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Epidemiology of Infectious Diseases Final
Terms in this set (169)
The study of the DISTRIBUTION and DETERMINANTS of disease frequency in human POPULATIONS
T/F Epidemiology plays a role in public policy, social, and legal arenas
How morbidity or mortality are distributed in a given population (person, place, or time)
Illness, disease, injury
Age, sex, race, social economic status, occupation, education, marital status, health status, immunization status, lifestyle or behavior practices, environmental exposures
T/F Women have a tendency to live longer when they are married rather than single. Whereas, males have the tendency to live longer when they are single.
Women live longer when single.
Men live longer when married.
Geographic areas - Census tracts, neighborhoods, cities, etc.
General locations- Urban, rural, indoors, outdoors, at home, etc.
Time of onset of disease- hour of day, day of week, month
Time of diagnosis of disease
What are infectious diseases classified by?
When 1st symptoms appear
What are chronic diseases classified by?
Time of diagnosis
Brief, unexpected increase in frequency of disease
Commonly manifested in outbreaks
Periodic, often predictable, increases the frequency of a particular M or M
Long term changes in M or M patterns ( May be caused by changes in diagnostic criteria)
Describes the distribution of M or M by person, place, or time variables.
Provides clues to causes of disease and helpful for health planning
Why M or M occurs
Who had a double mastectomy that he mentioned?
Who did terrible things for immunizations/autism?
What state did he mention was very active and therefore has lower rates on diseases states?
Mortality in US in 1900 was mainly caused by what type of diseases?
What were the top 10 diseases that caused mortality in 1900?
1.) Pneumonia 2.) Tuberculosis 3.) Diarrhea and Enteritis
4.) Heart Disease 5.) Chronic Nephritis 6.) Injury
7.) Stroke 8.) Diseases of early infancy 9.) Cancer
Mortality in the US today is mainly caused by what type of diseases?
What are the top 10 diseases that cause mortality in the US currently?
1.) Heart Disease 2.) Cancer
3.) Chronic lower respiratory infection 4.) Stroke
5.) Accidents 6.) Alzheimer's 7.) Diabetes
8.) Kidney Disease 9.) Influenza & Pneumonia
Spike in increase
Constant disease regularly found in a location (Ex: Heart disease in the US)
Epidemic that crosses international borders
*Who is credited as the first epidemiologist?
*What type of explanation for diseases did Hippocrates offer?
Rational rather than supernatural
Who invented the smallpox vaccine?
Who demonstrated that cholera could be transmitted through contaminated water?
Who identified the source of childbed fever and introduced handwashing with chlorinated lime?
Who came up with quality management (analytics) to justify improved hygienic standards at military hospitals?
Who demonstrated that microbes cause disease and vaccinations could be used for disease control?
Who developed strict criteria for establishing bacterial causes of disease?
Who is credited with establishing Germ Theory of disease?
Pasteur and Koch
What study is the most famous heart study in the US and is still being carried out today?
T/F A major goal of epidemiology is to identify subgroups in a population who are at high risk for disease.
True - Helps preventive efforts
Action taken to prevent the development of disease in a person who is well and does NOT have the disease
*What do primary prevention strategies emphasize?
General health promotion and risk factor reduction
Identification of people who HAVE the disease at an early stage through screening and early intervention
*What do secondary prevention strategies focus on?
Focus on early detection and swift treatment of disease, Purpose is to slow, cure, or reduce its impact on individuals or communities.
Both therapeutic and rehabilitative measures once the disease is firmly established
What are the two approaches to prevention?
Population-based and High- Risk
Population based approach
Preventive measure is widely applied to an entire population
What are characteristics of a population based approach?
Inexpensive and non-invasive
High risk group approach
Target a high risk group with a particular disease
What are characteristics of a high risk group approach?
More expensive and is often more invasive and/or inconvenient
Physiological or psychological disfunction
Diseases result from an interaction of a ____, ____, and ____.
Most diseases originate from what?
An interaction of genetic and environmental factors
What is the ecological model?
Explains diseases causation using a paradigm. Disease is caused by an IMBALANCE among host, agent, and environmental factors
What are factors that can cause disease?
Biological, Chemical, Physical, as well as stress, environmental (noise), etc.
Infection persists for years, at times for life
No active multiplication of agent
Body produces antibodies in reaction to an infection or vaccine
Injection of serum
How long does active immunity vs passive immunity take to confer?
Active immunity - 2-3 weeks
Passive Immunity - Immediate
How long does active immunity vs passive immunity last?
Active - Lifetime
Passive - 2 weeks if serum, 6 months if by mom
Resistance of a group to an attack by a disease which a large proportion of members are immune.
(Immunize a large part of the pop. and the rest will be immunized by herd immunity)
What is the most simple statement of disease frequency?
Report the number of people who have a disease or outcome or condition of interest
What units are frequency of disease expressed in?
Per unit size of the population in a specified time period
(Multiples of 10)
The DEVELOPMENT of a disease among those who are free of disease (at risk) over a given time period
*T/F Incidence includes pre-existing cases of disease?
False; Incidence includes only NEW CASES
Snapshot of the proportion who exist with the disease at a point in time
*T/F Prevalence includes pre-existing and new cases of disease?
Proportion of people who are disease free and then become diseased during a specified period of time
CI = Number of new cases developing in a specified period of time / Total population at risk
T/F For CI, everyone is followed for the same time period?
Rate, or velocity at which new cases of disease occur in a population at risk for the disease
Number of new cases developing over the study period/ Total person- time of observation
P= # of persons existing with disease/ # of persons in total population at a point in time
What is prevalence proportional to?
Incidence and average duration
If there is no epidemic or endemic conditions, what is the equation for prevalence?
P = I x avg. D (Incidence x Average Duration)
Prevalence is best for what situations?
Incidence is best for what situations?
Studies of etiology
Why is there a problem in assessing
causality in epidemiologic research?
Requires several factors, data repeatedly reproduced, and there is a latent period between exposure to disease and disease manifestation
That the observed result may be due to
random sampling variability
-Measured by conducting a test of statistical significance
Null hypothesis - nothing is going on, no difference, no association
Alternative hypothesis -Something is happening, there is a difference, there is an association
If p ≤ 0.05
We conclude that chance is an unlikely
explanation for the findings, reject H0, and say that there is a statistically significant association between
the exposure and the disease.
If p > 0.05
We conclude that chance cannot be
excluded as an explanation for the findings, do NOT reject H0, and say there is NO statistically significant association between the exposure and the disease.
What does p value reflect?
Both the strength of the
association and the sample size of the study
Range of values within which the true parameter of interest lies, and gives information both about statistical significance and variability.
May result when the selection of individuals into
the study is influenced differentially by
knowledge of the subject's exposure or
T/F Selection bias can be corrected once it occurs?
May result when there is a lack of comparability
between the accuracy or completeness of information in the study groups.
Differential recall of events between the
May arise from either the investigators
eliciting or interpreting the information differentially
T/F Observation bias can be corrected once it occurs
True - Can introduce features into the study to minimize bias, but cannot adjust for bias in analysis of the study
To prevent interviewer bias, what can be done to the study?
Blind the study
Only participants blinded
Participants and Researcher Blinded
Mixture of effect between the association under study and a third variable.
Confounder is associated with BOTH the exposure under study, and independently of the exposure, be a cause or correlate of the cause of disease
T/F You can control known confounding in the design of the study
Causality is an issue of _______
Factors/Tenents of Causation:
1.) Variable of interest in isolation (Eliminate alternative explanations.
3.) Temporal Arrangement (Exposure before develop disease)
4.) Strength of the Association
5.) Totality of Evidence or Consistency
6.) Biological Credibility
7.) Dose- Response
Answer what question?
Who, What, When, Where?
Correlational/ Ecologic Study
Case Reports / Case Series
Cross- sectional Study
Answer what questions?
Predictive of outcome
Randomize Clinical Trial
Unethical to make someone do something, so you observe the ones that are already doing it
Ethical to give drugs to participants
Correlational or Ecological Studies
Use data from entire populations to compare disease frequencies between different groups during the same period of time, or between the same population at different times
Pros of Correlational/Ecological Studies?
Data in populations, not individuals
Confounding by other variables
Average exposure data, not actual levels
Basic type of descriptive study of individuals
Report- Single patient
Series- Series of patients
Case Report/Series Pros?
Reported in every clinical journal
First alert that something is occurring
No comparison group
Snapshot in time: information on exposure and outcome of individuals assessed simultaneously
Cross-Sectional Studies Pros?
Data available and Regularly updated
No temporal sequence
Descriptive Studies are useful for ______
Formulation of hypotheses
Analytic studies are among individuals with appropriate ______ and _______.
Case control : Initial selection on basis of _______.
Cohort: Initial selection on basis of ______.
Interventional Studies: Exposures are __________.
Allocated by investigators
Con of Prospective Cohort Study?
People lost during follow up
Retrospective Cohort Study
Follows Charts 30 yrs back
Still Starts With Exposure
Type of prospective cohort study in which exposure to drug is allocated by the investigator at the beginning of the study
Case-Control Study Pro's?
Efficient - Time and Money
Examine Effects of Multiple Risk Factors
Unable to have accurate exposure information for the right time period
Cohort Design Pro's?
More Accurate Exposure Information
Look at multiple outcomes
Take longer and More expensive
Need to follow up participants for long periods
Interventional Study Pro's?
Control of exposure
Issues of Compliance
Total Number of Individuals Exposed
Total Number Non-Exposed
Total Number With Disease
Total Number Without Disease
CI exposed =
# Exposed cases/ #Exposed = A/A+B
CI non exposed =
# Non-Exposed Cases / # Non Exposed = C/C+D
T/F You can calculate the Incidence Rates for Case-Control Studies
False, There is No Rate of development of the disease
Say something is 2x, 4x, etc. more
Say something is exactly $2.50 more, etc.
Relative Risk is used for what type of Studies?
Measure of the strength of the association between an exposure and a disease
Cumulative Incidence Ratio
CIe / CIne
Cohort Study with count data ( Have all the data)
Incidence Rate Ratio
Cohort Study with person time data (Lose people during the study)
Risk Ratio =
How to exactly phrase relative risk
Those who are exposed have X times the risk of developing the outcome as those who are non-exposed. (Or, are X times as likely to develop....)
Null Value =
No association: RR = 1.0
Positive Association (Exposure increases risk)
Negative Association (Inverse association: Exposure decreases risk of disease)
Used for Case Control Study
Why Case Control Studies are needed?
To determine the significance of observations in a
group of cases, a comparison or control group is
Design of Case Control Studies
Evaluate exposures relationship with disease:
Group with disease and group without disease (control). Determine proportion of those exposed.
In case control studies, the prevalence of history of exposure should be greater in ______ than ______.
Cases (have disease) than controls (Don't have disease)
Where are case control studies selected from?
Hospitals, clinics, MD practices, community registries
What are problems associated with selecting cases for a case control study?
Selecting from a single hospital - Not generalizable
Selecting only from tertiary hospital - Patients are sicker
Which are preferred in case control studies: Incidence or prevalence cases?
Risk factors related to prevalence may be due to survival rather than development of the disease
Selection of case control controls:
Do not select from a pool that is heavily weighted with a disease not indicative of the general population
-Probability sampling is best because of random sampling aspect
Select, as a control for each case a
resident of a defined area, such as a neighborhood in which the case lives
Random Digit dialing
Terminal four digits of the phone number are randomly selected and the same three digit exchange is used.
people/household, telephones/household, probability of being
home may be related to some exposures, business versus residential numbers,
A case is asked for a best friend who is more likely to participate knowing you
are in the study. This control may be similar in age and other sociodemographic characteristics.
may oversample particular groups, the case identifies the control (i.e.., may elect to choose control based on exposure habits because they are
at low risk)
Hospitals/Clinic control cons?
Sample of an ill-defined reference population that generally cannot be characterized.
Advantages of Case-Control Studies
Efficient in terms of time and money since
the disease has already occurred and a smaller sample size needs to be evaluated.
Efficient way to deal with long latent period
Can examine effects of multiple risk factors
for a single disease
Disadvantages of Case-Control Studies
Potential for bias. Worried about ability to
get accurate exposure information for the
right time period
When is a case-control study warranted?
1st step in determining whether an
exposure is linked to an increased risk of disease
Cohort studies are used to:
Elucidate causal relationshps
Design of a cohort study:
Group of exposed and group of non-exposed. Follow up and compare incidence of disease.
How to choose cohort study participants?
Selecting groups for inclusion in the study on the basis of whether or not they were exposed.
Select a defined population before any of its members become exposed or
before their exposures are identified. One could select a population on the basis of some factor not related to exposure (community residence) and take histories of, or perform blood tests or other assays on, the entire population.
Problem with cohorts?
Study population must be followed for a long period to determine whether the outcome of interest has developed
Exposure and non-exposure are ascertained as they occur
during the study; the groups are then followed up for several years into the future and incidence is measured.
Exposure is ascertained from past records and outcome (development or no development of disease) is ascertained at the time the study is begun.
Advantages of Cohort Studies (5)
Correct temporal sequence
Good for rare exposures
Can study several diseases associated with exposure
If prospective, can minimize bias in exposure
Can measure incidence of disease among exposed
and non-exposed subjects
Disadvantages of Cohort Studies (4)
Generally inefficient for studying rare diseases
If prospective, time consuming
If retrospective, requires already recorded information
Need to minimize loss to follow-up for valid
Selection of cohort non-exposed groups
Exposed and non-exposed should be as similar as possible
with respect to all factors other than the factor under
Sources of Exposure Information
Existing records (medical records)
Direct measurement (genetic studies involving blood and body tissue)
Provided by subjects
What is good f/u?
80% and above
Found within subjects chosen
Have you done f/u well; collected disease, statistically significant?
Is the data generalizable?
When is a cohort study warranted
Cohort study is indicated when good evidence suggests an
association of a disease with a certain exposure (evidence obtained from either clinical observations or case-control or other types of studies).
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