Epi Final Flashcards
Purpose of Analytical Studies?
(2)
- ID & explain the cause of dz
- numerically assess risk factors
3 parts of an Analytical Study?
- Data collection
- Data analysis
- Data interpretation
Study type that compares dz occurrence between “exposed” & “non-exposed”
Cohort study
2 Strengths of Cohort Studies
- Rare exposure
- can examine multiple outcomes of a single exposure
Weaknesses of Cohort Study
(2)
- Not good for rare dz.
- time consuming if there is a long period between exposure & dz.
Prospective Cohort follows groups from _______ to ________.
present to future
Strengths of Prospective Cohorts
(3)
- measure Incidence
- describes temporal relationships
- collect data on possible confounders
Weaknesses of Prospective Cohorts?
(3)
- Expensive & long
- Lack of follow-up can affect validity
- Requires a large # of subjects
Retrospective Cohort follows subjects from _______ to _______.
present to past
Strengths of Retrospective Cohorts
(3)
- data is already present
- cheap
- easy to perform
Weaknesses of Retrospective Cohorts
(2)
- Need good records → confounders
- Selection bias
Relative Risk looks at what?
how many times more/less likely exposed individuals are to get the dz. relative to non-exposed individuals
How do you calculate RR?
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Purpose of Cofidence Interval (CI)?
allows you to determine whether or not the RR/OR can be deemed statistically significant
When is the result said to be statistically significant?
(in regards to the CI)
- if the CI falls entirely on either side of the null value (1.0)
- has be 95% or higher
_______ are study subjects who have the disease of interest in Case-Control Studies.
Cases
What is the purpose of Case-Control Studies?
compare frequency of exposure factors in cases w/ dz and cases w/o dz.
_______ are subjects who are dz free at the time of selection in Case-Control Studies.
Controls
Where does Case Selection come from?
- all cases in a defined population or from the general population
- often more convient
Controls selected from CCS should be __________ to cases in every respect except _______.
- identical
- disease
How do you calculate Odds Ratio (OR)?
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Which study uses OR?
Case-Control Studies
4 Strengths of Case-Control Study?
- Rare dz.
- Multiple exposure
- cheap & fast
- Small # of subjects
4 Weaknesses of Case-Control Studies?
- No Incidence or Prevalence
- Bias→ recall, selection, information, misclassification
- Difficult to establish temporal relationships
- Cofounding
Objective of Randomized Clinical Trials (RCTs)?
subjects followed over time to test possible effects of therapeutic & preventative interventions
Which RCT evaluates whether agent/procedure reduces risk of dz. developing in those currently free from dz?
Field Trial
(Prevention Trial)
3 Strengths of RCTs?
- Control over study situation
- Casual relatioship can be established
- Reduced confounding & bias
5 Weaknesses of RCTs?
- May not accurately represent normal population
- Need large sample size → $$
- May be timely
- Ethical issues
- Bias if no blinding is present
Test that is:
- Applied to animals showing CS of dz.
- Confirms or classifies dz. status
DX tests
This test is used to:
- to ID undiagnosed cases of dz in apparently healthy populations
Screening tests
Sensitivity means?
Probability that a disesed patient will test positive
Specificity means?
Probability that a healthy patient will test negative
What must you use to calculate Sensitivity & Specificity?
Gold Standard Tests
True Positive (TP) means?
a diseased patients that test positive for dz.
True negative (TN) means?
healthy patient that tests negative for dz
False Positive (FP)?
Healthy patient tests POSITIVE
False Negative (FN)?
Sick patient tests NEGATIVE
Calculate Sensitivity!
TP
Dz (+)
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Calculate Specificity!
TN
Dz. (-)
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Calculate Prevalence!
_ Dz (+) _
Total tested
OR
_ (a+c) _
(a+b+c+d)
Calculate Positive Predictive Value (PPV)!
# of diseased subjects that test (+) for dz of interest
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Calculate Negative Predictive Value (NPV)!
Healthy subjects that test (-) for dz of interest
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When is it feasible to implement a Screening Program?
(5)
- Dz. is important to public health
- Test will have a high level of case detection & low level of FPs
- Have facilities available for follow-up & TX
- Test doesn’t harm patient
- cost effective
List the 6 steps of Natural HX of Dz in order!
- biological onset
- preclinical phase
- detectable preclinical phase
- lead time
- critical points
- clincal phase
Phase of Natural HX of DZ where there are no symptoms & may only have sub-cellular changes in DNA?
Biological onset
Phase of Natural HX from biological onset to developement of CS of dz?
Preclinical Phase
The point during preclinical phase before symptoms develop, but dz can be detected using screening tests?
Detectable preclincal phase
Interval by which time of DX is advanced by early screening & early detection methods?
Lead Time
Point(s) in natural HX BEFORE which TX in effective?
Critical Points
List order of the Chain of Infection!
agent → reservoir/host → portal of exit → transmission → portal of entry → susceptible host
T/F: All Amplifier Host = Essesential Hosts
FALSE
T/F: All Essential Hosts= Amplifier Hosts
TRUE!!!
Key Requirement for INFECTION!
host shows IMMUNE RESPONSE
Time period btwn exposure to an agent & onset of CS of dz?
Incubation period
The interval between exposure to an infectious organism and the clinical appearance of disease
Latent Period
Clinically apparent infection = ?
DISEASE
4 possible outcomes of Infection?
- Immunity
- DZ
- Subclincal Infection
- Carrier state
Antigenic Drift is responsible for what 2 things?
- small, gradual mutations
- account for annual epidemics
Antigenic Shift is responsible for what things?
- abrupt, major changes
- new disease states (ex. H1N1)
Calculate Infectivity!
_ infected animals _
exposed animals
Calculate Attack Rate!
(infectivity during an outbreak)
# new cases per period
entire population
Calculate Secondary Attack Rate!
(susceptible animals following known contact w/ 1° case)
_ # of new cases from 1° case _
all those healthy after contact w/ 1° case
Calculate Pathogenicity!
(proportion of infected animals that develop CS)
_ # of infected w/ C.S. _
All infected individuals
Calculate Virulence!
(# of animals that develop severe dz)
_ # w/ severe dz _
All dz. animals
Calculate Case-Fatality Rate!
(proportion of cases that evenutally die from dz)
_ # fatal cases _
All dz animals
Calculate Mortality Rate!
(reflects burden of deaths from dz in the population as a whole)
_ # of deaths from dz _
Total population
What season are respiratory diseases more prevalent?
Winter
What season are food-borne & vector-borne diseases more prevalent?
Summer
CDC definition of Herd Immunity?
accomplished when # of animals w/ acquired immunity is so great that, under natural conditions, a infectious agent can’t enter into or spread w/in a herd.
What happens to Herd Immunity when you introduce susceptible animals to a herd?
(2)
- host resistance is reduced
- Increase in occurrence of infection & dz.
What happens during the Descriptive Phase of an Outbreak Investigation?
- describe dz parameters
- take herd HX
- form case definition
- make epidemic curve
List the 3 components of Case Criteria.
- CS
- immunologic response
- ability to detect agent & confirm it as the cause
List the 4 Phases of Outbreak Investigation.
- Descriptive
- Analytical
- Invervention
- Control
Which 2 biological disasters are FAR more likely to occur?
Natural disasters
Accidental disasters
List the 3 consequences of all Biological Disasters
Health/Economic impact
Psychological impact
Improved Preparedness
Agroterrism definition?
intent to indirectly attack persons by destruction of plant & animal infastructure of a nation
CDC Bioterrorism definition?
deliberate release of viruses, bacT or other agents used to cause illness/death in people, animals or plants
4 Clues to Occurence of Agro/Bioterrorism
- Clustering of dz (normally healthy populations
- Dz outside normal/expected season
- Dissemination over very large areas quickly → if airborne
- Acute morbidity/mortality
These agents belong to what CDC Category?
Ebola
- Y. pestis* (plague)
- B. anthracis* (anthrax)
- C. botulinum* (botulism)
- V. major (*small pox)
- F. tularensis* (tularemia)
- Lassa* virus
Category A
highest priority
What 3 requirements must an agent meet to be considered CDC Category A agent?
- easily transmitted from person to person
- High mortality rate
- requires special action for public health preparedness
What 3 requirements must an agent have to be considered a CDC Category B agent?
- moderately easy to disseminate
- Moderate morbidity & low mortality rates
- requires enchanced DX capacity & DZ surveillance
These agents are all classified under what CDC Category?
- Brucella*
- C. burnetti* (Q fever)
- Salmonella, E. coli, Shigella*
- B. mallei (*Glander’s)
- B. pseudomallei (*Melioidosis)
- C. psittaci* (Psittacosis)
- R. prowazekii* (epidemic typhus fever)
- Alphaviridea* (EEE, WEE, VEE)
- Crytosporidium*
- V. cholerae*
Category B Agents
second highest priority
What 3 requirements are needed to be considered a CDC Category C agent?
- emerging pathogens→ ability to be engineered for mass dissemination
- easy to produce & spread
- potential for high morbidity/mortality rates → major health probs.
List the 2 CDC Category C agents!
Nipah virus
Hanta virus
List the 5 agents in Tier 1 of the Select Agent Program!
HHS & APHIS of USDA
- FMD→ highest priority
- Classical Swine Fever
- Newcastle Dz.
- Vesicular stomatitis
- Avian influenza → highly pathogenic form
What is the lead federal agency in safeguarding America’s livestock & poultry health?
APHIS of the USDA
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