Epi Final Flashcards
Routine reporting for healthcare facilities and labs, cases present themselves over time.
Passive Surveillance
Example case scenario: passive surveillance
admitted patient testing positive for Covid-19
Public health researchers and clinicians seek out new cases
Active surveillance
Example case scenario: active surveillance
John Snow going from house to house to ask questions regarding cholera outbreak
Innate immunity, immunity through antibodies from another person or animal. Short duration
passive immunity
case scenario
baby born with antibodies from mother
immunity via vaccines, teaches body how to identify and ward off pathogens. longer duration, best for herd immunity
active immunity
person to person transmission, close proximity to one another
direct contact
direct contact examples
kissing, mother to baby via placenta or breastmilk
transmission via food, air, water, vector or vehicle
indirect transmission
non-living, inanimate object that carries infectious agents, vehicle born
fomite
how much potential agent can cause damage to the host
virulence
ability to spread to adjacent tissues
invasiveness
ability to cause damage to host cells
pathogenic potential
ability to infect, multiply and spread to new hosts
infectivity
Incidence rate equation
(# of new cases over period of time)/(average population at risk during same time) x 100,000
two epidemiological rates for open populations
incidence rate, incidence density
Incidence density equation
(# of new cases over specific period of time)/(person time)
sum total of all time contributed by all subjects
person time
measures the rate in which new cases of a health outcome develop in a population within a specific time
incidence
two epidemiological rates for closed populations
crude attack rate, cumulative incidence
Crude attack rate equation
(# ill with health outcome)/(total # of people at event) x100
cumulative incidence equation
(# of new cases over study’s time period)/(study’s sample at risk)
proportion of people who have the disease (existing and new cases) over a given period of time
prevalence
health outcomes that occur at a particular point in time relative to a specific population
point prevalence
heath outcomes that occur within a specific population over a period of time
period prevalence
does incidence depend on prevalence or vice versa?
prevalence depends on incidence
crude/annual death rate equation
(# of deaths from all causes in given year)/(total population) x100,000
disease specific death rate equation
(# of deaths due to certain disease)/(total population) x100,000
case fatality rate equation
(# of deaths due to disease)/(# of cases of disease) x100,000
age adjusted death rate equation
(# of deaths in age group)/(total population of age group) x100,000
maternal mortality rate equation
(# of deaths due to childbirth)/(total # live births) x100,000
infant mortality rate equation
(# of infant deaths)/(# of live births) x100,000
screening that focuses on high risk groups
selective screening
selective screening case scenario
screening for prostate cancer among individuals with a family history
screening of the population regardless of risk status
mass screening
mass screening case scenario
screening for Covid-19
Pros and cons of mass screening
pro: prevents mass onset/diagnosis of specific diseases
cons: expensive
pros and cons of selective screening
pros: less expensive
cons: can be challenging to get participation
concluding that something is true when it is false
false positive
concluding that something is false when it is actually true
false negative
reject the null hypothesis when we should fail to reject the null hypothesis
type 1 error, false positive
failing to reject the null hypothesis when we should reject the null hypothesis
type 2 error, false negative
a patient testing positive and having the disease
true positive
the proportion of diseased individuals who were correctly identified as positive, ability to identify who has the disease
sensitivity
sensitivity equation
of true positives/ total with disease
95% of the individuals with the disease are screened as true positives while the remaining 5% are true negatives
95% sensitivity
a patient testing negative and not having the disease
true negative
proportion of non-diseased individuals who were correctly identified as negative, the ability to correctly identify who does not have the disease
specificity
specificity equation
of true negatives/ total # without the disease
the probability that a patient with a positive test will have the disease
positive predictive value
as prevalence increases, positive predictive value ______
increases
the probability that a patient with a negative test will not have the disease
negative predictive value
as prevalence decreases, negative predictive value ______
increases
no evidence of disease, preclinical phase (no genetic changes or agent interaction with host), primary prevention (vaccines, health education)
pre-pathogenesis
potential signs and evidence of disease, subclinical phase (changes in genetic makeup, host has been exposed), secondary prevention (screening)
pathogenesis
disease is present, clinical phase (diagnosis of disease by physician), tertiary prevention (rehab, surgery)
late pathogenesis
answers who, where, and when
observational studies
exposures and risk factors assessed at group level, clusters (neighborhoods, hospitals, cities, states, countries)
ecological studies
pros and cons of ecological studies
pro: understanding disease occurrence across groups
cons: ecological fallacy (assuming association is the same for population and individual levels)
accounts of a single of small number of patients with various signs, symptoms, and health outcomes
case report
pros and cons of case report
pro: beneficial for observing symptoms among patients
cons: small number of individuals and effectiveness of treatment difficult to determine
case report scenario
exploring the side effects of a patient given a new drug for their asthma
ecological study scenario
assessing the occurrence of fatty liver disease between Nevada and Arizona
larger collection of cases among patients with a common characteristic
case series
pros and cons of case series
pro: can be linked to other health data, can help generate hypotheses based on collection of cases
con: obtaining information for specific cases among multiple patients can be time consuming
case series scenario
what is the average length of time that stroke patients admitted into the hospital stay before they are discharged?
an observational study that involves looking at data from a population at one specific point in time (measuring exposure and outcome at the same time)
cross-sectional study
pros and cons cross sectional study
pro: no wait time for disease to occur in population, assessing existing number of cases within population
con: not suitable for rare or highly fatal diseases, cannot determine if exposure preceded disease
age, sex, race/ethnicity, religion, health conditions, etc.
beneficial for utilizing characteristics that better define the population
person variables
regional differences within a nation that may affect prevalence and incidence of disease
climate, latitude, rural vs urban, county, neighborhood, state, country
place variables
gradual changes in the occurrence of disease over long periods of time
chronic illnesses
secular trends
what effects secular trends?
diagnostic techniques of diseases, changes in disease incidence rates (accuracy of denominator)
increases and decreases in the frequency of a disease or other phenomenon over a period of several years or within a year
allergies in spring, URI in winter, car accidents in rainy months
cyclic trends
focuses on the why and the how
analytical epidemiology
compare the number of people who have disease with number of those who do not. starts with disease and looks in the past for exposure variables.
retrospective case control study
pros and cons of case control study
pro: determines temporality (does exposure come before outcome), inexpensive, fast, does not need large study sample
con: recall bias, participant bias
individuals recruited in study are disease free at beginning, but have known exposure status
cohort study
exposed and non-exposed groups are known at the beginning of the study, moves forward in time. also known as longitudinal study
prospective cohort study
pros and cons retrospective cohort study
pros: information is immediately available
cons: recall bias, accuracy of records may be flawed, tracing subjects can be challenging
pros and cons prospective cohort study
pros: measure multiple health outcomes within a single study
cons: difficult to measure multiple exposures in single study, and for assessing rare or uncommon diseases, drop offs (drop out before end of study), more expensive and time consuming
These two professionals combined prospective and retrospective cohort studies regarding smoking
Doll and Hill
researcher is aware of the status of the disease at start of study.
beneficial for uncommon diseases
can only study one disease
case control study
researcher is aware of the status of the exposure at the start of the study.
beneficial for common diseases.
can study multiple diseases
cohort study
this study measures odd ratio
case control
this study measures relative risk
cohort study
designed to assess the effectiveness/safety of medical treatments and education.
subjects randomly assigned to control or test group
participants chosen randomly
intervention controlled by the investigator
randomized controlled study
pros and cons of randomized controlled study
pros: equal chance of being selected, greatly reduces biases (selection, information, confounding), facilitates blinding
cons: groups may have different # of participants, more time and money, groups may not reflect entire population, dropouts/loss of follow up, drop-ins
group members can remain within start group or switch through process known as crossover design (washout period must occur to reduce side effects)
crossover randomized controlled study
study conducted with means of avoiding researcher bias
blinding or masking randomized controlled study
participant is unaware of what group they belong to
single blinded
participant and researcher are unaware of what group they belong to
double blinded
clinicians, data collectors, and analysts are all
triple blinded
pros and cons of blinding/masking randomized controlled trial
pros: minimizes bias
cons: costly and time consuming
9 steps and phases of randomized controlled trials
1: Preclinical
2: drug is approved for testing in humans
3: phase 1 (20-80 participants)
4: phase 2 (100-300 participants)
5: phase 3 (1,000-3,000 participants)
6: drug submitted for FDA approval
7: FDA review to confirm safety and effectiveness
8: drug is approved
9: phase 4 (1,000+ participants)
steps for completing randomized controlled trial
1: decide objective and phase of the study
2: decide who members of study population will be and how they will be recruited
3: choose blinding method
any quantity that can have different values across individuals or study units that are associated with one another
variables
if value of one variable increases, the value of the other increases
positive association
if the value of one variable increases, the value of the other decreases
negative association
measuring the odds of exposure among cases and controls
odds ratio
odds of the exposure among cases are greater than the odds among the controls
odds ratio greater than 1
odds of the exposure among cases are the same as the odds among controls
odds ratio equal to one
odds of the exposure among cases are less than the odds among controls, protective factor (individual is not at risk of being diagnosed with disease)
odds ratio less than one
what does an odds ratio of 1.62 mean?
the odds of smoking is approx. 1.62 times higher among CHD cases compared to non-CHD cases
what does an odds ratio of 0.62 mean?
the odds of smoking is 38% (1-0.62) less likely among CHD cases compared to non-CHD cases
the ratio of incidence rate of the disease within the exposed group compared to the ratio of incidence rate of disease within the non-exposed group
relative risk
relative risk equation
(A/A+B)/(C/C+D)
exposure variable is a risk factor for the disease
relative risk greater than 1
there is no association between the exposure variable and the disease
relative risk equal to 1
the exposure variable decreases the risk of the disease, protective effect
relative risk less than 1
relative risk of 1.38 means?
risk of developing CHD is 1.38 times higher among smokers than non-smokers
incidence rate in the exposed group minus the incidence in non-exposed group
attributable risk
how would you interpret an attributable risk of 10.6?
10.6 of the incidence cases of CHD can be contributed to smoking
