Epidemiology Flashcards
Time-Space clustering
distribution of disease occurs in patterns in a community
Patterns of disease is
predictable
Characteristics of the disease patterns may lead to
prevention or control of disease
Epidemiologic Triad
Host - Agent - Environment; all 3 must be present and favorable for an infection to occur
Host factors
biological traits (genetics, sex, age, ethnicity), social traits (behavior, nutrition, lifestyle, residence)
Agents of disease
biological, chemical, nutritional, physical, energy
Pathogenicity
ability to produce disease in a host
virulence
to what extend can a pathogen cause disease (genetic, biochemical, structural)
The outcome of an infection is determined by
the virulence of the pathogen and the resistance of the host
vectors
biological means of spreading disease (insect)
fomite
mechanical means of spreading disease (toilet seat)
Herd Immunity
the spread of communicable disease within a group based on the proportion of susceptible and immune individuals
What proportion of the population must be immune to maintain herd immunity?
dependent on the disease and the mode of transmission, higher for respiratory modes of transmission
Physical factors
location of reservoir (where agent thrives), biologic factors (presence of arthropod/vector), mechanical vector (on feet of flies), biological vector (ticks), social factors
Endemic
disease of humans present in a particular region at essentially constant levels
Epidemic
sudden increase in the incidence of a particular disease
Common source epidemic
all individuals are expose to pathogens from one common source
Point source epidemics
all individuals are exposed to a pathogen during one point in time
Propagative epidemics
serial transmission of an agent
Pandemic
pandemics at a large scale (worldwide)
Primary prevention
preventing disease before it occurs (sunscreen)
Secondary prevention
catching a disease early (removing suspicious lesion)
Tertiary Prevention
treating person with disease to get them healthy quicker
Incidence
number of new cases reported during a specific time period (communicability and incubation time)
Incidence rate
number of new cases with in a population in a defined time period / number of persons exposed in the same time period
Incidence rates can be used to estimate
frequency (communicability) and incubation time
Frequency
communicability; rate of disease transmission/time period
Incubation period
time from exposure to time of onset of symptoms
Incidence is
time dependent
Attack rate
number of people ill / number of persons exposed during an outbreak
Primary case
first case of disease in population
index case
first case brought to attention of epidemiologists
Secondary attack rate
percentage of people among close contacts of primary case who become ill
Prevalence
incidence (new cases) + old cases
Prevalence gives information about
the percent of disease in a population at one time; does not confer information about incubation period, rate of disease transmission, frequency of occurence
What number directly impacts the predictive value of diagnostic tests
prevalence
point prevalence
amount of disease present in a population at a time point (1300 TB cases / 130000 population = 1%)
Point prevalence is helpful to
compare points of time, is prevalence increasing or decreasing
Period prevalence
the number of people with the disease within the given time frame / population
Factors that increase the prevalence rate
immigration of ill people or potentially exposed people, emigration of healthy people, increased incidence, increased duration of disease
Prevalence is decreased by
increased death rates, shorter duration of disease, ill exiting, health entering
If point prevalence AND incidence increase:
disease increases due to increased virulence or decreased treatment
If point prevalence increases and incidence stays the same
recovery from disease slows, disease is less fatal ( anything that keeps ill people around longer)
If point prevalence decreases and incidence stays the same
recovery from a disease speeds up or is more fatal (anything that takes ill people away faster)
If point prevalence remains the same, but incidence drops
Prevention is occurring, but disease recovery is long-term
If point prevalence remains relatively the same, but incidence is dropping significantly
Prevention of disease, but no cure (herpes)
If point prevalence decreases and incidence decreases
spread of disease declines and recovery is permanent, disease is highly fatal
Sensitivity
how good test is at picking up people who have this disease… True positive rate
Specificity
how good this test is at at excluding people without the condition… true negative rate
PPV
If test comes back positive, likelihood patient does have disease
NPV
If test comes back negative, likelihood patient does not have disease
