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157 Cards in this Set

  • Front
  • Back
How would you define epidemiology?
Study of the occurrence of disease in a population, and the factors that influence disease occurrence and distribution
How is population defined?
The totality of individuals of the same kind that share common attributes
True or False. The underlying premise of epidemiology is that disease is random.
False
The process of epidemiology includes what 3 steps in studying health problems?
Detected
Investigated
Analyzed
The uses of epidemiology include the description of disease occurrence in populations and the study of what type of factors that predispose to disease?
Causal factors
The information gathered from epidemiological studies is used to do what?
-Research new methods for the investigation and control of disease
-Manipulate possible causal factors to reduce disease occurrence and productivity loss
Macroepidemiology address issues at which level?
Global ,international levels (pandemics)
Which type of epidemiology addresses national issues?
Microepidemiology
Which branch of epidemiology studies the disease risk with the presence of susceptibility genes?
Molecular epidemiology
Genetic epidemiology focuses on causal factors of what type?
Genetic
The use of technologies such as IFA to detect disease, falls under which branch of epidemiology?
Seroepidemiology
The study of the distribution of disease as measured by incidence and prevalence is what branch of epidemiology?
Descriptive
Analytical epidemiology is the study of what components of disease?
Determinants of disease such as causal factors using relative risk and odds ratios
Evidence based vet med relies on good clinical trial data and clinical knowledge based on what type of data?
Population data
How does the epidemiologist indentify the cause of a disease?
-Finds assoc. between factors & disease
-Infers possible causal factors
-Descriptive data of disease in populations
-From observation to prevention of disease
The usual (constant) frequency of disease in a population is the definition of what?
Endemic
What is the definition of epidemic?
Occurrence of disease in excess of expected level
What is another term for edemic?
For epidemic?
Edemic- enzootic
Epidemic- epizootic
What type of widespread epidemic involves more than 1 country?
Pandemic
How do you define sporadic disease?
Irregular, haphazard occurrences
The onset of disease my be reported..
-in time
-by time series analysis and what other 2 ways?
-By host related distribution
-By space
Endemic disease occurs at what frequency?
-Expected, usually low and predictable
How are epidemic disease occurrences shown graphically?
Epidemic curves
Name the 3 types of epidemic curves
-Point source
-Continuous, common source
-Propagating epidemic
The point source curve represents what type of epidemic?
Large number of cases in a short period of time
An epidemic in which exposure to the source is prolonged over an extended period of time results in what type of curve?
Continuous common source epidemic
What is a propagating epidemic?
When a case of a disease serves as the source of infection for subsequent cases.
Disease that occurs in a small number of cases over a short period of time is usually called what?
Sporadic disease
A time series analysis of disease serves what purpose?
Identify periods of high or low risk so that causal associations can be explored. Detects temporal trends of a disease.
A secular time series analysis show disease incidence occurring over a long or a short time period?
Long time period
Changes in disease incidence rates over periods of less than 1 year are called what time of time series analysis trend?
Seasonal
The rise and fall of disease occurrence over a period of greater than 1 year is called what type of trend?
Cyclical
Irregular trends reflect what type of occurrence variation in populations?
Random
Host distribution means that disease occurrence is categorized by what?
Host factors such as age, sex, breed
What is the definition of incidence?
Number of new cases occurring in a population over a defined time period
How is incidence usually expressed?
As number per unit of population at risk
How are new cases identified?
Often not possible, screen the population for baseline rate, then those without disease are followed for 1 year then re-screened
What is the definition of prevalence?
Number of cases present at any given time
How is prevalence usually expressed?
As a proportion between 0 and 1 or as a % or as a number per unit of population
What is point prevalence?
Prevalence at a point in time
What is period prevalence?
Number of people that have had the diesease during a certain period of time i.e. a calendar year
Does period prevalence take into account the duration of the disease?
No
In a steady state situation, what is the relationship between prevalence and incidence?
Prevalence = Incidence X Duration
A change in prevalence can be due to what?
-A change in incidence rate
-Change in duration of the disease
-Change in both
Knowing the prevalence of a disease can help with what?
-Interest in existing cases of disease
-Identify major disease problems
-Identifying/evaluating control strategies (vaccinations, de-worming)
Knowing the incidence of disease can do what?
-Predict population's health status
-Assess the probability that an animal within a population may develop a disease of interest
What is meant by the term Attack Rate?
Measure of the proportion of the population that develops disease among the total exposed at the start of an outbreak
What is involved in the process of data visualization?
Plotting data on a map to look for meaningful patterns
What is meant by cluster analysis of spatial distribution?
Measure of disease occurrance in time and space
What is data modeling used for?
Used to test hypotheses and plan health policies
Who developed the concepts of identifying cause-effect relationships?
Evans
Causal factors are grouped into what 3 categories?
-Disease agents
-Environmental influence
-Host factors
What are some disease agents?
Bacterium, virus, non-living causes (temp)
What is meant by the term infection?
The ability of an agent to establish itself in a host
The ability of an agent to produce disease in a range of hosts is the definition of what term?
Pathogenic
What is virulence?
A measure of the severity of disease caused by the agent
What is indicated by a non-statistical association between a cause and a disease?
Arises by chance
What is meant by a statistical association?
Variables (disease and possible cause) are statistically more (or less) frequently associated than due to chance
A statistical association is significant only if a statitistical test shows what type of significance?
95% to 99% probability that the association is not due to chance.
Risk factors can cause disease or....
Increase the likelihood of developing a disease.
In terms of causal factors, a dose of a virus required to cause a disease is considered to be necessary and...
Sufficient
When multiple factors are needed to cause a disease, each factor is said to be what?
Necessary but not sufficient
A dose-response relationship between a cause and a disease shows what association?
Varying amounts of the suspected cause are related to varying amounts of effect
The mechanisms of a disease have what type of basis?
Biological
Which type of study design is the strongest n terms of showing evidence for a causal relationship?
Clinical trial
What 2 measurements measure the strength of the association between cause and effect?
Relative risk
Odd's ratio
What factors can impair making a causal inference?
-Lengthy time interval between cause and effect
-Multiple causes leading to same effect
-Causal factor requires other factors for effect
What is selection bias?
Any error that arises in the selection of the study population
What is surveillance bias?
Assessment of disease my be better in the monitored population
When people/animals are grouped incorrectly, this is called what type of bias?
Misclassification bias
A misclassification of the disease is called what?
Differential misclassification
Putting diseased animals into a control group is what type of misclassification?
Non-differential misclassification
The way in which information is extracted from medical records could be subject to what type of bias?
Information bias
Bias must be eliminated at which stage of a study?
At the commencement
How is bias controlled?
Through careful study design, and careful choice of population, methods of data collection
What is confounding?
Distortion or masking of an association between an exposure and an outcome (disease) because of a third factor
The confounding factor must be associated with the exposure (risk) factor, and be what with the risk factor for the disease?
Independent
What 3 design controls can help minimize confounding?
-Radomization
-Matching
-Restriction
During the analysis of a study, confounding can be minimized by what 2 approaches?
-Stratification - evaluate association within subgroups
-Multivariate analysis - takes into account many variables at one time
Descriptive studies describe patterns of disease according to what 3 components?
-Where
-Who
-When
What are the benefits to descriptive studies?
-inexpensive
-used when little is known about a disease
-less time-consuming
-easy to collect info
Descriptive studies usually lead to what?
A hypothesis that is then tested
The description of a since case or groups of cases is what type of descriptive study?
Case Reports (case series)
What is a big weakness of case reports?
No comparison (control) group
A cross-sectional study is also called what?
Prevalence study
What does a cross-sectional study describe?
a snapshot at any defined point in time
What is a weakness of cross-sectional studies?
-cannot assess cause and effect
-may miss expsoures that vary over time
Cross-sectional data is place into what type of table for analysis?
2 x 2
Descriptive studies that evaluate disease on a group level are called what?
Ecologic or correlational
What is a ecological fallacy?
If an assumption is made that the association found at the herd/group level is also true on the individual level
True or false. Ecological studies can indicate a causal hypothesis, but cannot determine the cause of a disease
True
What is a cohort?
A group of person's sharing particular statistical or demographic characteristics
When is a cohort study usually done?
After a hypothesis is formed from a case control study
A cohort study starts with identifying the exposed cohort and the non-exposed cohort, and then measuring what?
Disease occurrence in each and compare
Prospective cohort studies follow-up disease from where to where?
From present to future
Retrospective cohort studies follow-up disease from where to where?
From past to present
What are the strengths of cohort studies?
-can directly measure incidence
-useful when exposure is rare
-can exam multiple outcomes of a single exposure
-can describe temporal relationships
-can collect data on possible confounders (prospective)
What is a weakness of cohort studies?
Inefficient for rare disease, need to follow large cohort for a long time
What are risk factors?
Any factor associated with an increased risk of becoming diseased or to die
The relative risk (risk ratio, RR) is used to answer what question?
How much more likely are exposed individuals to get the disease relative to non-exposed individuals
How do you interpret an RR close to 1?
Close 1 means that the exposure is probably not associated with risk of disease (greater or smaller than 1, the exposure is associated with disease)
How is the RR calculated?
Incidence in exposed/Incidence in non-exposed (I 1/I 0)
True or false. Knowing the Relative risk (RR) also gives you statistical significance.
False
What value is used to give statistical significance?
Confidence interval
What implication does a 95% confidence level that includes 1, have?
The finding could be due to chance, the result is not statistically significant
A case control study starts with what information?
Disease, as opposed to exposure
In a case control study, control groups are selected from where?
From the defined population
In a case control study, what calculation is used to estimate relative risk?
Odds ratio (AD/BC)
When are case control studies used?
-When a disease is rare
-When there is a long time interval between exposure and outcome
Non-observational, clinical trials are used to evaluate what?
Therapeutic or preventative effects of particular interventions, and etiologic relationships
Groups or subjects, or animals are divided into what 3 groups for a clinical trial?
-A treated control group
-Untreated control group
-Placebo controls
what do therapeutic trials assess?
Test the agent or procedure to dimish symptoms, prevent recurrence or reduced risk of disease or death
What type of trial evaluates whether an agent or procedure reduces the risk of disease in those currently free of disease?
Prevention trials (field trial)
Trial may be of what 3 design types?
-Open
-Blinded
-Double blinded
What are the strengths of clinical trials?
-Researcher has control over the study situation
-Large sample size and design eliminates unwanted factors
-Use of blinding to eliminate bias
-Provides cause-effect data
-Randomization minimizes confounding
What is the use of a screening test?
Indentify individuals that may have a particular disease
For a screening test to be valid, it must be able to do what?
Distinguish those that have the disease from those that don't
In terms of a screening test, what is meant by sensitivity and specificity?
Sensitivity- correctly identifies those that have the disease
Specificity- correctly identifies those that do NOT have the disease
In a screening test, what are false positives.
People who do not have the disease are are erroneously called positive by the test
What is the predictive value of a screening test?
If the test is positive, what is the probability that the animal does HAVE the disease?
How does prevalence affect the predictive value of a screening test?
The higher the prevalence of disease, the higher the predictive value
What factors can affect the reliability (affect the variation) of a screening test?
-Intrasubject variation
-Interobserver variation
What is screening?
The examination of asymptomatic animals in order to classify them as likely/unlikely to have the disease
Why do we screen?
To reduce morbidity and mortality attained by early treatment of cases discovered by screening
When is screening most useful?
When a disease can be detected during its pre-clinical phase
What is the biologic onset of disease?
The point at which there may be a sub-cellular change in the DNA, but no symptoms of disease
What is the term for the time from the onset of disease until clinical signs/symptoms?
Preclinical phase
Signs of disease develop during which phase?
Clinical phase
To evaluate a screening test, what 2 types of study designs are used?
Non-randomized (such as cohort)
Randomized
What is the disease incubation period?
Time between exposure to an agent and onset of clinical signs/symptoms of disease
What is extrinsic incubation period?
Used with vector-borne diseases, time period the agent requires in a vector before it is capable of inducing infection in the next host the vector encounters
What is the term for the period between the intial infection of the host and when the host becomes infectious to others?
Latent period
What is the period of transmission?
Agent is being shed by the host
What factors affect the transmission of a disease?
-agent
-host
-reservoir
-vector
What is a reservoir?
The habitat in which the agent resides and propagates (can be animate or inanimate)
What is an essential or reservoir host?
A host that is required for maintenance and multiplication of the agent
What is the term for the host in which the agent multiplies to high levels, sufficient to spread to other hosts?
Amplifier host
What type of host is not reuqired for maintenance but can become infected with the agent>
Accidental host
What is a dead end host?
A host that cannot spread the infection to other susceptible hosts under natural conditions
What is a mechanical vector?
A vector in which there is no development of the pathogen, the agent is mechanically carried
What type of vector does have replication/development of the pathogen?
Biological vector
name the 3 modes of vertical transmission.
-Tranplacental (in utero)
-Perinatal
-Postpartum
What is the definition of infection?
Encounter of a potentially pathogenic agent with a susceptible human/animal host that shows an immunologic response to infection
What is meant by the carrier state?
The individual sheds the organism but is usually not infected
Description of the occurrence of infectious disease includes what 4 points?
Who
Where
When
What
"Who" includes the host factors, what does "When" include?
Seasonal variation
Secular variation (over prolonged time)
The "What" of disease occurrence describes which aspects of the disease?
Infectivity
Pathogenicity
Virulence
Immunogenicity
What is meant by attack rate?
# of new cases for epidemic period
______________________________

population at risk
What is a secondary attack rate?
Person to person transmission of infection
How is the secondary attack rate usually measured?
In households or schools
What is pathogenicity?
Ability of an agent to induce a disease
What is virulence?
Ability of an agent to induce severe or fatal disease
How is the case fatality rate calculated?
# fatal cases / # total cases
How is the mortality rate calculated?
# of deaths in the population /
# of individuals n the total population
What is immunogenicity?
Ability of an agent to induce an immune response (as measured by antibody production)
What is herd immunity?
Resistance of a group, community or population to the introduction and spread of an infectious disease, based on the collective immunity of the group
How can herd immunity be gained?
Naturally or by vaccination