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final content Flashcards

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1
Q

what is an infectious disease

A
  • cases are dependent on exposure to other cases
  • starts with exposure to a pathogen, then infection occurs, then disease MAY occur
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2
Q

infection vs disease

A

infection: established pathogen within the host
disease: the effects of an infection (clinical signs and symptoms)

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3
Q

latent vs incubation period

A

latent period: when host becomes infected to when they become infectious to others
incubation period: from when host becomes infected to when symptoms/clinical signs of disease show

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4
Q

what period is long for asymptomatic hosts

A

incubation period

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5
Q

what is a differential equation

A
  • a function measuring the change in one variable with respect to another
  • a system of differential equations is a set where each equation may or may not be dependent on other variables
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6
Q

a 3-state system for stages of a disease model

A

state 1: suceptible
state 2: infected
state 3: recovered

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7
Q

what does disease transmission depend on

A

the number/proportion of susceptible individuals AND the number/proportion of infectious individuals

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8
Q

generation time vs serial interval

A

generation time = time between infections in 1st and 2nd case
serial interval = time between symptoms of the 1st and second case

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9
Q

how to calculate serial interval

A

serial interval = latent period + (infectious period/2)

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10
Q

reproductive number (R) vs basic reproductive number (R0)

A

R = the average number of secondary infections caused by an initial infectious individual
R0 = the average number of secondary infections caused by an initial infectious individual in a completely susceptible population

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11
Q

basic reproductive number value interpretations

A

R0 > 1: epidemic
R0 = 1: endemic
R0 < 1: fadeout

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12
Q

how to calculate R0 for a SIR model

A

R0 = c x p x d
c = rate of contact
p = probability of transmutation given contact
d = duration of infectiousness

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13
Q

how do you calculate the critical proportion to vaccinate (Pc)

A

Pc = 1- (1/R0)
- as R0 increases more people must become vaccinated

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14
Q

how do you calculate the effective reproductive number

A

Re = R) x proportion susceptible

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15
Q

steps in building and analyzing a disease model

A
  1. define population and pathogen of interest
  2. construct a system of equations
  3. code the model and conduct numerical analysis
  4. assess the effect that interventions have on model outcomes
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16
Q

what interventions can be used to control disease

A
  • vaccination (full immunity)
  • reduce contact
  • reduce probability of infection given contact
  • reduce period of infectiousness
  • increase rate of recovery
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17
Q

why might we use mathematical models for disease control in epidemiology

A
  • ethical concerns for experimental studies
  • no disease present for observational studies
  • expensive and timely
  • to test “what if” scenarios
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18
Q

when would we use an experimental study instead of an observational study

A
  • prophylactic/preventative studies
  • therapeutic studies
  • management strategies
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19
Q

types of experimental studies

A
  1. lab based experiment: researchers create a controllable environment
  2. Randomized control trial: researcher creates groups in a “real-world” setting, no control over environment
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20
Q

pros and cons of lab-based experiments

A

pros: provides best control of manipulative conditions, reduces confounding, can be repeated
cons: lacks external validity, is unrealistic

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21
Q

pros and cons of randomized control trials

A

pros: best form of blinding, answers specific questions
cons: issues with ethics and costs

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22
Q

strongest to weakest strength evidence based research

A

systematic reviews > meta-analyses > blinded RTCs > cohort studies > case-control studies > case series > single case report

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23
Q

how do we conduct RTCs

A

take study population, divide into 2 treatment groups, determine who is O+ and O- from both groups

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24
Q

10 key aspects of conducting RTCs

Study These Flashcards
A
  • clearly defined question
  • is it ethical to intervene?
  • what os the target population?
  • what groups are needed?
  • how are the groups created?
  • is there evidence of a challenge?
  • what are the outcomes?
  • how big of a study would you need?
  • how do we avoid bias in follow-up?
  • statistical analysis
25
negative vs positive control group
negative: given nothing or a placebo is it better than nothing? positive: given the best possible current treatment is it better than the old treatment?
26
why are clinical trials stronger than case series
clinical trials include a comparative group
27
what are cross-over studies
- each individual is their own control - good for interventions that treat symptoms - mostly used for studying chronic diseases
28
the number of subjects needed in a trial increases with...
- smaller treatment effect (difference between groups) - larger variation among individuals - more covarieties - more groups - more clusters - longer duration
29
types of blinding
single blinded: either subject, observer or data analyst are blinded double blinded: 2 of the 3 are blinded triple blinded: all 3 are blinded
30
pros and cons of historical controls
pros: more practical/ethical, shorter duration cons: recall bias
31
what is a systematic review
a systematic approach to synthesize scientific evidence for a specific topic
32
what is a meta-analyses
a statistical method used to combine the results of various studies in the systematic review - can't do it without a systematic review first
33
benefits of systematic reviews
1. transparency 2. many studies considered simultaneously 3. can do meta-analyses
34
limitations of systematic reviews
1. garbage in, garbage out 2. selection bias 3. heterogeneity 4. publication bias and inclusion of "grey literature"
35
how do we measure disease frequency
counts: number of people with disease proportions: number with disease divided by population size rates: an expression of event occurrence in a defined population in a specified period of time ("per unit something")
36
what tool do we use to measure disease prevalence (existing cases)
proportions - ranges from 0-1 - only one measurement required
37
how do you calculate point prevalence
with disease at a single point in time / # in population that COULD have disease at that point in time
38
how do you calculate period prevalence
with disease during a specific time period / # in population that COULD have disease during that time period
39
what is censoring
when observation is stopped for some reason, could be - end of study - individual left cohort - lost to follow-up - death
40
why is prevalence NOT a measure of risk
it doesn't take into account when the disease occurred - only tells us how many individuals are affected
41
2 observations/tests required to measure incidence
1. establishes which individuals are disease free 2. identifies which ones developed disease in the observation period
42
what are the 2 ways to measure incidence
1. rate 2. risk - the numerator is the same for both - denominator differs
43
what is risk (aka cumulative incidence)
- proportion of unaffected individuals who will develop the disease of interest over a specified time period - PROPORTION, range 0-1
44
how do we calculate risk
of new cases during a time period / (initial # at risk - 1/2 withdrawals during that time period)
45
what is rate (aka incidence density)
- measures the average speed with which newly diagnosed cases of the disease develop - the denominator is the sum of units of time each individuals was at risk and observed
46
2 ways to calculate rates
numerator is number of new cases for both 1. exact denominator: know exact details for each individual 2. approximate denominator: only have summary data
47
calculating rate with exact denominator
of new cases in population surf specified time period / net time individuals in population ate at risk during that time
48
calculating rate with the approximate denominator
of new cases in population during specified time period / ( 1/2 x (initial NAR - final NAR) x internal time component)
49
what is an internal time component
time period in the denominator or rate calculations (e.g. person time)
50
interpreting incidence rate
... cases per person-year (or whatever component of time you are using)
51
general relationship between prevalence and incidence
prevalence is proportional to incidence x duration
52
what is case fatality rate
proportion of individuals with a specific disease that die as a result of that during a given time period of deaths among cases of x / # diagnosed cases of X
53
what is attack rate
used in outbreak investigations exposed people who got ill / total # exposed people
54
what is an outbreak
when 2 or more cases meet the case definition with a common epidemiological link and onset of symptoms within the same time period
55
steps involved in an outbreak investigation
- confirm the outbreak - develop outbreak case definition - case identification and management - epidemiological analysis - reporting the outbreak - investigating potential exposures - implementing control measures
56
what measures of association can we use to determine the most likely cause of an outbreak
odds ratio - generated from case-control studies risk ratio - generated Fromm cohort studies if OR or RR is > 1 then exposure increased the odds or risk of illness
57
types of epidemic curves
point source: exposure from a single event, majority of cases in one incubation period continuous source:ongoing exposure, not confined to one point in time propagated source: spread of pathogen from one susceptible individual to multiple intermittent source: exposure in spurts, is ongoing but intermittent
58

Epidemiology (3 decks)

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