9. Infection Prevention

Question 1

Describe the communicable nature of infections

Answer 1

•Many infections are transmissible
- From a non-human source to humans
- From person to person
•Directly
•Indirectly

Question 2

What is a common source in terms of infection?

Answer 2

A common source outbreak is one in which a group of persons are all exposed to an infectious agent or toxin from the same source.

Question 3

What are examples of common sources of infection?

Answer 3

• environmental: e.g. legionella pneumophilia
• food/ water e.g. food poisoning organisms - onward transmission possible
• animals e.g. rabies - onward transmission possible
• some pathogens can then be passed on from human to human

Question 4

What are examples of infections that are passed on directly person to person?

Answer 4

Influenza, norovirus, neisseria gonorrhoea

Question 5

What are examples of vectors?

Answer 5

Mosquitos

Question 6

Define endemic disease

Answer 6

The usual background rate

Question 7

Define outbreak

Answer 7

Two or more cases linked in time and place

Question 8

Define epidemic

Answer 8

A rate of infection greater than the usual background rate

Question 9

Define pandemic

Answer 9

Very high rate of infection spreading across many regions, countries, continents - global

Question 10

What is the basic reproduction number?

Answer 10

R0 - the average number of cases one case generates over the course of its infectious period, in an otherwise uninfected, non immune population

Question 11

What does it mean if R0 > 1 ?

Answer 11

Increase in cases

Question 12

What does it mean if R0 = 1 ?

Answer 12

Stable number of cases

Question 13

What does it mean if R0 < 1 ?

Answer 13

Decrease in cases - disease will die out as for every one case, there is less than one secondary case

Question 14

What are examples of diseases with high basic reproduction numbers?

Answer 14

Measles, pertussis, diphtheria

Question 15

What are causes for outbreaks, epidemics and pandemics?

Answer 15

1. New pathogens - antigens, virulence factors, antibacterial resistance
2. New hosts - non-immunes e.g. babies and young children
3. New practice - social, healthcare
4. place

Question 16

Define infectious dose

Answer 16

a minimum number of microbes required for an infection to proceed

Question 17

Compare person-to-person direct and indirect transmission

Answer 17

These pathogens are entirely person to person there are no animals or environmental factors involved.
Examples include influenza, norovirus and neisseria gonnorhoea.

In indirect transmission a vector is important e.g in the transmission of malaria from person to person using mosquitoes

Question 18

What is an example of a micro-organism with a low infectious dose?

Answer 18

E Coli —> does not take many to cause infection - only 1 cyst can cause infection

Question 19

Give two examples of micro-organisms with a high infectious dose?

Answer 19

Salmonella, cholera

Question 20

What is the epidemic curve?

Answer 20

As the outbreak grows amongst susceptible people, number of infected people increase

Then as people recover, less susceptible people to infection so number of infected people decrease

Question 21

What is the nature of small scale outbreaks?

Answer 21

Tend to have a stochastic nature

Question 22

How can we intervene with pathogens and vectors?

Answer 22

• reduce/ eradicate pathogen - antibacterials/ disinfectants, decontamination, sterilisation
• reduce/ eradicate vector - eliminate vector breeding sites

Question 23

How can we intervene with patients?

Answer 23

• improved health - nutrition, housing, medical treatment
• immunity - passive e.g. maternal antibody, IV immunoglobulin, active e.g. vaccination
• herd immunity

Question 24

What is herd immunity?

Answer 24

When a majority of a population are vaccinated against a disease. This means that even people who have not been vaccinated are less likely to get it because there are fewer people to catch it from.

Question 25

How can we intervene with practices?

Answer 25

• avoidance of pathogen or its vector: avoiding certain geographical regions, protective clothing and equipment e.g. netting, chemicals, long clothes, personal protective equipment in hospitals e.g. gowns, gloves, masks
• behavioural: safe sex, safe disposal of needles and not sharing them, food and drink preparation before travelling

Question 26

How can we intervene with places?

Answer 26

Environmental enginering: safe water, air, good quality housing, well designed healthcare facilities

Question 27

What are good consequences of control?

Answer 27

• decreased incidence or elimination of disease/ organism

E.g. smallpox, polio, dracunculiasis

Question 28

What are bad consequences of control?

Answer 28

• decreasing exposure to pathogen means less people must fight the infection
• decreases immune stimulus leads to decreased amount of antibody production amongst population
• increases amount of people protected against future outbreaks so increased susceptibles
• leads to later average age of exposure - increased severity of disease
  E.g. polio, hep A, chicken pox, congenital rubella syndrome