10. Preventing Infections

Question 1

Give 3 non-human sources of infection, and an example of an infection for each

Answer 1

Environmental eg Legionella pneumophila
Food/water eg food poisoning
Animals eg rabies

Question 2

Give 3 examples of infections that are spread by direct person-to-person contact

Answer 2

Influenza
Norovirus
Neisseria gonorrhoea

Question 3

Give an example of a way that infections can be spread person-to-person indirectly and give an example of an infection

Answer 3

Vector - mosquitos with malaria

Question 4

What is endemic disease?

Answer 4

The usual background rate

Question 5

What is an outbreak of a disease?

Answer 5

Two or more cases linked in time and place

Question 6

What is an epidemic of a disease?

Answer 6

A rate of infection greater than the usual background rate

Question 7

What is a pandemic of a disease?

Answer 7

A very high rate of infection spreading across manly regions, countries, continents

Question 8

What is R0?

Answer 8

The average number of cases one case generates over the course of its infectious period, in an otherwise uninflected, non-immune population

Question 9

What is happening if R0>1?

Answer 9

Increase in cases of the disease

Question 10

What is happening if R0=1?

Answer 10

There is a stable number of cases

Question 11

What is happening if R0<1?

Answer 11

Decrease in the number of cases of the disease

Question 12

Give 3 reasons for new outbreaks, epidemics or pandemics?

Answer 12

New pathogen
New hosts
New practice

Question 13

What is the infectious dose? What does it vary by?

Answer 13

Number of micro-organisms required to cause infection.

Varies by microorganism, presentation of microorganism, immunity of potential host

Question 14

Give an example of a bacteria with a large infectious dose, and one with a small infectious dose

Answer 14

Large - salmonella

Small - E. coli

Question 15

What shape are epidemic curves normally?

Answer 15

Bell-shaped

Question 16

What shape are small scale outbreak curves normally?

Answer 16

Stochastic nature (random)

Question 17

Give 2 examples of interventions that reduce/eradicate pathogens and vecotors

Answer 17

Sterilisation

Eliminate vector breeding sites

Question 18

Give 2 examples of interventions that reduce patient susceptibility to infection

Answer 18

Improved health eg nutrition

Improved immunity eg active via vaccination

Question 19

What is herd immunity?

Answer 19

Vaccinating a proportion of the population protects individuals, that are not vaccinated, from infection

Question 20

What two things can affect how many people you need to vaccinate in herd immunity?

Answer 20

How infective pathogen is

If you vaccinate super-spreaders

Question 21

Give 2 examples of interventions related to practice and preventing infection spread

Answer 21

PPE in hospitals

Safe sex - condoms

Question 22

Give 2 examples of interventions against the spread of disease related to the place/environment

Answer 22

Safe water

Well designed healthcare facilities

Question 23

What are some bad consequences of trying to control the spread of infectious diseases?

Answer 23

Decreased exposure to pathogen, so decreased immune stimulus, decreased antibody, increased number of susceptible, leading to outbreak.
Later average age of exposure leads to increased severity eg chicken pox, polio (more likely to cause neurological damage)

Question 24

What two things does surveillance of infectious diseases involve?

Answer 24

What is happening now, and what might happen int he future

Question 25

What happens in an acute viral infection?

Answer 25

Multiple rounds of replication, which results in the death of the host cell. Large amounts of virus in tissues for a short space of time. Eg influenza virus

Question 26

What happens in a latent viral infection?

Answer 26

Caused by DNA viruses or retroviruses. Persistence of viral DNA as an extrachromosomal element or as in integrated sequence within the host genome (retrovirus). Reactivation occurs, and some retroviruses may result in transformation of the cell which leads to cancer

Question 27

What happens in chronic viral infection?

Answer 27

Virus particles continue to be shed after the period of acute illness. Release of virus particles without death of the host cell or overt cellular injury. Usually caused by RNA viruses. Amount of virus produced is less than in acute infections. Viruses often mutated from original. Associated with defective host immune responses that are insufficient to clear the infection.