Lecture 2: Epidemiology Flashcards
Define epidemiology.
The study of distribution and determinants of health-related states among specified population and the application of that study to the control of health problems
What do epidemiologists do?
- Discover the agent, host, and environmental factors that affect health
- Determine the relative importance of causes of illness, disability, and death
- Outbreak investigation
- Identify at-risk segments of the population
- Evaluate the effectiveness of health programs and services in improving population health
What are the 2 types of studies?
- Experimental
- Observational
Define an experimental study.
Intervention in the disease process and study the effect of intervention
- Study therapeutics or vaccines in a population
Define an observational study?
No intervention, just observation of diseases process
Define cluster.
A group of cases linked by time or place, but with no identified agent or common source
Define outbreak.
Sudden increase in number of cases beyond normal (baseline) typically within a small area
Define epidemic.
A sudden large increase in number of cases within a specific geographic area
Define endemic.
Regularly present within a geographic area
Define pandemic.
Epidemic that has spread across international borders and affects large regions and large amounts of people
Explain the disease triangle.
Simplified conceptual model that shows the interaction of 3 factors/conditions in causing disease or epidemics/outbreaks
- All 3 conditions must be present and favor disease
Explain the role of the pathogen in the disease triangle.
A pathogen must have the ability to establish an infection to cause disease (virulence)
Define infective dose.
Number of cells required to successfully infect a host
Define virulence factors.
Molecules, proteins, or structures that promote infection
What does attenuated mean?
A reduction in virulence to a point where it non longer causes disease
What is the role of the host in the disease triangle?
A host must be susceptible
- Must be able to support the infection
- No immunity or insufficient immunity; immunocompromised
- Physiological diseases or disorders
- Trauma
- Behavior
What is the role of the environment in the disease triangle?
The surroundings and conditions must favor transmission
- Host availability
- Reservoirs and vectors
- Physical features
- Resources
What is the chain of infection?
Set of 6 intertwined links that allow for communicable diseases to spread
What is a reservoir (chain of infection)?
Any person, animal, plant, soil, or substance in which an infectious agent normally lives and multiplies
How can you intervene with the reservoir?
Eliminate or quarantine the reservoir
What is the port of exit (chain of infection)?
How pathogens leave the reservoir/current host
How can you intervene with the port of exit?
- Masks
- Sewage systems
- Condoms
- Bandages
What are modes of transport/transmission (chain of infection)?
The movement of the pathogen to a new host
- Direct vs indirect
Describe direct transmission.
Transmitted directly from reservoir/current host
- Direct contact
- Droplets that don’t stay in the air too long
- Airborne (host still present)
Describe indirect transmission.
Current infected host doesn’t have to be present to transmit
- Airborne (after current host is gone)
- Vectors and vehicles
How can you intervene with direct transmission?
- Air filters
- Social distancing
- Gloves
- Protective equipment
How can you intervene with indirect transmission?
- Pest control
- Filtration
- Ventilation
- Sanitation
- Food safety
Describe port of entry/exposure (chain of infection).
How a pathogen enters a host
- Ex. mucous membranes, skin, blood transfusions
How can you intervene with port of entry/exposure?
- Masks
- Bandages
- Hand washing/personal hygiene
- Protective equipment
How can you intervene with a susceptible host?
- Vaccinations
- Pre-exposure prophylaxis
- Post-exposure prophylaxis
- Exposure risk assessments in CDC website
What are the 5 stages of the disease process? Briefly describe each.
- Incubation period: time between exposure and signs/symptoms
- Prodromal stage: short period with first signs/symptoms
- Period of invasion/illness: most evident symptoms
- Decline: immune system at peak
- Convalescent period: recovery
Define infectious period.
The time when a person can transmit the virus
Define carrier.
A colonized or infected host with no clinical illness but can transmit
What is the importance of the infectious period?
Important when it comes to contact tracing and quarantine
Define basic reproductive number (R0).
The expected number of secondary cases produced by a single typical infection in a completely susceptible population
- Indicator of the contagiousness of a disease
What is the formula for R0?
transmissibility x average rate of infection x infectious period
What is transmissibility?
Probability of infection
What does a an R0 of <1 mean?
That the epidemic will eventually die out
