Download BPH 206 Final Exam: Disease Transmission, Herd Immunity, and Outbreaks and more Exams Advanced Education in PDF only on Docsity!
BPH 206 FINAL EXAM QUESTIONS AND VERIFIED
DETAILED ANSWERS
Disease transmission- ANSWER the process of transferring of a communicable diseasefrom one infected person or host to another
Examples: -obtaining rabies thru dog's bite-obtaining influenza from fellow employee -transmitting syphilis to sexual partner What is herd immunity? - ANSWER Generalized resistance to a specific disease in thepopulation resulting from most people having immunity against the disease
What is low herd immunity? - ANSWER The immune members are more vulnerable to thedisease
Immunity=60% Susceptibility= 40% What is high herd immunity? - ANSWER The immune members are less vulnerable to thedisease
Immunity= 85% Susceptibility= 15%
What is the epi triad model? - ANSWER A model that views three componentsresponsible for the explanation of disease patterns:
Host: a susceptible human or animal that can acquire the disease and providesnourishment for an agent-one that is infected
Agent: Anything that causes disease in this case microorganisms Environment: where the agent and host interface What would be an example of a complex epi triad? - ANSWER You will have your agentthat passes its disease to a vector, such as ticks, fleas, mosquitoes. The vector then goes on to infect a host and an alternate host. What is a basic epi triad? -ANSWER-Host at the top of the triangle, (e.g. susceptiblehuman) -Environment at the bottom right, (e.g. wooded area in back yard)-Agent at the lower left, (e.g. borrelia burgorferi
What is the epi triad and what characteristics of each influences how a disease isspread? -ANSWER-Host characteristics: age, immune status, genetic predisposition
Agent of characteristics: infectivity, pathogenicity (capacity of a microbe to cause adisease), virulence (degree of pathogenicity: severe or not as severe )
Environment: heat, moisture, proximity/interaction of organisms What is the web of causation? - ANSWER schematic of how factors work together tocause disease-particularly used in chronic diseases/noninfectious diseases
- Community, Zoonotic/Vector-borne: Zika, Malaria, H1N1 (swine flu), H5N1 (bird flu) Outbreak Investigation Steps - ANSWER What? - ANSWER 1) Prepare for Field Work: secure official approvals, research thedisease, agree on purpose of the investigation, establish team, roles & responsibilities, and supplies/equipment
- Verify that an Outbreak Exists: is the number of cases at present more than what isexpected?
Compare the number of cases during the time period when outbreak was suspectedwith the number of cases expected during a non-outbreak period
How an outbreak may be identified - notifications from clinicians or laboratorypersonnel; review of regular, passive public health surveillance activities; reports from affected patients and practitioners
- Verify the Diagnosis: Guiding Questions : Are you addressing the problem originally reported? Can you exclude misdiagnosis plus possible laboratory error? Methods: Interviews with affected people, clinical examination of affected people, review ofmedical records and other pertinent clinical, and confirmation of laboratory test results.
Who? Where? When? - ANSWER 4) Define and identify cases: Develop a case definition that minimizes misclassification by distinguishing cases fromnon-cases: a list of criteria utilized in judging whether a person with disease is considered part of the outbreak A) Assures high sensitivity: correctly identifies those with condition TPB) Provides high specificity: rules out people without the condition TN
Sources: public health agency surveillance data, medical system records from hospitals, schooland workplace attendance records, and special surveys
Characterize cases by person, place, time: permits identification of patterns anddevelopment of initial hypotheses regarding potential causes, sources, modes of spread, and comparisons between groups Person: create a line listingPlace: map cases Time: draw an epidemic curve
Formulate hypotheses: a supposition about the source, agent, mode of transmission,or other key feature of an outbreak-speculates how and why the outbreak is occurring
Why? How? Action - ANSWER 7) Test hypotheses:
-Clinical characteristics: symptoms, diagnostic testing, outcomes -Exposures: occupation, diet, drug use, travel history What are plotting maps? - ANSWER Plotting cases on maps allows for the outbreaks tobe characterized based on place. They aid the investigators to narrow in on source and give recommendations to protect others. -Use info from line listing to orient cases in relation to locations: -place of residence, occupation, venues for recreational activity, and activity sites -Spot map, scatter plot, and area map What is the epidemic curve? - ANSWER can be used to characterize the outbreak bytime.
Shows us: -Time period of the outbreak -magnitude of the outbreak-the current status of the outbreak -incubation period or exposure period -outliers -X-axis: time (date of onset)-Y-axis: number of incident cases
What are examples of epidemic curve? - ANSWER Point source: population
Either individual, or a group of people are exposed to a pathogen at a single source at apoint in time, eat food at a wedding and all the guest get sick a few days later, they got sick from the same thing but the time where symptoms showed was different. Common source: environmental hazard that takes place over an extensive period oftime pathogenic agents in a water source Propagated source: infectious agent that spreads from person to person ***graphs on document Attack rate- what is it? - ANSWER measures of cumulative incidence Overall Attack Rate: total number of people in a cohort who developed the disease / totalnumber of persons in the cohort *
Attack rate of exposed group: number of persons exposed and who became ill / totalnumber exposed *
Attack rate of unexposed groups: (# of persons not exposed who developed illness) /(total # of persons not exposed)*
NOTE: look across down the column What is relative risk? - ANSWER Attack rate of exposed/attack rate of unexposed What are elements of case definitions? - ANSWER 1) Clinical/Lab criteria:
What is risk ratio? - ANSWER Provides information on whether an exposure is related toan increased or decreased risk ***Does not take account of absolute level of risk RR= risk in exposed/risk in non-exposed What is risk differences? j (known as attributable risk) - ANSWER the differencebetween two risks and tells us how much of an absolute risk increase occurs due to the exposure **useful for prioritizing public health efforts RD= risk in exposed- risk in non-exposed RD=0, risk is the same in both groups (null) RD>0, risk is higher among exposed RD<0, risk is lower among exposed How might risk difference be used to calculate the number needed to treat? - ANSWERNNT= 1/ risk difference
NNT= the number of patients that must be treated to prevent one outcome fromoccurring **Simple interpretation: # needed to be treated to prevent the disease from occuring What is population attributable risk? - ANSWER considers the impact of an exposurethat is cause of disease in a population
PAR (%) = Total population incidence - incidence in unexposed/ total populationincidence
Interpretation: the proportion of the population's total risk that can be attributed toexposure
Implication: potential for future benefits resulting from eliminating a potentially harmfulexposure
Amount by which the disease could be reduced in a population, if the factor waseliminated
ex: 21.3 % of cases in a population can be attributed to smoking or 21.3% cancer casescan be averted if everyone stopped smoking
How to calculate PAR if incidence in the total population is not known? - ANSWER(incidence in smokers)(% smokers in population) + (Incidence in nonsmokers)(% nonsmokers in population) then you can proceed to use the original formula: (incidence in total population)-(incidence in non-exposed group) How do you calculate attributable fraction among exposed people?-ANSWER (incidencein exposed)-(incidence in unexposed)/(incidence in exposed)
How do you calculate prevented fraction among exposed people?-ANSWER (Incidencein unexposed)-(incidence in exposed)/(incidence in unexposed)
What is validity?-ANSWER the degree to which a test measures what it says itmeasures)(accuracy)
Objective: to get a valid estimate of an effect measure of interest
What is random unsystematic error? - ANSWER Where an error doesn't have anyspecific pattern of occurrence, it is known as random error which is also known as unsystematic error and hence such errors cannot be predicted in advance like anunavoidable error
-Lack of reliability precision Random Error and Prevention - ANSWER Random error cannot be prevented, but it canbe reduced:
-reduced through increasing sample size What are factors that contribute to random error? -ANSWER- Poor precision: occurswhen the factor being measured is not measured sharply
-Sampling error:Arises when obtained values (statistics) differ from the values(parameters) of the parent population
-Variability in measurement How can systematic error (or bias) can be prevented? -ANSWER- If we plan accordinglyand throughout the study process:
-study design -data collection methods-data analysis methods
sample size what is sample size?- ANSWER the number of subjects used in a studyaffects the power of the statistics-abaility to detect an effect
Type 1 and 2 error?- ANSWER Type II error: low sample size which = inability to detectan effect
Type I error: This is when a Null Hypothesis, H0, is rejected incorrectly. It is also calledthe error of the false positive. Type II error: This occurs when a Null Hypothesis which is in fact false is accepted. Type II error is fixed by: Making sure your sample size is going to be large enough toresult in adequate statistical power.
selection bias What is selection bias? Why is it a problem? - ANSWER Systematic errorthat results from the way that subjects are selected into the study and/or because there are selective losses of subjects prior to data analysis Problem: Selection bias leads to a result that is different from what you would have gotten if youhad enrolled the entire target population
Direction of bias: towards the null - ANSWER Positive association is biased TOWARDSthe null value (The null value is a number corresponding to no effect, that is, no association between exposure and the health outcome). True association isunderestimated The direction of bias is towards the null if fewer cases are considered to be exposed orif fewer exposed are considered to have the health outcome.
direction of bias: away from the null - ANSWER Positive association is biased AWAYfrom the null value. True association is overestimated.
Direction of bias is away from the null when either cases are considered as exposedmore often or exposed are considered to have the health outcome more often.
Selection biasStudy design ANSWER Case-control study: controls who are exposed maybe more likely to be selected into the study as compared to controls that are not
Secondary analysis of available data, for instance, medical record Faulty or incompleterecording of data
What is recall bias? - ANSWER the systematic error that arises because of thedifferences in accuracy and completeness regarding memories of past events or experiences. What is interviewer bias? - ANSWER when a person conducting an interview allowedtheir expectations or prejudice to interfere with his or her objective
Social desirability bias what is it? ANSWER Over-reporting of desirable behaviours,underreporting undesirable behaviours differential misclassification ANSWER occurs when either the misclassification ofexposure differes between subjects with and without the health outcome, or the misclassfication of the heath outcome differs between exposed and unexposedsubjects.
Bias to or from the null-small effect Non-differential misclassification-ANSWER A bias that occurs either when themisclassification of disease is nondifferential across all categories of exposure or when the misclassification of exposure is nondifferential across all categories of disease. Bias to null-meangfully different data Sensitivity-ANSWER Sensitivity is the percent of those with disease for which the test ispositive. For sensitivity, consider only those who are true cases. Probability that someone who is truly diseased (or exposed) will be classified correctly. Specificity - ANSWER The probability that someone who is in fact NOT diseased (or NOTexposed) will be correctly classified. the percent of those without the disease for which the test is negative. For Specificity only consider true non-cases.
What is positive predictive value? - ANSWER The probability of having the disease, givena positive test result.
Negative predictive value- ANSWER The probability that an individual who testednegative is actually free of the disease Does the alternative screening test enhance diagnosis? - ANSWER To answer thisquestion compare pre-test probability (prevalence) to post-test probability (predictive value)-look at % improvements. what is counfounding? - ANSWER a distortion (inaccuracy) in the estimated measure ofassociation that occurs when the primary exposure of interest is mixed up with some other factor that is associated with the outcome. Mediation - ANSWER 限定ろく hopeful Uk England Ireland Wales Scotland N. Ireland effect moderation - ANSWER Interaction -
