Lectures 3-7: Descriptive Epidemiology; Measures of Disease Frequency Flashcards
Descriptive Epidemiology
the Person (WHO), Place (WHERE, Time (WHEN) regarding disease occurrence
Case definition
a set of uniform criteria used to define a disease/condition for public health surveillance (like diagnostic criteria in a clinical setting)
Epidemic
occurrence of disease clearly in excess of normal expectancy
Outbreak
an epidemic limited to a localized increase in the occurrence of disease (may be interchanged with “cluster”)
Endemic
constant presence of a disease within a given area or population in excess of normal levels in other areas
Pandemic
epidemic occurring over a very wide area involving a large number of people - many times multi-region or multi-national
Ratios
Division of 2 unrelated numbers (numerator not part of denominator)
Proportions
Division of 2 related numbers (numerator is a subset of denominator)
Rates
Division of 2 numbers with TIME incorporated into the denominator
Absolute difference
Raw subtraction between two variables
ex: # live births - # total deaths in community
Adjusted disease/mortality rates
representation of rates of disease or death among total population, generally adjusted to reflect an appropriate population (such as age-adjusted rates)
ex: age-specific mortality rate: # of deaths of specific age group from any cause / 100,000 people per year
Attack rate
new disease cases that develop/# healthy population at risk for disease
*We would have to subtract individuals already diseased or vaccinated in this case
Case fatality rate
cause specific deaths/# cases disease
Cause-specific morbidity rate
diseased by specified cause/total population
Cause-specific mortality rate
cause-specific deaths/total population
Cause-specific survival rate
specific cases alive/# cases of disease
Common source outbreak
outbreak in which a group of people were all exposed to a disease or toxin at the same time
Crude morbidity rate
people with disease/total population
Crude mortality rate
deaths/total population
Cumulative incidence
new cases of disease/# in candidate population over specified period of time
Fertility rate
live births/1,000 women of childbearing age
Incidence
new cases/# persons at risk for disease
*subtract out those not at risk
Incidence density
new cases of disease/total person-time in population at risk for disease
Incidence rate
new cases of disease/person time at risk for disease
Incubation period
amount of time from exposure to symptom presentation
Induction period
time between exposure to risk factor and initiation of disease
Infant mortality rate
of deaths in those less than 1 year old/1000 live births
Infectivity
individuals infected/# individuals susceptible
Latency period
time between biologic onset of disease and disease detection
Live birth rate (Natality)
live births/1,000 population
Maternal mortality rate
female deaths related to pregnancy/100,000 live births
Morbidity
disease, usually as a rate or proportion of those with disease
Neonatal mortality rate
deaths in those less than 28 days old/1000 live births
Pathogenicity
with clinical diagnosis of disease/infected individuals
Period prevalence
prevalence over a given period of time
ex: during 2012, over 1 year
Person-time
accounts for the amount of time each person was followed during the study
ex: 100 person-years = 100 people followed over 1 year, 10 people followed for 10 years each, etc
Propagation outbreak
outbreak which spreads from person-person, infects others (present as repeated spikes on epi curve)
Point source outbreak
outbreak in which infected persons were exposed to disease in a single event (such as a meal); curve rises rapidly and falls gradually (present as a bell curve-like blob on the epi curve)
Postnatal mortality rate
deaths in those older than 28 days, but less than 1 year/1000 live births
Prevalence
of existing cases of disease/# at risk or base population
Prevalence rate
incorporates time into prevalence
Point prevalence
prevalence at a specific point in time
ex: prevalence on January 1st
Proportional Mortality Rate (PMR)
cause specific deaths/total # deaths in population
Relative difference
ratio of 2 measures of disease frequency (divide them)
Risk
Same as incidence; # new cases/# population at risk for disease
Secondary attack rate
new cases of disease among contacts/# contacts
Sentinel/Index case
original/1st case known (stands alone at beginning of epi curve)
Survival rate
that survived/# infected
Virulence
deaths/# individuals with disease
What key factors are needed to compare measures of disease frequency between groups?
- # of people affected/impacted (frequency)
- Size of source population or those at risk
- Length of time population is followed
