthropod coveys the infectious agent

• Vehicle-borne

  • involves an inanimate object that conveys an infection from the host

• Chain of Infection

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• Advanced Model Triangle of Epidemiology

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• Levels of Prevention

  • primary, secondary, and tertiary

• Primary prevention

  • preventing diseases or disorders before they happen

• secondary prevention

  • aimed at the health screening and detection activities used to identify disease

• Tertiary prevention

  • limiting any disability by providing rehabilitation when a disease, injury, or disorder has already occurred

Chapter 2 - Historic Developments in Epidemiology

• The First Epidemiologist

  • Hippocrates (460-377 BC)

  • Physicians, with a rational perspective rather than a supernatural take on diseases, introduced terms like epidemic and endemic and observed that different diseases occurred in different locations (malaria and yellow fever)

• Vital Statistics

  • John Graunt (1620-1674)

  • English statistician who used paper records (age, sex, who died, of what, where, and when) aka “Bills of Mortality”, developed and calculated life tables and life expectancy

  • Divided death into 2 types of causes: acute and chronic

• Acute

  • struck suddenly — e.g., cholera

• Chronic

  • lasts’ over a period of time — e.g., emphysema)

• The Disease of Workers

  • Bernardino Ramazinni (1633-1714)

  • professor of medicine who observed disease among workers arose from two causes: the harmful character of materials workers handled and unnatural postures imposed upon the body during work

• Sailors and scurvy

  • James Lind (1716-1794)

  • Scottish naval surgeon observed the effect of time, place, weather, & diet on the spread of disease

  • scurvy occurs after 4-6 wks. at sea, the experimental study was set up with sailors sick with scurvy (12 sailors into 6 groups) — two men were given lemons and oranges, and after 6 days, they were fit for duty, since 1895 The British navy required limes and lime juice to be included in their diet

• Smooth as a Milkmaid’s Skin

  • Benjamin Jesty (mid 1700s) was a farmer and dairyman who noticed that milkmaids never got smallpox, he exposed his wife and kids to cowpox to protect them from smallpox and it worked

  • Edward Jenner (1799-1823) was an English rural physician who also noticed that dairymen and milkmaids got cowpox and not smallpox — inoculated an 8 yo boy, James Phipps with Sarah Nelms fresh cowpox legion and later inoculated the same boy with a fresh smallpox lesion to which no disease developed

• Broad Street Pump

  • John Snow (1813-1858)

  • English physician (father of Epidemiology) who studied cholera by identifying incubation times, length of time from infection until death, modes of transmission of cholera, and disease mitigation

    • Later in career he conducted 2 major investigative studies (1) descriptive epidemiologic investigation in which he compared death rates of cholera to where people got their water (3 water companies)

• Childbed “A Tale of Two Words”

  • Ignaz Semmelweis (1818-1865)

  • Hungarian Physician - Obstetrics “Savior of Mothers” and “Father of Hand Hygiene” discovered the classic “wash your hands” after concluding that childbed fever which plagued maternity hospitals throughout Europe was due to the lack of hand hygiene from medical students who carried infection from dissecting room

• Lady with the Lamp

  • Florence Nightingale (1820-1910) mother of modern nursing

  • War of Crimea called FN to care for soldiers in Constantinople - Scutari Hospital

  • Nightingale School of Nursing (1st School of Nursing) and Notes of Nursing

• Baaaaa

  • Louis Pasteur (1822-1895)

  • French chemist, microbiologist, physician who became confident to take on anthrax

  • unclear why bacteria identified as anthrax caused disease as it was present on dead sheep — discovered that anthrax spores were brought to the surface via earthworms and created a vaccine & proved it worked in an experimental study

• Typhoid Mary

  • Marry Mallon (early 1900s) is an Irish chef

  • typhoid fever causes hemorrhage from the inside

  • George Soper found live typhoid virus in Marry Malloy who had been asymptomatic

Chapter 3 - Practical Disease Concepts in Epidemiology

• Communicable disease

  • infectious diseases that are contagious, or capable of being communicated or transmitted

• Non-communicable disease

  • a disease not transmissible directly from one person to another

• Vertical Transmission

  • from an individual to its offspring through sperm, placenta, milk, or vaginal fluid

• Horizontal Transmission

  • infectious agents from an infected person into a susceptible person

• Characteristics of infectious disease agents

  • viability, communicability, infectivity, pathogenicity, and virulence

• Viability

  • ability of the infectious agent to survive outside the host and to exist or thrive in the environment

• Communicability

  • ability of the infectious disease to be transmitted from one person not the next, or spread into a population

• Infectivity

  • ability of an infectious agent to cause infection; measured as the proportion of persons exposed to an infectious agent who became infected

• Pathogenicity

  • ability of an infectious agent to cause disease after infection; measured as the proportion of persons infected by an agent who then experience clinical disease

• Virulence

  • ability of an infectious agent to cause severe disease; measured as the proportion of persons with the disease who become severely ill

• Stages of Disease

  • 1) Susceptibility 2) Pre-symptomatic Disease 3) Clinical Disease 4) Recovery, Disability, or Death

• How the Human Body Resists Infection

  • General resistance or immunity (active or passive)

• Active Immunity

  • the body produces its antibodies against a specific invading substance called an antigen, which offers permanent immunity

  • naturally or artificially acquired active immunity

• Passive Immunity

  • involves the transfer of antibodies to one person produced by another person, short-lived (wks. to most.) immunity

  • naturally or artificially acquired passive immunity

• Herd immunity

  • the notion that if the herd (population or group) is mostly protected from disease by immunity, the chance that a major epidemic occurs is limited

• Communicable Disease and Prevention and Control

  • prevention and control of infectious and contagious diseases are the foundation of all PH measures

  • how we control communicable diseases: remove, eliminate, or contain the cause or source of infection; disrupt and block the chain of disease transmission; protect the susceptible population against infection and disease

• Environmental Control

  • clean water, safer air, pasteurized milk, safe food, management of solid waste, control of vectors (insects and rodents)

• Host-related Control

  • quarantine applies to persons who become exposed to a contagious disease, may or may not be ill

  • isolation applies to people who are known not to be ill with contagious diseases

• Infection-control and prevention

  • personal hygiene and antibiotic prophylaxis

Chapter 4 - Descriptive Epidemiology

• Describes the extent of a public health problem according to person, place, and time

  • communicate a PH problem with the use of tables and graphs

  • identify who is at greatest risk for health-related events or states

  • understand how descriptive epidemiology can provide clues as the causes of diseases

  • descriptive epidemiology is the notion of public health surveillance

• Types of Descriptive Study Designs

  • Ecologic Study – associations on a population level

  • Case Study/Case Series – description of a problem or situation for an individual or group

  • Cross-sectional – examines associations among health-related states or events and personal characteristics, there is no follow-up period.

• Types of Data

  • Nominal – gender, race, marital status, occupation

  • Ordinal – stage of cancer

  • Discrete – new cases of breast cancer reported in US in a given year, number of sick days taken, number of children a family has. Think “counting”

  • Continuous – height, weight, age, temperature. Think “measurement”

• Person

  • answers the WHO question

  • descriptions often include: age, sex, race or ethnicity, marital and family status, occupation, education

• Age

  • has a strong influence on outcomes and findings in studies, thus needs to be considered; if necessary, controlled for in the analysis

• Population pyramids

  • are used to track and compare changes in the population age distributions over time

• Stationary pyramid

  • a population pyramid typical of countries with average fertility and low mortality, very similar to a constructive pyramid

• Expansive pyramid

  • a population pyramid that is very wide at the base, indicating high birth and death rates

• Constrictive pyramid

  • a population pyramid that comes in at the bottom

  • the population is generally older on average, as the country has a long life expectancy and allows a death rate, but also a low birth rate

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• Gender or Sex

  • sex is biologically founded, while gender is a socially constructed notion

• Place

  • descriptive data by place addresses the WHERE question

  • data often involve comparisons between or among geographic locations, in groups before and after migration, and between twins in different settings

• Time

  • epidemiologic investigations range from hours to years or years to decards

  • short-term disease incubation periods of a. few hours can be as important to the epidemiologist as long-term latency periods for chronic diseases, spanning decards

  • temporal is another term occasionally used to describe time factors, time-related elements, or issues

• Time trends

  • examples: temperature measured at noon each day, number of hospital admissions per day

• Point source epidemic

  • individual exposed to the same source over a limited time period

  • shown by a clustering of cases in time with a sharp increase and trailing decline

• Continuous source epidemic

  • exposure is continuous over time

  • shown by a gradual increase, plateau, and then decrease

• Epidemic curve

  • looks like a spike in the graph during the span of time

• Types of time trends

  • secular, short-term, cydic, seasonal

• Secular

  • represent long-term changes in health-related states or events

• Short-term

  • usually brief, unexpected increases in health-relate events or states

• Cydic

  • represent periodic increases and decreases in the occurrence of health-related states or events

• Seasonal

  • represent periodic increases and decreases in the occurrence, interval, or frequency of disease. Tend to be predictable

• Seasonal time trend

  • represent periodic increases and decreases in the occurrence, interval, or frequency of diseases; tends to be predictable

• Surveillance — two types:

  • medical and public health

• What is public health surveillance?

  • communicable diseases, injuries, birth defects, chronic diseases, and health behaviors

• Why surveillance data?

  • the systematic ongoing collection, analysis, interpretation, and dissemination of health data

  • monitor: to identify sudden changes in occurrence, follow long-term trends and patterns, and identify changes in risk factors

  • as a result, we identify whether: Does a health problem exist? Is the problem getting worse?

• Health programs may be aimed at

  • increasing vaccination levels, reducing smoking, increasing fruit and vegetable consumption, increasing physical activity, decreasing obesity, and increasing screening

• What determines the values of a surveillance program?

  • appropriate actions have been taken to date as a result of information from the surveillance system, information has been used to make decisions and take action, monitored prevalence of outcome variable relates to the level and distribution of services available, information may be used in the future

• Final thoughts on descriptive epidemiology

  • confounding factors are always a threat in descriptive studies, analytic epidemiologic studies are better for minimizing the threat of confounding, and descriptive studies are a good first step in the search for causes of health-related states or events

Chapter 6 General Health and Mortality

• life expectancy: the number of years an individual is likely to live

  • 1,000 will change due to how many are in the region

    

Chapter 11 Chronic Disease Epidemiology

• Noninfectious acute conditions

  • things that happen suddenly; e.g., car accident, injury,

• Noninfectious chronic disease

  • characterized by a latency period of 10 to 20 or more years; e.g., heart disease, cancer (typically), diabetes

• Chronic disease epidemiology involves the study of the distribution and determinants of chronic disease and conditions in the human population and the application of the study for

  • preventing and controlling chronic health problems

• William Farr

  • promoted the idea that some diseases, especially chronic diseases, have a multifactorial etiology (set of causes)

• A risk factor is a variable associated with an increased probability of experiencing an adverse health outcome

• The Environment and Chronic Health Problems:

  • physical

  • chemical

  • biological

  • social factors that influence the health status of these people

• Physical stresses and health

  • temperature, radiation, chemicals, toxins, vehicular issues, climate change, and many more

• Exposure to radiation has three basic pathways

  • Inhalation: breathing radioactive materials into the lungs

  • Ingestion: swallowing radioactive material

  • Direct: external exposure

• Toxicokinetics

  • Absorption: entrance of the substance into the body

  • Distribution: movement of the substance from where it enters the body to other sites in the body such as liver, blood and lymph circulation, kidney, and lungs

  • Biotransformation: transformation produced by the body of the substance into new chemicals

  • Excretion: ejection of the substance or metabolites from the body

• The Social Environment and Health

  • War: mental and physical disabilities

  • Families and household: dietary behaviors

  • Social networks and social supports: foster the ability to deal with and survive chronic health problems

  • Neighborhoods and communities: may include environments that facilitate [physical activity, which in turn reduces the risk of certain chronic conditions

  • Public health policy: may reduce exposure to individuals of risk factors for certain chronic diseases

• Behavior and Chronic Health Problems

  • Many of the diseases and conditions today are influenced by the lifestyles of modern populations

  • career pressures, sedentary lifestyles, high-density population living, poor diet, crime, drugs, gangs, poverty, pollution, fear, stress, and economic struggles

• Smoking and chronic disease

  • Cancer

• Diet and chronic disease

  • huge link between diet and cancer - 35% of all cancer is attributed to diet

  • modifying one’s diet can reduce the risk of some cancers and protect against other types of cancer

  • Osteoporosis: one out of every two women over the age of 50 years will have an osteoporosis-related fracture

• Body weight and chronic disease

  • several health complications associated with excessive weight

    • high blood pressure, stroke, heart disease, diabetes mellitus, osteoarthritis, impaired functioning of the heart and lungs, gallbladder disease, hyperlipidemia, obstructive sleep apnea, injuries, cancer

• Sexual practice and chronic disease

  • being sexually active - as opposed to abstaining from or postponing sexual activity

  • having many sexual partners - either serially or concurrently

  • practicing unprotected sex - which includes the irregular or incorrect use of condoms

  • health consequences: sexually transmitted infection, HIV and AIDS, cervical cancer

• Heredity and chronic health problems

  • 10-20% influence of heredity plays into getting cancer

• Risk factors of breast cancer

  • risk increases with age

  • family history of breast cancer (explains 5-10% of cases) many risk factors such as geography, exposure to radiation, obesity, not breastfeeding, having first child at a late age

  • mammography is the most effective method of screening

  • treatable if detected early

• Selected Prevention Behaviors

  • maintaining a healthy weight, eating no more than two or three servings of red meat per week, taking a multivitamin, eating less than one alcoholic drink, eating five or more servings of fruits and veggies per day, eating more high-fiber foods such as grains, include cruciferous veggies, not smoking, getting sleep, protection from sun, avoid workplace exposures, protect self from sexually transmitted infections, and exercise regularly

• Health Belief Model

  • perceived susceptibility: one’s opinion of chances of getting a condition

  • perceived severity: one’s opinion of how serious a condition and its consequences are

  • perceived benefits: one’s belief in the efficacy of the advised action to reduce risk or seriousness of impact

  • perceived barriers: one’s opinion of the tangible and psychological costs of the advice action

  • cues to action: strategies to activate “readiness”

  • self-efficacy: confidence in one’s ability to take action

• Prevention and Control

  • shift from infectious acute disease to noninfectious chronic diseases in the US, public health prevention and control efforts have also changed emphasis

    • as risk factors for disease are identified and the extent of these risk factors made known through epidemiologic study, the potential for effective prevention and control efforts exists

  • prevention and control of noninfectious diseases and conditions is often much more complicated than that of infectious diseases

  • prevention programs need to be specifically tailored to given societies, cultures, and health determinants

    • provides the greatest potential for minimizing public suffering and healthcare costs

• Priorities in Disease Prevention and Control

  • (1) great impact on life

  • (2) suffering from exposures

  • (3) susceptible populations likely to respond

  • (4) which communities are most likely to respond

  • (5) other diseases to be investigated, overlooked, or not being responded

  • (6) which would yield the greatest improved health states, social impact, and economic benefit

  • (7) priority for an epidemiological investigation