Epidemiology and population health Flashcards
Describe the basic reproduction rate, R0
R0 = the average number of persons infected by one disease source.
R0 = C x P xD
C: the number of contacts of an infected person makes per unit of time
P: probability of transmission per contact
D: the duration the infected person is infective to others.
If the R0 > 1 the disease will continue to spread.
What does the infection cycle need?
source, host, and spread – amplification.
What is incubation period?
time between catching an infection and symptoms appearing. Varies between different diseases, e.g. rubella (14-21 days).
What is infectious period?
the time period during which an infected person is able to transmit the disease to a susceptible host or vector. Not necessarily associated with symptoms (chicken pox is infectious 1-2 days before symptoms appear.
What is latent period?
time between catching an infection and diagnostic signs of infection but still asymptomatic → when they are capable of infecting others
Define epidemic
affecting or tending to affect an atypically large number of individuals within a population, community, or region at the same time
Define outbreak
a sudden rise in the incidence of disease
Define pandemic
occurring over a wide geographic area and affecting an exceptionally high proportion of the population
Define attack rate
In epidemiology, an attack rate is the biostatistical measure of frequency of morbidity, or speed of spread, in an at risk population. An at risk population is defined as one that has no immunity to the attacking pathogen which can be either a novel or established pathogen. It is used to project the number of victims to expect during an epidemic.
Define secondary attack rate
the secondary attack rate measures the spread of disease within a household, or similarly limited situation. For example a specific rate could be used to evaluate the cause-specific mortality rate due to HIV for a particular group during a particular time.
What is a case report?
study of one individual with a disease, timely or rare information.
What is a case series?
study of several patients with similar symptoms. May lead to general hypothesis. No controls
What is an ecological trial?
at least one variable is measured at group level (e.g. sunlight exposure). The incidence of disease is compared in different groups. The unit of analysis is a population, not an individual. No info on each individual.
Usually used to measure prevalence and incidence of disease, particularly when disease is rare
What is a cross-sectional study?
measures exposure and disease in a study group at one time point (‘’snapshot’’). Frequently takes the form of a survey. Relatively inexpensive, studies often rely on data collected for other purposes.
- e.g. John Snow and cholera in London
What is a case-control study?
assesses whether historical exposure to one or more risk factors in people who have the disease (‘’cases’’) is comparable to that in people who do not have the disease (‘’controls’’). Retrospective study.
Process of case control study
Choose a well-recorded population containing some people who have or did have a precisely defined disease.
Hypothesise what may have caused illness or death
Select matched population who might have developed the pathology but didn’t
Looks back to compare how frequently the exposure to a risk factor is present in each group to determine the relationship between the risk factor and the disease
Compare the answers from the two groups.
Positives of case control studies
Good for rare disease
Relatively fast
Relatively inexpensive
Can look at the association between the disease of interest and many kinds of exposures.
Negatives of case control studies
Susceptible to bias
May be hard to find suitable controls
Time relations may not be clear
Associations that are revealed may not be causal.
What is a randomised control trial?
assess whether a cause-effect relationship exists between treatment and outcome.
What are the phases of clinical trials?
Phase 0: small number of participants and low dose of drug. Confirmation that drug behaves as expected from the laboratory research.
Phase 1: small trials, cohorts are treated with increasing doses of drug (dose escalation study). Safe dose? Side effects? Effect on the disease?
Phase 2: more patients involved. Best dose? How to manage side effects?
Phase 3: New treatment is compared to standard treatment. May involve thousands of patients because differences between treatments may be quite small.
Phase 4: after licencing the long term risks and benefits are studied on very large groups of people.