Epidemiology Exam 1

define epidemiology

the science, or the collection of methods, used to explain the distribution and determination of health-related outcomes in populations

what are the components of the epidemiology triad?

• sick animal

• agent

• host

• environment

what is the purpose of epidemiology?

• determine the magnitude of disease in populations

• study the natural history and prognosis related to disease

• identify causes and predictors of health outcomes

• evaluate preventive and therapeutic factors

• collect quantitative data as the foundation for public policy

define incubation period

the interval from effective exposure to an infectious agent and the onset of related disease

define induction period

the interval from effective exposure to a non-infectious agent and the onset of related disease

define pre-patent period

the interval from effective exposure to the infectious agent and the detection of the agent in the tissues or secretion of the host

define pathogenicity

the ability of an agent to produce clinical disease

define virulence

the ability of an agent to produce severe disease

define infectivity

the ability of an agent to enter, survive, and multiply in the host

define infectious

the ability to transmit infection (indirectly or directly)

define contagious

the ability to transmit infection through direct contact

define latent infection

persistence of an infectious agent within the host without active replication/ shedding

pre-patent period is a type of

latent infection

define carrier state

persistence of an infectious agent within the host without clinical signs or symptoms with active replication and shedding or with the potential to replicate and shed in the future

define reservoir

the biological niche that supports the infectious agent under natural conditions before “escaping” into the animal or human population of interest

define source

the actual object (substance, animal, person) from which the infection is acquired

define vehicle

an inanimate substance that serves to pass an infectious agent to susceptible individuals

define fomite

inanimate object that is capable of transmitting an infectious agent

define vector

animate object that is capable of spreading infection

cases that occur irregularly without a discernable pattern can be described as

sporadic

cases the occur regularly with a perdictable pattern can be described as

endemic

cases that occur clustered in time and space can be described as

epidemic

define pandemic

an epidemic affecting many countries in the world

what are the important characteristics to include when describing an epidemiological situation?

• animal: what are the characteristics of those affected

• place: where were the individuals when they became affected

• time: when did the individuals become affected

define outbreak

a sudden rise in the incidence of disease but is often used for limited geographical distributions

define cluster

an aggregation of cases in place and time that are believed to be greater than expected

define point source

all animals exposed within a short period of time

define line source

point source but with extended time of exposure

what are the stages of the epidemic curve?

1. endemic level

2. ascending part of the curve

3. plateau

4. descending branch

5. secondary peak

what is the cause of the secondary peak?

introduction of new susceptible animals or secondary transmission

describe a seasonal variation series

• dry vs. wet

• summer vs. winter

describe a cyclical trend series

• longer than a seasonal time period

• ex: lynx and hare populations

describe secular trend series

• linear trend

• long time periods

describe erratic variations

• “white noise”

• remaining variation after modeling other components

1 is pointing to

seasonal variation

2 is pointing to

cyclical trend

3 is pointing to

secular trend

what are the types of data classifications?

• qualitative vs. quantitative

• categorical (discrete) vs. continuous

• nominal/ ordinal/ interval/ ratio

define qualitative data

denotes description or subjective impression

define quantitative data

denotes measurable numerical outcome

define discrete data

gaps between possible values (ex. birth order)

define continuous data

no gaps between possible values (ex. weight)

define nominal data

names, no true order (ex. nationality)

define ordinal data

ordered list, spacing between levels is not definable (ex. social class, prognosis)

define interval data

spacing between levels equal and can be quantified (ex. temperature); equality of differences; however, zero point can be arbitrary

define ratio data

highest level of measurement; equality of differences and ratios; there is a true zero point (ex. height, weight, length) something can be twice as long but (typically) not twice as hot

describe categorical variables (discrete)

• information that can be sorted into categories

• types of categorical variables- nominal and ordinal

describe continuous variables

• always numeric

• can be any number, positive, or negative (could be defined as continuous over a restricted range- weight is always positive)

• there are no gaps between values, but the precision of the measuring instrument is a limiting factor

describe dichotomous data

• categorical variable with only 2 levels

• answer to a yes/ no question

• presence or absence of a particular trait or characteristic

a proportion is defined as

a/ (a + b)

a ratio is defined as

a / b

a rate is defined as

a / (time at risk of becoming a)

define uncertainty

used to describe the potential development of disease in individuals

ratio refers to

population and not the individual

define odds

probability that something will occur : probability that something will not occur

define the normality assessment

a statistical procedure done to assume that the data that is under analysis have arisen from a normal population of values

what are methods to evaluate the normality assumption?

• plotting histograms

• descriptive statistics

• formal test for normality

define statistic

is a random value, and its value will change from sample to sample even though the true population value does not change

define parameter

is the true population value; therefore, a statistic is the same as a parameter estimate

mean, median, and mode should be

equal

skewness and kurtosis should be

zero

define infectiousness

relates to the ability of an animal to transmit the infection to a new susceptible host

factors that drive disease transmission include

• presence and number of infectious individuals

• level of immunity in the population

• probability of adequate contact

define adequate contact

contact that when it occurs between an infectious and a completely susceptible host will cause disease transmission

describe direct contact

• infected and susceptible animal having the ability to physically touch (immediate proximity to one another)

• transmission often by respiratory route (or venereal disease)

describe indirect contact

• contact with a contaminated environment (feed, water)

• vector or fomite transmission

• airborne transmission over greater distances (not close proximity)

mosquitoes and ticks are examples of

biological vectors

biting flies are examples of

mechanical vectors

what are factors that drive disease transmission?

• presence and number of infectious individuals

• level of immunity (resistance) in the population

• probability of adequate contact

define R_⁰

the expected number of secondary cases produced by a single (typical) infection in a completely susceptible population

R_⁰ = 1

endemic disease state

R_⁰ > 1

increase number of cases, epidemic if susceptible population

R_⁰ < 1

disease will not be maintained in the population

to prevent an epidemic, the immune proportion should be

(R_⁰-1)/R_⁰