Lecture 3- Communicable disease control Flashcards Preview

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Flashcards in Lecture 3- Communicable disease control Deck (36)
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1

Main ways in which people and animals catch and spread disease?

  • droplet spread
  • faecal-oral
  • direct contact
  • vector borne
  • blood borne
  • fomites

2

Droplet spread

Covid 19, flu, measles, meningococcal infection

3

Faecal-oral

 

Typhoid, E.coli, hepatitis A

4

Direct contact

 

Scabies, impetigo, HSV, STis

5

Vector borne

 

Malaria, dengue, lyme disease, leptospirosis, rabies

6

Blood borne

HIV, hepatitis B and C

7

Fomites

Non-living object that transmits disease causing pathogens e.g. door handle

8

The epidemiological triangle

9

Chain of infection

10

example of chain of infection

11

12

Source-Pathway-Receptor

 

Remove any one or block the route... interrupt transmission.

13

Measures to prevent further cases

  • Kill or inactivate the agent or the source

  • Antibiotics
  • Decontamination
  • Disinfection
  • Sterilisation
  • Heat treatment

14

Measures to prevent further cases

  • Interrupt the pathway of transmission

  • Isolation
  • Environmental hygiene
  • Personal hygiene
  • Personal protective equipment (PPE)

15

Measures to prevent further cases

  • Protect the host i.e. the receptor

  • Isolation
  • Immunisation
    • Of the vulnerable
    • Of the contacts
    • Cocoon
  • Chemoprophylaxis

16

For infection transmission to occur you need an…

 

  • Infectious agent (e.g. a virus or bacterium)…
  • A source of infection (an infectious person or contaminated water
  • An environment which enables infection to spread (an available pathway for infection such as shared space or poor sanitation) …..
  • A population with susceptible people in it (e.g. unvaccinated children exposed to measles

17

What happens if you cant control transmission of a disease? An

outbreak

18

What is an outbreak?

 

  • Two or more LINKED cases of an infection
    • (Linked in TIME, PLACE or PERSON)
  • An increase in cases of a disease OVER AND ABOVE the normal background rate of that disease
  • Any case of an infection that doesn’t normally occur in a setting and which carries a high risk to public health e.g. Ebola, Anthrax

19

A cluster?

 

  • An observed (real or perceived) aggregation of cases grouped in a single time period or setting and suspected to be above the expected level (CDC)
    • Not necessarily a proven link between cases (yet)
    • On investigation, may not actually even represent a significant rise in cases (play of chance leads to appearance of cluster)
    • Needs investigation as may lead to discovery of an outbreak
  • May need intervention to prevent an outbreak from occurring e.g. in Wuhan

20

epidemic curves

  • point source outbreak
  • extended outbreak
  • propagated outbreak

21

point source outbreak

e.g. food poisoning at a party - discrete

22

Extended outbreak e.g. contaminated water source

23

Propagated outbreak e.g. Covid 19

24

R0=

basic reproduction number of the virus

How many secondary cases each primary case produces assuming perfect conditions for pathogen e.g. 100% susceptible host

25

An infectious disease has a basic reproduction number (R0) of 8. 25% of the population are immune to the disease.

Which of the following statements describes the effective reproduction number of this disease?

a)  2

b)  4

c)  6

d)  8

e)  32

6

26

superspreaders

27

Aims of outbreak management

  • Minimise number of Primary Cases
  • Minimise number of Secondary Cases
  • Identify and eliminate continuing hazards (sources of infection)
  • Introduce measures to prevent future outbreaks

28

How do you know you have an outbreak in the first place?

Surveillance

 

e.g. Notifiable disease processes

  • for a number of listed infections, if you come across a case you must tell your local infection control team
  • E.g. meningococcal meningitis, ebola (high consequence disease), MMR, polio

29

investigating an outbreak process

Sequential

  1. Establish a case definition
  2. Confirm cases are real
  3. Determine background rate- is this really an outbreak
  4. Case Finding
  5. Describe cases in time, place and person
  6. Plot the epidemic curve
  7. Generate a hypothesis
  8. Test your hypothesis
  9. Generate conclusions

30

Case definition examples

 

 

 

  • Must be:
    • Precise
    • Accurate
    • Appropriately sensitive and specific
    • Appropriate for the available facilities
  • Should also enable you to characterise probable vs confirmed infection