Lecture 2: Descriptive Epi & Frequency Flashcards
Frequency refers to….
Counts of disease occurrence within a specific population
Patterns of disease refers to….
Person
Place
Time
Descriptive epi-3W’s
What are the three types of surveillance systems?
Passive
Active
Syndromic
Healthcare worker reports to the CDC when a new case of ebola surfaces
Example of passive surveillance
An EIS worker is sent to Kansas City to investigate the outbreak of swine flu
Example of active surveillane
Define syndromic surveillance
A system that tracks specific signs/symptoms
Typically associated with rare diseases/conditions
What does the biosurveillance system focus on?
Humans, animals and plants alike
Name the four stages of the disease timeline
Susceptibility
Subclinical
Clinical
Recovery or Death
What causes you to move from the susceptibility stage to subclinical?
Exposure to disease
What does it mean to be subclinical?
You have been exposed to the disease, under going pathological changes but are pre-symptomatic
Meaning you have not shown any symptoms yet
What causes you to move from subclinical to clinical stage?
The onset of symptoms
In what stage and region of that stage does time of diagnosis fall?
Within the early clinical stage
What occurs in the final stage of the disease timeline?
Recovery
Disability
Death
Define induction period
Time between exposure and onset of disease
Also called incubation period
The time between exposure to a disease and onset of symptoms
Incubation period
Or
Induction period
Time between onset of disease and diagnosis
Latency period
Define latency period
Time between onset of symptoms and diagnosis
What do you think is the most critical element that must be defined before any of the ‘who’ of descriptive epidemiology can be acquired?
Case definitions
What are we looking?
What is the criteria someone must meet to be considered diseased?
What do these questions represent?
Case definitions
Define ‘case definition’
A set of criteria used to define a disease for public health surveillance
Enabling us to define a disease across nations and globally
What does CSTE stand for
Council of state & territorial epidemiologists
What does CSTE recommend?
That state health departments report occurances of specific diseases to the CDC’s NNDSS
What does NNDSS stand for?
National notifiable disease surveillance system
NNDSS is a department of what organization?
CDC
What does the NNDSS do?
Collects the reports from health departments on occurrences of a specific list of diseases
How often are case definitions updated?
Annually
Explain why it is important to have case definitions
We must always clearly define our diseases so that we can communicate across departments and across nations. So we know we are talking about the same thing
What is the difference between a confirmed and probable case?
Lab tests have confirmed diagnosis
Lab tests are not yet in but the patient has all the symptoms of a certain condition
Occurrence of a disease that is clearly higher than normal within a specific population
Epidemic
An epidemic limited to a specific region
Outbreak
A specific region where the prevalence of a specific disease is always higher than surrounding regions or other countries
Endemic
Pre-pandemic labeling
Emergency of international concern
A global alert due to an epidemic, alerting departments to be vigilant and to take preventative actions
Emergency of international concern
An epidemic that spread world-wide
Pandemic
A visual representation of measures of disease frequency
The Epi-curve
Name the two patterns of disease
Point source
Or
Propagated
Define ‘point source’
Disease is derived from a single point
Not person-person transmission
Define ‘propagated source’
Person to person transmission
What do the index case and sentential case have in common?
They’re the same thing = patient zero
What are the three types of relative measures?
Proportion
Ratio
Rate
Which type of measure has time incorporated into it?
A rate
What is the difference between a proportion and ratio?
Proportion = division of 2 related numbers
Ratio = division of 2 unrelated numbers
What are the 3 key factors when comparing multiple groups
of people in each population
Size of the people at risk
Length of time the population is ‘followed’
An example of how to standardize population size and time
Person-years
All new cases
Incidence
All existing cases + new cases
Prevalence
What do incidence and prevalence have in common relative to their formulas?
Same denominator
The at risk population
How to calculate incidence
of new cases/at risk population
What is cumulative incidence
The summation of incidences over multiple periods of time
Why do we not count a relapse in disease by one person? Why is said person only counted the first time?
Because we would have to adjust the denominator every-time a person got the disease again. It is impossible to keep track of everyone
How to calculate incident rate
of new cases
———————-
Person-time at risk
Define incidence density
Summation of incidence rate over multiple time periods
What do we do with repeat cases?
We only count them once
How to calculate prevalence
of existing cases
————————
Entire population at risk
What are the two types of prevalence?
Point - a specific point in time
Period - a specific time period - typically one year
of persons with disease
———————————
Entire population
Crude morbidity rate
of deaths from all causes
———————————-
Entire population
Crude mortality rate
of persons with a specific disease
———————————————-
Entire population
Cause-specific morbidity rate
of deaths from a specific disease
———————————————-
Entire population
Cause-specific mortality rate
# of cause-specific deaths ———————————- # of people with that disease
Case-fatality rate
# of people with a disease ———————————- # of cases of that disease (dead and alive)
Cause-specific survival rate
# of cause-specific deaths ———————————- # of deaths in entire population (all causes)
Proportional mortality rate or PMR
How are all measures of disease frequency in infants similar?
All are standardized per 1,000
What is the difference in infant mortality rate and maternal mortality rate?
Infant is standardized per 1,000
Maternal is standardized per 100,000
of live births/ 1,000 population
Live-birth rate
What is the equation for fertility rate?
# of live births ———————————— # of women of childbearing age (15-44)
of deaths <28 days old
———————————-
1,000 live births
Neonatal mortality rate
of deaths >28 days but <1 year old
————————————————
1,000 live births
Postnatal mortality rate
of deaths <1 yr old
——————————
1,000 live births
Infant mortality rate
How to calculate Maternal Mortality Ratio? And what is it specific to?
of female pregnancy deaths
——————————————
100,000 live births
Specific to female deaths due to their pregnancy itself
Why are the frequency rates referred to as rates yet there is not time represented in their equations?
Assumed to be annual rates (1 year)
What is infectivity?
How to calculate?
Ability of something to invade a host
infected/# at risk
What if pathogenicity?
How to calculate?
Ability of something to cause a clinical disease
# of people w/ disease —————————— # of people infected
What is virulence and how to calculate?
Ability of something to cause death
deaths/# of people with that disease
