Summary Study Epi Flashcards
Attributable Risk (AR)- what is the question it answers? What is AR useful for?
How much disease amongst those exposed is due to the risk factor?
This is good for policy making because it gives an estimate of the absolute amount of disease associated with exposure. i.e. asbestos and dogs- reducing the exposure will not have a big impact on animal health in Australia because there are very few cases every year
Attributable Fraction of the exposed (AFexp)- what is the question it answers? When is AF useful?
What percent of disease amongst the exposed is due to the risk factor?
AF is useful because it conveys a sense of how much disease in the exposed population can be prevented by blocking the effect of the exposure or eliminating exposure.
Population Attributable Risk (PAR)- what is the question it answers?
How much disease in the population is due to the risk factor?
Population Attributable Fraction (PAF)- what is the question it answers? What does the magnitude of PAF for a given exposure depend on (2 things)?
What percent of disease in the population is due to the risk factor?
The magnitude of the PAF for a given exposure depends on:
1. the prevalence of exposure
2. The strength of association between the exposure and the outcome
** Even if we have an exposure that is strongly associated with an outcome, removing it will have little effect on disease risk in the population if its prevalence is very low
Pathogenicity
The ability of an agent to produce disease in an infected host
Virulence
The ability of an agent to produce severe disease
Incubation period
The interval between effective exposure to an infectious agent and the appearance of the first sign of disease in question
Latent period, also called? What is it?
Prepatent period. The interval between infection to shedding of the infectious organism.
Host
An animal capable of being infected with an infectious agent. Replication or development typically occurs in the host.
Carrier
An infected animal that harbours a specific infectious agent in the absence of discernible clinical disease and serves as a potential source of infection for other animals.
Induction period
The time from exposure to the agent to the first appearance of disease with a non-infectious agent e.g. cancer
What are drivers of disease spread?
Agent, host, environment
What are factors that affect a propagating epidemic curve?
The incubation period (can cause waves, delay start, prolong outbreak), infectious period, infectivity of the agent, the proportion of susceptible animals in the population, animal density, surveillance efficiency, reporting practices and the validity of diagnostic tests
What is antigenic drift?
An agent (such as influenza) that can mutate rapidly, evading humoral immune response, leading to antigenic drift- which produces new strains which may be more pathogenic or highly virulent. “Vaccine arms race”
What is antigenic shift?
Different strains of an agent (such as influenza) if they infect the same host can reassort and swap parts of its segmented genome, leading to new strains. This can lead to pandemics since the population will be naive and can also lead to a species jump.
What is the effective reproductive ratio (R)?
Represents the average number of secondary infections produced by each infected individual that enters a population that contains non-susceptible animals or is subject to disease control measures (i.e. as an outbreak progresses).
What are two factors that cause epidemics to die out?
A low rate of effective contact (c x p) and a reduced proportion of susceptible animals (St/N)
What effect does herd immunity have on an epidemic?
An increase in herd immunity leads to the peak of an epidemic can be delayed and /or the magnitude and duration can be greatly reduced
What is herd immunity?
The resistance of a population to attack by disease in which a large proportion of members are immune, thus lessening the likelihood of an animal with disease coming into contact with a susceptible individual.
What is the herd immunity threshold?
The proportion of the population that needs to be immune in order to reduce the incidence of disease
If herd immunity is greater than 75%, what does this mean for an infectious disease?
The infectious disease is often not able to propagate unless R naught is greater than 4.
What are the two parts of a good case definition?
- It specifies the characteristics of the population at risk
- It specifies what distinguishes cases from other members of the population
Why are rates preferred to ratios?
Because they are measures of risk and there is a time period specified.
Is incidence or prevalence the preferred measure of morbidity?
Incidence because prevalence is affected by both duration and incidence rate of disease, so direct interpretation of prevalence is difficult.