L9: Infection prevention

Question 1

How are infections transmitted?

Answer 1

Non-human source to human source
Humans to other humans
- Directly
- Indirectly via vector

Question 2

Where do infections come from? What are some examples?

Answer 2

Usually a common source

• Environment –> Legionella pneumophila
• Water/ food–> Food poisoning
• Animals–> rabies

Question 3

What are some examples of direct human transmission?

Answer 3

Influenza
Norovirus
Neisseria gonorrhoea

Question 4

What is an example of indirect human transmission?

Answer 4

Malaria via mosquitos

Question 5

Define endemic?

Answer 5

Usual background rate of infection

Question 6

Define outbreak?

Answer 6

Two or more cases linked in time and place

Question 7

Define epidemic?

Answer 7

Rate of infection greater than usual rate considering the season
e.g. flu greater in winter than summer, not referred to as an epidemic

Question 8

Define pandemic?

Answer 8

Very high rate of infection spreading across many regions, countries and continents
Usually a novel agent, no one immune to it (no vaccination etc…)
Everyone susceptible

Question 9

What is the basic reproduction number?

Answer 9

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

Question 10

What does R0 > 1, R0 = 1 and R0 < 1 mean?

Answer 10

R0 > 1 increase in number of cases, number of cases will grow
R0 = 1 means stable number of cases, stable endemic conditions
R0 < 1 decrease in number of cases, number of cases will die out

Question 11

What are the reasons for outbreaks, epidemics and pandemics?

Answer 11

New pathogen (pathogen)
New host (patient)
New practice (practice)

Question 12

What do we mean by new pathogen?

Answer 12

Noval agents
Old agent but dressed up/ coated in different way
–> antigenic- new antigens on it

Question 13

What do we mean by new host?

Answer 13

Immune naive people–> without the correct antibodies
New borns–> antibody transfer from mother in last few weeks of gestation–> after 3 months antibodies disappear–> replaced when baby expose to pathogen
–> outbreaks in nursery’s
New places–> exposed to different factors when we go to new places

Question 14

What do we mean by new practice?

Answer 14

Social practices and healthcare

Tattoos, feeding cattle brain to cattle

Question 15

What factors determine tranmissibility?

Answer 15

Way it is spread–> direct contact, areosol, muscosal membrane interaction etc
Size of dose required–> how infectious are they? how much of the organism is needed? Varies a lot
Depends on immunity

Question 16

What do epidemic curves show?

Answer 16

Number of people infected at each time interval over a period of time can be days, weeks, years etc…

Question 17

Why does it decline?

Answer 17

Either people become immune to the pathogen so less of population affected
OR
People die so there is less of the population to be infected

Question 18

What model does the epidemic curve form?

Answer 18

SIR models
Susceptible 
Infected 
Recover
Lots of pathogens follow this model, you are susceptible until you have had it then you recover
e.g. measles vaccinations

Question 19

What happens with something such as norovirus?

Answer 19

Peaks over the winter months

Disappears over the summer months

Question 20

What happens in a smaller poplulation?

Answer 20

Not as predictable, doesn’t follow the epidemic curve
Varying features of outbreaks in smaller population
Stochastic nature–> lots of mini epidemic curves that can overlap or may not overlap
Difficult/ Be careful when interpreting results outcome may/may not be due to intervention

Question 21

What interventions can we do at pathogen level?

Answer 21

Reduce/ eradicate pathogen
–> Antibacterials including disinfectants
–> Decontamination –> sewage and water separate
–> Sterilisation
Reduce/eradicate vectors
–> Eliminate vector breeding sites

Question 22

What interventions can we do at patient level?

Answer 22

Improve health –> good healthy, well housed well nutritioned population
- nutrition
- medial treatment
Immunity
- Passive –> maternal antibody, intravenous immunoglobulins–> premature children risk of Respiratory syncytial virus (RSV) given monoclonal antibodies–> protection - children normally get it before the age of two
- Active –> vacciniations

Question 23

Why do vaccination in large populations work?

Answer 23

Herd immunity
Reduced the risk if infection for those unable to have vaccine
Vaccinated people in contact with infected person do not get infected
Vaccinate proportion of population prevents spread

Question 24

What intervention can we do at practice and place level to reduce infection?

Answer 24

Avoid pathogen/ vector
–> Associated with geographical region–> don’t go
–> Protective clothing/ equipment (long sleeves , trousers protect against mosquito etc)
–> Personal protective equipment in hosptials
Behaviour
–> safe sex (reduce HIV infection risk)
–> safe disposal of sharps
–> Food and drink preparation–> cooked properly, precautions when abroad etc

Place
Environmental engineering
--> Safe water
--> Safe air 
--> Good quality housing 
--> Well designed healthcare facilities

Question 25

What are the benefits of control?

Answer 25

Decreased incidence or elimination of disease/ organism e.g. smallpox, polio, drancunculitis

Question 26

What are the negative effects of control?

Answer 26

Reduced exposure–> decreased immune stimulus–> decreased antibody–> increased susceptibles–> outbreak
Vaccination–> increased number of neonates with severe illness because didn’t get antibodies from mother–> vaccinated agaist whooping cough now
Exposure at later average age–> more severe effect

Question 27

What do we mean by survillance?

Answer 27

What is happening now, here and elsewhere?

What might happen?