Infectious Disease Epidemiology Flashcards
What is the crude rate?
deaths / # of people at risk of dying
Why is the age adjusted rate useful?
it allows for comparison between geographic areas w different proportions of older people who are more likely to die from infections
What is this:
of deaths (age specific) / # of people at risk of dying (age specific)
age specific rate
What is this:
deaths due to cause x, time t / # All deaths during same time
proportionate mortality
When is case mortality rate useful?
When you want to compare different diseases or different strains of diseases
How do you carry out an outbreak investigation?
- Is it real?
- Confirm the diagnosis
- Assemble the team
- Develop case definition
- Count: person, place, time
- Develop hypothesis
- Introduce preliminary control measures
- Design study to test hypothesis
- Communicate findings
- Surveillance and monitoring
What can happen to the case definition as more and more info is revealed about an outbreak?
It can change!
What is this?
Count back 1 day from first reported case and 12 days from the last case
incubation period
What is this?
of new cases among population during the period / population at risk at the beginning of the period
attack rate
What is the attack rate?
a measure of the probability or risk of becoming a case
When is the attack rate useful?
to examine if the course of current outbreak is similar to other outbreaks; to examine vulnerable subgroups
What is this?
of cases among contacts of primary cases during the period / total number of contacts *100
secondary attack rate
What is this?
The unchecked progression of disease in an individual
natural history of disease
**vital for disease prevention policies
What is the most effective tool we have to control infectious diseases?
vaccination
Permanent reduction to zero of the worldwide incidence of infection caused by a specific agent; intervention measures are no longer no longer needed
eradication
The specific infectious agent no longer exists in nature or the laboratory
extinction
Why is eradication of measles possible?
- no animal reservoir of the virus
2. there is an effective vaccine
What is the SIER framework for infectious disease?
Susceptible
Exposed: infected but not infectious
Infectious: able to transmit pathogen to others
Removed: immune individuals who aren’t at risk of further transmission
What component is between Susceptible state and Exposed state?
force of infection
What component is between Exposed state and Infected state?
Rate of progression to infectious state
*1/latent period
What component is between Infected state and Removed state?
Rate of recovery
*1/infectious period
Expected number of cases caused by a typical infectious individual in a susceptible population.
Basic reproductive number
If basic repro number, R0 is less than 1, what happens to the disease? If R0 is greater than 1, what happens to the disease?
it dies out; disease can invade
What is the formula for calculating R0?
Multiply the following:
C (number of contacts the infected person makes per unit time)
P (the prob of transmission per contact w the infected person)
D (duration that the infected person is infectious to others)
CPD = R0
What is this?
Average number of secondary infections produced by a typical infective index case
effective reproduction number R
What is the equation for effective reproductive number?
R = R0 * S (the proportion susceptible to infection)
What happens if R is greater than 1? Less than 1?
If R>1, number of cases increases
If R<1, number of cases decreases
To achieve elimination, what must happen to R?
R must be maintained at less than 1
The object of any infectious disease control program is to reduce the net reproduction rate below (blank), thereby causing a progressive decline in disease
1
What is the equation for R effective?
R effective = R0 *S/N
The critical proportion of the population that needs to be immune is determined by what calculation?
S/N < 1/R0
Is there herd immunity for non-infectious diseases?
no
How do you determine the number of individuals in a population who need to be immunised in order to achieve immunity?
it varies and depends on factors like the effectiveness of the vaccine and characteristics of the disease
describes a form of immunity that occurs when the vaccination of a significant portion of a population provides a measure of protection for individuals who have not developed immunity; this is the most effective way of protecting people who do not respond to vaccines or can’t be given them for medical reasons
herd immunity
