Infectious Disease Epidemiology

Question 1

What is the crude rate?

Answer 1

deaths / # of people at risk of dying

Question 2

Why is the age adjusted rate useful?

Answer 2

it allows for comparison between geographic areas w different proportions of older people who are more likely to die from infections

Question 3

What is this:

of deaths (age specific) / # of people at risk of dying (age specific)

Answer 3

age specific rate

Question 4

What is this:

deaths due to cause x, time t / # All deaths during same time

Answer 4

proportionate mortality

Question 5

When is case mortality rate useful?

Answer 5

When you want to compare different diseases or different strains of diseases

Question 6

How do you carry out an outbreak investigation?

Answer 6

1. Is it real?
2. Confirm the diagnosis
3. Assemble the team
4. Develop case definition
5. Count: person, place, time
6. Develop hypothesis
7. Introduce preliminary control measures
8. Design study to test hypothesis
9. Communicate findings
10. Surveillance and monitoring

Question 7

What can happen to the case definition as more and more info is revealed about an outbreak?

Answer 7

It can change!

Question 8

What is this?

Count back 1 day from first reported case and 12 days from the last case

Answer 8

incubation period

Question 9

What is this?

of new cases among population during the period / population at risk at the beginning of the period

Answer 9

attack rate

Question 10

What is the attack rate?

Answer 10

a measure of the probability or risk of becoming a case

Question 11

When is the attack rate useful?

Answer 11

to examine if the course of current outbreak is similar to other outbreaks; to examine vulnerable subgroups

Question 12

What is this?

of cases among contacts of primary cases during the period / total number of contacts *100

Answer 12

secondary attack rate

Question 13

What is this?

The unchecked progression of disease in an individual

Answer 13

natural history of disease

**vital for disease prevention policies

Question 14

What is the most effective tool we have to control infectious diseases?

Answer 14

vaccination

Question 15

Permanent reduction to zero of the worldwide incidence of infection caused by a specific agent; intervention measures are no longer no longer needed

Answer 15

eradication

Question 16

The specific infectious agent no longer exists in nature or the laboratory

Answer 16

extinction

Question 17

Why is eradication of measles possible?

Answer 17

1. no animal reservoir of the virus

2. there is an effective vaccine

Question 18

What is the SIER framework for infectious disease?

Answer 18

Susceptible
Exposed: infected but not infectious
Infectious: able to transmit pathogen to others
Removed: immune individuals who aren’t at risk of further transmission

Question 19

What component is between Susceptible state and Exposed state?

Answer 19

force of infection

Question 20

What component is between Exposed state and Infected state?

Answer 20

Rate of progression to infectious state

*1/latent period

Question 21

What component is between Infected state and Removed state?

Answer 21

Rate of recovery

*1/infectious period

Question 22

Expected number of cases caused by a typical infectious individual in a susceptible population.

Answer 22

Basic reproductive number

Question 23

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?

Answer 23

it dies out; disease can invade

Question 24

What is the formula for calculating R0?

Answer 24

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

Question 25

What is this?

Average number of secondary infections produced by a typical infective index case

Answer 25

effective reproduction number R

Question 26

What is the equation for effective reproductive number?

Answer 26

R = R0 * S (the proportion susceptible to infection)

Question 27

What happens if R is greater than 1? Less than 1?

Answer 27

If R>1, number of cases increases

If R<1, number of cases decreases

Question 28

To achieve elimination, what must happen to R?

Answer 28

R must be maintained at less than 1

Question 29

The object of any infectious disease control program is to reduce the net reproduction rate below (blank), thereby causing a progressive decline in disease

Answer 29

1

Question 30

What is the equation for R effective?

Answer 30

R effective = R0 *S/N

Question 31

The critical proportion of the population that needs to be immune is determined by what calculation?

Answer 31

S/N < 1/R0

Question 32

Is there herd immunity for non-infectious diseases?

Answer 32

no

Question 33

How do you determine the number of individuals in a population who need to be immunised in order to achieve immunity?

Answer 33

it varies and depends on factors like the effectiveness of the vaccine and characteristics of the disease

Question 34

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

Answer 34

herd immunity