Epidemiology Flashcards
Define epidemiology
- Epidemiology is the study of the patterns, causes & effects of health and disease in a defined population
- Epidemiologists study sick & healthy people to determine the crucial difference between those who get disease & those who are spared
When do new emergency epidemics arise?
- Epidemics arise when host, agent & environmental factors are not in balance
- Due to new agent
- Due to change in existing agent (infectivity, pathology, virulence)
- Due to change in number of people who are susceptible in the population
- Due to environmental changes that affect transmission of the agent or growth of the agent
What research did John Snow about disease?
- He saw that cholera was spread through a certain region by water.
- Based on his clinical experience and review of epidemiological characteristics of cholera, Snow formulated a theory of causation and transmission of the disease
What is a hypothesis (specifically observation)?
Observations:
A gastrointestinal disease, therefore causal agent was likely ingested
Diarrhea as most prominent symptom, therefore causal agent likely left the body by this route
If cholera excretions contaminated rivers from which drinking water was taken, then the disease could be widely disseminated
What is a hypothesis: causal hypothesis?
Sewage-contaminated drinking water was a causal agent for the cholera epidemic
–John Snow created this
What are some fundamental EPI assumptions?
- Disease doesn’t occur in a vacuum
- Disease is not randomly distributed throughout a population
- Epidemiology uses systematic approach to study the differences in disease distribution in subgroups
- Allows for study of causal and preventive factors
Define population
the total number of inhabitants of a geographic area or the total number of persons in a particular group
Define sample
a selected subset of a population a sample can be random or nonrandom and representative or non-representative
Define random sample
a sample of persons chosen in such a way that each one has the same (and known) probability of being selected
Define representative sample
a sample whose characteristics correspond to those of the original or reference population
What is a prospective study time?
- Looks forward and examines future events
- Follows a condition, concern or disease into the future
What is a retrospective study time?
- Looks back, examines past events
- Looks for causes of things that have already occurred
What are the two types of EPI studies?
- Descriptive studies
2. Analytic studies
Define descriptive EPI studies
- Usually happen at the beginning of an outbreak or when something unusual is happening. These studies organize & summarize data about:
- Persons affected
- Place
- Time
- Describe the basic features of a disease
- These studies usually happen when a disease is first emerging or re-emerging
- Think about the Zika virus…. What is the most important thing to know?
What are the three parts to a descriptive EPI study?
- Person
- Place
- Time
What is the person aspect to a descriptive EPI study?
- Age, gender, ethnicity
- Genetic predisposition
- Concurrent disease
- Diet, exercise, smoking
- Risk taking behavior
- SES, education, occupation
What is the place aspect to a descriptive EPI study?
Age, gender, ethnicity Genetic predisposition Concurrent disease Diet, exercise, smoking Risk taking behavior SES, education, occupation
What is the time aspect to a descriptive EPI study?
- Calendar Time
- Time since an event
- Physiologic cycles
- Age (time since birth)
- Seasonality
Define analytic EPI
Looking at the relationships of disease
For example: explain why and how a health problem occurs
Describe association between exposure and outcome
Test a hypothesis about the cause of disease by studying how exposures relate to the outcome
On a piece of paper, recreate the triad: analytic epi
Host at top, agent and environment on either side
Define host and give two examples
A living organism that is susceptible to or harbors an infectious agent
Ex: Animals, humans
What is a host factor? Give examples
A host factor is an internal factor that influences a person’s exposure, susceptibility, or response to an agent
Ex: Age, race/ethnicity, sex, or behaviors
Define the environment aspect of the analytic EPI and give examples
External factors that affects an agent and the opportunity for exposure
Ex: Climate, housing, travel, health care settings
Define agents in the analytic EPI
A form of energy whose presence/absence is essential for the occurrence of a disease or other adverse health outcome
Ex: Viruses, bacteria, fungi, parasites
Define observational studies
: Describe the outcomes (disease status) or the exposures
Case-control
Cohort
Cross-sectional
Define experimental studies
test treatments
Randomized controlled trials
Define case control studies
- Take a sample of the population and classify them as either cases (diseased) or controls (healthy)
- Because the outcome (disease status) is known, these studies are used to examine/compare the exposures
What are some advantages of a case control study?
- Efficient for rare outcomes (diseases)
- Efficient for outcomes (diseases) with long induction and latent periods
- Can evaluate multiple exposures
- Less expensive and time consuming than a cohort study
What are some disadvantages of case control study?
- Inefficient for rare exposures
- Limited to examining single outcome
- May have poor information on exposure because retrospective
- Vulnerable to recall bias
- Difficult to infer temporal relationship between exposure and disease
Define cohort studies
- Take a sample of the population and classify them as either exposed or unexposed
- Because the exposure is known, these studies are used to examine/compare the outcome (disease status
What are some advantages of a cohort study?
- Best way to ascertain incidence / natural history of disease
- Can calculate incidence rates
- No temporal ambiguity
- Useful for measuring multiple outcomes from an exposure
- Useful for rare exposures
- No ethical concerns
What are some disadvantages of a cohort study?
They expensive
Define cross-sectional study
- Take a sample of the population…
- Just a sample of the population without classifying them based on outcome (disease status) or exposure status
- Because neither disease status or exposure status is know, they examine/compare the outcomes (disease status) and exposure status at the same time
What are some advantages of having a cross-sectional study?
-Estimation of magnitude, distribution of health problem
Intervention planning
-Planning health services, administering medical care facilities
-Examine trends in disease or risk factors over time
-Hypothesis generation
What are some disadvantages of having a cross-sectional study?
- Limited usefulness for inferring disease etiology
- Temporal ambiguity: Cannot determine temporality of exposure and disease
- Do not provide incidence data
- Cannot study low prevalence diseases
Define randomized control trials (RCTs)
- Gold standard in research
- Control group
- Randomization
- Planned experiment where investigators assign study participants to either an intervention or control group
- Trials are designed to test efficacy of intervention or clinical treatment
- They are often blinded to protect against breaches in ethics
- Blind: the participants don’t know treatment status, researchers know treatment status
- Double blind: neither participants nor researchers know treatment status
- Triple blind: neither participants, researchers, nor analysts/review committees know treatment status
Name some advantages of RCTs
- Investigator controls amount, timing and frequency of exposure
- Randomization reduces prejudices and bias
- Blinding reduces prejudices and bias
- Demonstrate cause- effect relationships
Name some disadvantages of RCTs
- Ethical issues
- Difficult to follow people over time; missing outcomes
- Very expensive
- Limited generalizability
What are the two parts of an EPI fraction?
- Numerator: the number of people to whom something happened (i.e. they got sick, died, etc.)
- Denominator: the population at risk - all the people at risk for the event
Define incidence and how to calculate it
-Rate of development of disease in a population over a certain time period
Can help identify emerging diseases, reemerging diseases, or outbreaks
Number of new cases
——————————————
Total population
Define prevalence and how to calculate it
-Number of existing cases of disease in a population
-Can be expressed as a percentage or number of cases per unit size of population
-Indication of extent of health problem; helps us determine need and allocation of resources
Number of all cases (new + old)
——————————————-
Total population
Define the parts of a diagnostic test
- No test is 100% accurate (both sensitive & specific)
- Sensitivity & specificity are linked
- Increasing the sensitivity of a test often decreases the specificity of a test (and vice versa)
What are the two types of results?
True results and false results
Define the two parts to a true result
-True positive: a test indicates disease when there is disease present
T-rue negative: a test indicates NO disease when there is NO disease present
Define the two parts to a false result
- False positive: a test indicates disease when there is NO disease present
- False negative: test indicates NO disease when there is disease present
Define sensitivity
- The ability of a test to correctly identify those who have the disease
- Sensitive tests are good at finding positive results
- A sensitive test may be too good at finding positive results that it give false positive results
- A test with high sensitivity will have few false negatives
Draw 2x2 table that shows sensitivity with test positive and test negative
you got this
Define specificity
- The ability of a test to correctly identify those who do not have the disease
- Specific tests are good at finding negative results
- A specific test may be too good at finding negative results that it give false negative results
- A test that has high specificity will have few false positives
Look at 2x2 table that focuses on specificity
You is kind. You is smart. You is important.
How do you know if a test has good sensitivity and good specificity?
-The test has good sensitivity and it good at finding positive results
-The test may be a little too good at finding positive results because we have a bunch of false positives
-The test has good specificity and it REALLY good at finding negative results.
The test may be a little too good at finding negative results because we have a bunch of false negatives
What is the problem with false positives?
Creates anxiety, etc. changes standard of living
What is the problem with false negatives?
You are walking around sick and don’t know it! You are infecting people while simultaneously decreasing you r quality of life because you have a disease and don’t know it
Reality check
You can’t have a test that is both 100% specific and 100% sensitive
This means you have to choose one or the other depending on the health condition
YOU MADE IT THROUGH MATH GREAT JOB!!
KEEP UP THE GOOD WORK GIRL OKAY YOU GOT THIS
