Epidemiology study guide

Define epidemiology

The study of the distribution and determinants of health-related

states in specified populations, and the application of this study to

the control of health problems.

Explain the elements of epidemiology

Distribution- Frequency and pattern. Who, where, when. How much of it is there and how is it spread out?

Determinants - Any factor or characteristic that affects the health or disease susceptibility of a population. Causes and risk factors.

Health-related states Not just infectious disease. Injuries, chronic conditions, behaviors, exposures, health itself.

specified populations - A defined group, not a patient. This is the phrase that separates us from medicine.

Application to control - The point is to do something.

What are the two fundamental assumptions about epidemiology

1.Disease does not occur at random; there are factors which can increase or decrease the likelihood of developing disease.

2.These causal or risk factors, the determinants of disease, can be identified through systematic investigation of populations

What is the difference between descriptive and analytic epidemiology

Descriptive- Counts cases, describes them by person,

place, and time. Produces maps, trend lines, tables of

characteristics, hypothesizes

Analytic- Compares a group with an exposure to a

group without it. Produces measures of association — how

much more disease in one group than the other

What are the W’s of descriptive epidemiology?

What- Disease or health event

When- Time of disease or health event occurrence

Where- lace where disease or health event occurs

Who- persons affected by the disease or health event

What are the W’s of analytic epidemiology

Why- Causes, risk factors, or protective factors for disease or health event occurrence

How- circumstances of disease or health event occurrence or modes of disease transmission

What is a clinical lens

Looking at a health problem from the perspective of an individual patient focusing on diagnosis, treatment and care

What is a population lens

Looking at health problems by focusing on the health of groups or populations rather than one individual

How is prevention accomplished? Give an example

Eliminating exposures or causes, Stopping unhealthy behaviors, Health education, Health policies, laws, regulations, Biosecurity, Sanitation/hygiene, Nutrition, Improving access to health care

What are the 5 core epidemiologic functions & their functions

Field investigation- identification of unreported, ill persons, identification of causes/risks

Analytic studies – Finding the whys and hows, Hypothesis, testing, outbreak, investigations, comparing groups

Evaluating of a public health services

Policy Development

Define exposure

Any factor behavior or event that may influence a person's risk of developing a disease or health outcome

What is a risk factor

any attribute behavior or exposure that is associated with an increased probability of developing a disease or injury

What is a protective factor

Any condition behavior, or characteristic that lowers the chance of disease, injury or poor health in a population

Define population

A group of individuals who share at least one common characteristic or exposure

Define outcome, give examples

A result, disease or health outcome. Examples Our influenza, infection, diabetes, breast, cancer, and autism

Why must exposure come first in time

The causes must proceed the effect in time as this is essential for establishing causation

What was the miasma theory? Why was it important to Snow’s work?

The miasma theory was that everyone in London had become sick due to foul air. This was important to John Snows work because he worked Prove that cholera was actually a water borne disease transmitted through contaminated drinking water

Describe the Broadstreet pump investigation and what Snow did

Snow made a map that marked the deaths on the streets in the cases cluttered around one public pump. He also made exceptions for those who worked in brewery’s Because they drink beer and those In the work house because it had its own well.

What was the issue with Snow’s map? What did it not tell him?

The map shows where the cases were, but it cannot tell you the risk of drinking the water

What was Snow’s experiment that compared the two water companies?

there were two competing water companies in South London with pipes, running down the same street Southwark and Vauxhall Drew, water from the thames downstream of London sewage discharge, well, Landis had moved its intake upstream above the discharge. Snow visited houses recorded Color debts and identified the supplier chemically testing the water when residents did not know

Why is a count not a rate?

Account only tells you how many events occurred while a rate tells you how fast they are happening relative to the size of the population over time

What happens to a comparison when one group is larger than the other?

Comparing the number of cases can be misleading because the larger group may have more cases simply because it has more people

How did Goldberger conclude that Pellagra was not contagious?

Goldberger, his wife, Mary and volunteer colleagues injected and ingested material from pellagra patients to prove the disease was not transmissible None of them developed pellagra

Why did Doll and Hill conduct two studies? How did the two differ?

Doll and hill conducted to studies so they could compare the groups. The first group in 1950 started with those who were already sick the exposure was identified after the outcome occurred And more of the lung cancer patients were heavy smokers. The second group in 1951 started with those who were healthy they asked about 40,000 doctors about their smoking habits then they waited interact who died and of what follow up ran for 50 years

What did the Framingham Heart Study build?

In 1948 heart disease was the leading cause of death in the US and was widely regarded as an inevitable consequence of aging. About 5200 healthy adults, enrolled and examined every two years, which gave the field the term risk factor. Second and third generations are still enrolled

What are the four stages every disease passes through, and what happens in each

Susceptibility – the disease has not yet developed but conditions that favor it are present

Subclinical – Pathological changes have begun. The person feels fine, but would not seek care.

Clinical – signs and symptoms appear. The person notices presents for care may be diagnosed.

Outcome – recovery, disability, or death

At which stage does screening take place? At which stage does clinical medicine begin?

Screening takes place during the Subclinical stage and clinical medicine begins during the clinical stage

What is the infectious disease timeline and what periods are marked on it?

The sequence of events from exposure to an infectious agent through illness and recovery. Infection, subclinical, infection, clinical signs, latent period, Infectious, incubation, clinical

Define the incubation period.

Time in a bowl between exposure to an infectious agent and the appearance of signs or symptoms of the disease

Define the latency period.

Time from exposure to onset of disease applies to non-infectious and chronic disease starts when the exposure occurs ends when the disease develops

Explain the difference between incubation and latency, and which applies to which kind of disease

Incubation is from the time of exposure to an infectious agent until the symptoms appear and is used for acute Infectious diseases latency is the time from infection until the disease becomes clinically apparent and is commonly used for chronic disease diseases

What are the four levels of prevention, and give an example of an intervention at each level

Primordial – Stops the risk factor from ever arising. Example – walkable neighborhoods

Primary - prevents disease before it starts in people who already carry the risk factor. Example – vaccination

Secondary -Detect disease early in the subclinical stage when treatment works better. Example – Mammography

Tertiary – reduced disability complications and reoccurrence in people who already have clinical disease. Example – cardiac rehab.

Which level of prevention reduces incidence?

Primary

Know the epidemiologic triad.

Agent- The biological chemical or physical factor required for disease

Host – the organism that can get the disease or a susceptible

Environment – External conditions that bring the agent and host together

What is the web of causation and how it differs from the triad.

Many factors at multiple levels overtime upstream causes no single caused to remove but many places to intervene. The epidemiological triad focuses on three factors while the web of causation shows how multiple interconnected factors can contribute to a disease

What is the chain of infection and the role of each link.

Infectious agent – the pathogen that causes disease

Reservoir – where the pathogen normally lives and grows

Portal of exit – how the pathogen leads the reservoir

Mode of transmission – how it spreads to another person

Portal of entry how it enters the new host

Susceptible - host a person who can become infected

What does it mean to break the chain, and why is every link an opportunity?

stopping the spread of a disease, but interrupting one of the six lengths to the chain. Every link is an opportunity because if you stop even one link, the infection may not spread to the next person.

What are the modes of transmission and give an example of each.

Vertical – nursing

Horizontal

Direct - kissing

Indirect – Touching a contaminated object

What does descriptive epidemiology do, and why is it the first analytic step?

Organizes the occurrence of health events by person place and time. It decides what counts organizes observations, identifies patterns, and exposes exceptions

Describe the workflow: define, count, divide, compare, hypothesize

Define – what counts as a case

Count - how many event events

Divide – out of what population

Compare – across who where when

Hypothesis – what explains the pattern

Define a case definition and know its four components.

A standard set of criteria used to determine whether a person is considered a Case of a particular disease. Clinical criteria – sign symptoms lab confirmation. Person criteria – age occupation, exposure group, eligibility. Please criteria – jurisdiction, facility, school, event, neighborhood. Time criteria – onset/report date within a defined window

What is a line list and which columns describe person, place, and time.

one row per case and one column per variable. Person = age, vaccination, pregnancy, occupation. Place = home, school, workplace, county, census report. Time = onset date, report date, exposure date

PERSON: know the person variables and what each one stands for

age – the single, most important variable in epidemiology, biology, school, contact patterns, vaccination Schedule, and susceptibility

Sex – biological and social components

Occupation – usually a proxy for an exposure, opportunity, healthcare, childcare, agriculture, travel, animal contact, or public facing work

Income and education – proxies for housing, nutrition, stress, access to care, transportation, insurance, paid leave and information access

Race and ethnicity – exposure to social conditions, discrimination, structural access, measurement practices

PLACE: know the levels at which place can be defined

Nation, state, county, neighborhood, school, worksite, household, event, venue, travel, route or healthcare facility

TIME: know the three time patterns and what each one tells you

Secular trend – is this getting better or worse?

Cyclic/seasonal – went to gather resources went to set up preparedness efforts when to take prevention action when to educate

Epidemic curb – the source of the outbreak

What can time patterns reveal about an outbreak?

Common source exposure, ongoing person to person spread reporting delay, effect of control measures

What are the three things to consider before concluding that cases have truly increased.

Case count increase when population increases

Case counts change when case definition changes

More testing means more cases

What are the four questions used to check the validity of any health statistic.

Who counted? Who was counted? What is the denominator? When?

What is the criteria for evaluating a descriptive data source?

Timelines, validity, representativeness, completeness, comparability

Why does descriptive epidemiology generates hypotheses but cannot test them.

There is not a compare group

Explain why a count alone is usually not enough to compare disease burden.

The same count can be different things in a different population

What are the components of the epidemiologist's basic fraction.

Numerator, denominator, time, multiplier

Define count

Number of events or cases

Define rate

Event occur occurrences in a defined population overtime

Define proportion

Part divided by whole numerator is included in denominator

Define ratio

One quantity divided by another numerator not necessarily part of the denominator

What are the three questions to ask before trusting any disease-frequency number.

What population is being described? What is the event? When is the number measured at a single point in time over a year during an outbreak period or cross person time

Define prevalence

describes the disease burden, or the extent of the presence of a health event at a point in time or during a specific time period

Define cumulative incidence

The proportion of disease free people who develop a disease during a specific time period

Define attack rate

The proportion of people at risk who become ill during a specific outbreak or time period

Define the incidence rate

The rate at which new cases of disease occur occurred in a population of time using person time at risk

Differentiate between prevalence, cumulative incidence, and incidence rate

Prevalence – all existing cases in a population as a specific time

Cumulative of incident – new cases/population at risk

Incident rate – the rate of new cases overtime, using person time at risk

What is the bathtub model and the relationship between prevalence, incidence, and duration.

It shows how prevalence depends on the incidents of disease and how long people have the disease. Water flowing in = incidence. Water in the tub = prevalence. Drain = recovery/death. Water level = Prevalence

Explain how the case fatality rate drives public health action.

Can you say it shows how severe A disease is a higher case fatality rate can lead to public health officials, prioritizing early diagnosis, treatment prevention, and control measures

Why is the infant mortality rate the most commonly used measure for comparing health status among nations?

It reflects the health of the mother and the infant during pregnancy in the year after and it reflects a wide variety of factors

What does a measure of association quantify?

The relationship between exposure and disease among exposed/non-exposed and diseased/non-diseased

Give examples of measures of association

Risk ratio, rate ratio, odds ratio, proportionality mortality ratio

Explain why comparison is the key to every measure of association

Measures of association, determine whether the risk or occurrence of disease differs between two groups by comparing an exposed group with an unexposed group

Define the risk ratio

Risk of outcome in exposed/risk of outcome in unexposed

Define vaccine efficacy

Measures reduction in cases among vaccinated, compared with unvaccinated

Define the odds ratio

Odds of exposure among those with the outcome/odds of exposure among those without the outcome

Why are research studies conducted, for both descriptive and analytic purposes.

Because researchers need to describe what is happening and then investigate why it is happening

What is the taxonomy of epidemiologic studies

A system for organizing epidemiologic studies into different types based on their purpose and design. Descriptive, analytic, observational, experimental

What are the features that characterize different study designs.

What is the unit of observation? How are the study participant selected? Does the researcher passively observe or manipulate the exposure factor? Does the researcher use existing data or obtain new data? What is the Directionality of exposure, how many observations are made of each subject?

What defines an experimental study and an observational study

Experimental – the investigator assigns who is exposed

Observational – the investigator watches an assignment that has already been made