Infectious disease models

Question 1

What is a model

Answer 1

A representation of the real world, good=reliable representaion
based on assumptions

Question 2

In may and andersons STI transmission dynamics model what is the reproductive rate of an sti defined as

Answer 2

B=likelihood of transmission per sexual contact between an infected person and a susceptible partner
C= average number of new sexual partners formed over time between infected and susceptible people
D=average duration of infectiousness
BCD

Question 3

How cn the reproduction rate of an STI be redcuced

Answer 3

reduce the duration of infectiousness (detection and treatment)
reduce transmission efficiency (condoms)
reduce no. of sexual partners

Question 4

What are deterministic models of infection

Answer 4

describe what happens on average in a pop, assume that parameters such as rate of disease onset or rate of recovery are fixed

Question 5

What is a stochastic model of infection

Answer 5

Allow for random variations in parameters

Question 6

What are the three main considerations when constructing an infectious disease model

Answer 6

the natural history of infection
the accuracy and time period over which the model predictions are required
the research question

Question 7

What is an example of an SI model

Answer 7

HIV

Question 8

What is an example of an SIS model

Answer 8

Sexually transmitted diseases

Question 9

What is an example of an SIR model

Answer 9

for immunising infections like chicken pox

Question 10

What is an SEIR model

Answer 10

immunising infections with an added exposed/pre-infectious stage

Question 11

What is an example of an SIRS model

Answer 11

pertussis and influenza, where changes in immunity may occur due to occurance of a new circulating strain

Question 12

How can models be used

Answer 12

yeild predictions about spread of epidemic

plan health services (beds, drugs, prevention, mitigation, immunisation thresholds)

Question 13

What is the difference between secondary attack rate and basic reproductive rate

Answer 13

Proportion of infected among those susceptibles in contact with primary case=secondary attack rate
basic reproductive rate= AVERAGE numberof successful trainsmission per infected person (secondary attack rate but applied to the general pop)

Question 14

What does R0 have to be for infection to persist

Answer 14

more than 1

Question 15

What happens to R0 when immunity is introduced into a pop

Answer 15

R0 should decrease and is termed Rn (net/effective)

Question 16

What equation links Rn and R0

Answer 16

Rn=Ro x s ( proportion of susceptible pop)

Question 17

If Rn=1 ie. 1/R0 what would happen if s is less than

Answer 17

incidence will decrease

Question 18

If RN=1 what would happen is s is more than

Answer 18

incidence will increase

Question 19

What is the Herd immunity threshold

Answer 19

the proportion of population that needs to be immune for the infection to be stable
HIT =Rn-1/R0

Question 20

How can HIT be used to eradicate an infection

Answer 20

Proportion of immunsed pop must exceed the threshold