Spread of Infection

Question 1

How can infection be transferred?

Answer 1

From non-human source to humans

From person to person– direct or indirect

Question 2

What are the different degrees of spread?

Answer 2

Source and infect one person then each person infects another three people
– spread is amplified
Source infects one person then the chain stops
– dead end transmission

Question 3

What is endemic disease?

Answer 3

The usual background rate of infection

Question 4

Define outbreak

Answer 4

Two or more cases that are linked in place and time e.g. in a school or hospital

Question 5

Define pandemic

Answer 5

Very high rate of infection that spreads across many regions, countries and continents

Question 6

What is the basic reproduction number?

Answer 6

The number of secondary cases that arise form each individual case in its infective period in a non-immune population
Is known as Ro

Question 7

What happens when Ro is greater than 1?

Answer 7

There is an increase in the number of cases

Question 8

What happens when Ro is 0?

Answer 8

There is a stable number of cases

Question 9

What happens when Ro is less than 1?

Answer 9

There is a decrease in the number of cases

Question 10

What is a characteristic of infections which have been eradicated or controlled?

Answer 10

Has a high basic reproduction number (BRN)

Question 11

What is the BRN of infections that are present at the moment?

Answer 11

2-5

Question 12

What are the reasons for outbreaks, pandemics and epidemics?

Answer 12

New pathogen has emerged
New host
New practice

Question 13

Describe reasons why outbreaks occur due to a new pathogen

Answer 13

Infection has different antigens

Infection has new virulence factorsInfection has developed antibiotic resistance

Question 14

Describe reasons why outbreaks occur due to a new host

Answer 14

People who are being infected are not immune

Person is entering an environment where they have not encountered a certain pathogen

Question 15

Describe reasons why outbreaks occur due to a new practice

Answer 15

Practice brings pathogen and patient together for the first time
Person is undertaking new practices

Question 16

Define the infectious dose

Answer 16

The number of micro-organisms required to cause infection.

Question 17

What does the infectious dose depend on?

Answer 17

Micro-organism
Characteristics of microorganism
Immunity of potential host

Question 18

What is an epidemic curve?

Answer 18

Shows the number of people who have been infected at any time interval

Question 19

What are small scale outbreaks?

Answer 19

Can have random outbreaks which do not necessarily follow a linear curve

Question 20

Give some interventions involving the pathogen to limit transmission

Answer 20

Reduce/eradicate pathogen 
- antibacterials
- decontamination
- equipment and air sterilisation
Reduce/eradicate the vector

Question 21

Give some interventions involving the patient to limit transmission

Answer 21

Improve health
Immunity
- passive
- active

Question 22

Define herd immunity

Answer 22

Need to vaccinate 90-95% of the population to have enough coverage to limit the spread of highly infectious disease

Question 23

Give some interventions involving practice to limit transmission

Answer 23

Avoid pathogen and vector
- protective clothing/equipment
Behaviour
- safe sex
- safe disposal of sharps
- food and drink preparation

Question 24

Give some interventions involving place to limit transmission

Answer 24

Environmental engineering

• safe water and air
• good quality housing
• well designed healthcare facilities

Question 25

What are the main consequences of good control of transmission?

Answer 25

1. Decreased incidence or elimination of disease and organism
2. Decreased immune stimulus to pathogen– decreased antibodies and increases susceptibilities
3. Later average age of exposure can increase severity of illness e.g. chickenpox, polio, congenital rubella