Unit 1 Flashcards by Danica Wilson

Epi

about or upon

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Demos

populace or people

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Logos

discoursing, writing, or talking about

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Epidemiology

the study of disease in populations, with intention to institute control

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List the 4 aims of epidemiology:

describe, explain, predict, control

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We are not administering a fixed treatment, and we don’t control the exposure factor (temperature). We are not randomizing the animals.

Observational study

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Principle type of epidemiologic study:

observational

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What are the main types of observational studies?

cohort, case-control, and prevalence

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What is action of primary care:

intended to prevent disease

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What is the action of secondary care?

detect disease early with intention to reduce impact

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What is the action of tertiary care?

extend/improve life after diagnosis

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List the steps of the generalized disease pathway?

induction –> incubation period –> signs

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Subjects are randomized to treatment, and receive specific treatments (randomization and control)

true experiments

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Like a true experiment except no randomization (control without randomization)

quasi-experiments

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Neither randomization nor control; subjects self select their treatment

observational studies

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Measures of disease frequency:

rate, risk

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What is the simplest measure of epidemiology?

count of cases

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What type of frequency are we typically interested in?

relative frequency

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Mathematically, what do we commonly use for measuring frequencies?

proportions, ratios, rates

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What are the 2 ways to express incidence?

incidence rate (incidence density)

- cumulative incidence (risk, incidence proportion, attack rate)

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A person can be an incident case only:

once

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Indicates the movement from Well to Diseased:

Incidence

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An expression to describe a change in one quantity with respect to another quantity with the denominator featuring a time component:

rate

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Denominators for rates are in:

person-time/animal-time

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What is the equation for incidence rate?

IR = (# new cases over a pd of time)/ (length of time at risk of developing disease)

When counting animal-time (time at risk), only count time of:

non-diseased animals

Count time for animals until:

- animal gets disease - death from another cause - removed from herd - study terminates - intervention to render it non-susceptible

Proportion of non-disease individuals at the beginning of a period of study that become disease during the period:

simple cumulative incidence

means they can get the condition:

"at risk"

What's the equation for cumulative incidence?

CI = (# of new cases over a period of time)/(number of healthy animals at beginning)

A cumulative incidence rate for an outbreak:

attack rate

When is it appropriate to measure attack rate?

when the exposure occurs in a very short and defined period of time

Attack rate =

(# of new cases)/(number of individuals exposed at the START)

Why is IR used less often than CI?

harder to interpret

IR is applicable to a group, while CI is applicable to:

a group or an individual

What is incidence?

When an animal goes from healthy to sick

How is incidence measured?

- can be measures as a rate with time component in the denominator - risk (fraction from 0-1)

What does incidence represent?

force of disease

Prevalence at a given moment in time, generally the default understanding of prevalence

point prevalence

number of cases identified over a period of time (1 year = annual prevalence):

period prevalence

Prevalence can change based on:

the time that we choose

Why is the other name for "prevalence", a cross sectional study?

measure can be thought of as a "cross section" of a population

Diseases with long duration can have high prevalence if:

they are not fatal

Incidence can change dramatically, but why may prevalence not change?

if disease has long duration

Diseases that have very short durations, or are highly fatal, will have:

prevalence near 0

What does prevalence convey?

the relative need for follow-up care for those affected with a specific disease

Useful when assessing primary control measures:

indicence

Useful to assess the amount of effort needed delivering secondary and tertiary control:

prevalence

Incidence or Prevalence: Which is more useful in evaluating biosecurity/infection control?

incidence

- Have time in the denominator - Apply to a group - Are scientifically precise

rates (incidence density)

- expressed as a proportion - applies to a group or individal - commonly used, may not account for withdrawals

cumulative incidence (risk)

Weighted averages of the strata specific rates and strata specific populations

crude risks (be they death or other)

Important strata to consider in epidemiology:

age, breed, sex, production cycle

List the steps of the infectious disease events:

1. encounter 2. entry 3. spread 4. multiplication 5. damage 6. outcome (restart)

the ease with which a disease agent in spread within a population

communicability

Transmission requires:

a susceptible host, an agent, and the "right" environment to establish an effective contact

Effective contact is:

- contact between infected and susceptible animals | - contact the results in transmission of disease agent

Predicts the number of new cases in the next incubation period interval:

reed frost model

While a predominately conceptual model, is it very helpful with envisioning the primary elements in an infectious disease outbreak as well as a good estimate in endemic diseases:

Reed Frost Model

Cases in the time t+1, where 1 represents an interval of time equal to the incubation period of the agent (reed frost)

C(t+1)

Number of susceptible at time t (reed frost)

the probability of no contact (reed frost)

Cases at time t

Each individual in the reed frost model is in one of three categories:

S, I, R

Average number of secondary cases that develop from one primary case during its entire communicable period in a population of susceptible hosts

R0 (R naught)

R0 =

(# of contacts per unit time) X (probability of transmission per contact) X (duration of infectiousness)

If R0 is > 1:

the infection is maintained

If R0 is < 1:

the infection cannot be maintained

The ability to protect susceptible individuals within a group due to the high proportion of immune individuals in the same population

herd immunity

Reduces the number of susceptible (St) and alters the probability of transmission per contact/effective contact:

resistance

an increased or unexpected occurrence of cases

epidemic

a normal or expected number of cases in time and space

endemic

epidemic over a large area - country or worldwide

pandemic

new cases, force of disease, probability of becoming a case

incidence

cases at a point in time, "commonness" of disease, probability of being a case

Prevalence

Visual display of disease occurrence in time

epidemic curve

What are the two basic types of epidemics:

common source, propagated

Common-Source Epidemic:

results from exposure to a common source (such as contaminated food or water)

Point (or point-source) epidemic:

exposure is sudden and brief (potato salad at a picnic)

Extended Common Source Epidemic:

exposure period is prolonged

The initial slope of the epidemic curve is stepper when the animal density is:

higher

The initial slope of the epidemic curve is steeper when the infectious period is:

longer

What does the slope of the curve suggest?

efficiency of transmission within the population

What's an example of a short term trend?

epidemic

What's an example of a cyclical trend?

- seasonal | - periodic changes in susceptible host population