Definitions

Question 1

Basic reproduction number (R0)

Answer 1

Avg # secondary infectious persons resulting from 1 infectious person following their introduction into a totally susceptible population.

Question 2

Beta

Answer 2

The rate at which two specific individuals come into effect contact per unit time. (Technically per capita rate)

AKA: transmission coefficient, transmission rate, contact parameter.

Question 3

Carrier

Answer 3

Person who sheds infectious agent but does not have clinical symptoms.

Question 4

Case

Answer 4

Person who has clinical symptoms of an infection. (Not all cases are infectious)

Question 5

Catalytic model

Answer 5

Model typically used to describe data on prevalence of previous infection at age ‘a’ (z(a)), where lambda is the force of infection

Question 6

Closed population model

Answer 6

Model where assumed that there is no migration into or out of the population and no births/deaths.

Question 7

Compartmental model

Answer 7

Model where individuals in pop. are subdivided into broad subgroups (compartments) and model tracks individuals collectively.

Question 8

Density dependence assumption

Answer 8

Risk of infection increases as the population size increases.

AKA: ‘pseudo mass action’ assumption

Question 9

Deterministic model

Answer 9

Model which describes what happens on avg in a pop. but does not incorporate effects of chance.

Question 10

Doubling time (of an epidemic)

Answer 10

Time taken for number of infected individuals to double.

Question 11

Dynamic model

Answer 11

Model which describes changes in given quantities over time. Freq used to describe models which describe contact between individuals and so changes in prevalence of infectious fed back into changes in force of infection.

Question 12

Effective contact

Answer 12

Sufficient contact to lead to transmission if it occurs between infectious and susceptible person.

Question 13

Vaccine efficacy

Answer 13

Direct protection provided by infection (or other outcome). Excludes indirect (herd) effect.

Question 14

Vaccine effectiveness

Answer 14

Reduction in incidence of infection (or other outcome) in pop. resulting from combined effect of direct + indirect effect of vaccination.

Question 15

Eigenvalue(s)

Answer 15

Value which are intrinsic property of a matrix so that when a matrix is multiplied by some vector the result is some factor (eigenvalue) multiplied by that vector.

AKA: characteristic values

Question 16

Elimination

Answer 16

Reduction in incidence of an infection to very low levels with precise criteria being disease-specific.

Question 17

Endemic infection

Answer 17

An infection that is present in a pop. at a similar level over prolonged period.

Question 18

Epidemic

Answer 18

The increase and subsequent decrease in incidence following (re)introduction of an infection in a population. Also occurrence of cases in given locality which greatly exceeds that expected.

Question 19

Epidemic threshold

Answer 19

Min. prop. of pop. that needs to be susceptible for infection incidence to increase (1/R0)

Question 20

Eradication

Answer 20

Reduction in incidence of infection to zero.

Question 21

Force of infection

Answer 21

Rate at which susceptible individuals become infected per unit time.

AKA: incidence rate, hazard rate

Question 22

Frequency dependence assumption

Answer 22

Assumption that risk of infection remains unchanged as pop. size increases.

AKA: ‘true mass action’ assumption