STA20009 Epidemiology Flashcards
LIST: Objectives of modern epidemiology
- Description
- Causation
- To apply and evaluate interventions
- To study the natural history and prognosis of disease
- To provide the foundation for public policy
LIST: Types of epidemiology
- Descriptive studies (person, place, time)
- Analytic studies (causation and association)
- Intervention studies (evaluating and monitoring)
EXPLAIN: Epidemiological triad
Host, agent, and environment all interact with each other and the vector
LIST & DEFINE: each component of the epidemiological triad
Host: organism
Environment: surroundings and conditions, that may be promoting disease spread e.g. unclean water, crowding
Agent: cause of the disease e.g. virus, bacteria, parasite, fungus etc
Vector: carry agents from infected source to host or host’s food or environment
LIST AND PROVIDE EXAMPLES: modes of transmission
Direct e.g. physical contact, exchange of body fluids
Indirect e.g. sharing contaminated food or towels, airborne, vector i.e. an animal
STATE: attack rate formula
AR = n at risk who develop disease/total n at risk
DEFINE: primary case
Person who acquires disease from direct exposure
DEFINE: secondary case
DEFINE: secondary attack rate
AR in susceptible individuals exposed to primary case
STATE: the difference between signs and symptoms
Symptoms: subjective indications of disease reported by the person
Signs: objective indications of disease apparent to physician
DEFINE: prevalence
Proportion of people in a population who have the disease at a given point in time
CALCULATION: prevalence
number of people with disease at a given point in time / total number of people in the population at that time
CALCULATION: period prevalence
number of people with disease during certain time period (including at start of period, and anyone who develops it during the period) / total number of people in the population at that time
DEFINE: incidence
new cases of disease in population
IDENTIFY: most common study design for measuring incidence
cohort study
IDENTIFY: most common study design for measuring prevalence
cross-sectional study
CALCULATION: incidence rate
number of people who develop disease in a year / avg number of people in the population in the same year
COMPARE: incidence rate and incidence proportion (cumulative incidence)
IR sometimes compares incidence to number of people in the population whereas IP only compares incidence to population at risk
In other words…
Incidence proportion measures risk or probability of getting disease whereas incidence rate measures how quickly (the rate at which) cases occur
CALCULATION: incidence proportion
IP = number of people who develop disease in a specified period / number of people at risk of getting the disease at the start of a period
CALCULATION: incident rate/incident density per person-time
number of people who develop disease in one year / number of person-time when people were at risk of getting disease
DEFINE: person-time at risk
The amount of time people were at risk for developing the disease
(When someone develops the disease, they are no longer at risk, so no longer contribute to person-time)
CALCULATION: relationship between incidence and prevalence
P(approx) = IR x D
P = prevalence
IR = incident rate
D = duration of disease
