Lecture 3- Communicable disease control

Question 1

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

Answer 1

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

Question 2

Droplet spread

Answer 2

Covid 19, flu, measles, meningococcal infection

Question 3

Faecal-oral

Answer 3

Typhoid, E.coli, hepatitis A

Question 4

Direct contact

Answer 4

Scabies, impetigo, HSV, STis

Question 5

Vector borne

Answer 5

Malaria, dengue, lyme disease, leptospirosis, rabies

Question 6

Blood borne

Answer 6

HIV, hepatitis B and C

Question 7

Fomites ​

Answer 7

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

Question 8

The epidemiological triangle

Answer 8

Question 9

Chain of infection

Answer 9

Question 10

example of chain of infection

Answer 10

Question 12

Source-Pathway-Receptor

Answer 12

Remove any one or block the route… interrupt transmission.

Question 13

Measures to prevent further cases

• Kill or inactivate the agent or the source

Answer 13

• Antibiotics
• Decontamination
• Disinfection
• Sterilisation
• Heat treatment

Question 14

Measures to prevent further cases

• Interrupt the pathway of transmission

Answer 14

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

Question 15

Measures to prevent further cases

• Protect the host i.e. the receptor

Answer 15

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

Question 16

For infection transmission to occur you need an…

Answer 16

• 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

Question 17

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

Answer 17

outbreak

Question 18

What is an outbreak?

Answer 18

• 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

Question 19

A cluster?

Answer 19

• 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

Question 20

epidemic curves

Answer 20

• point source outbreak
• extended outbreak
• propagated outbreak

Question 21

Answer 21

point source outbreak

e.g. food poisoning at a party - discrete

Question 22

Answer 22

Extended outbreak e.g. contaminated water source

Question 23

Answer 23

Propagated outbreak e.g. Covid 19

Question 24

R0=

Answer 24

basic reproduction number of the virus

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

Question 25

An infectious disease has a basic reproduction number (R0) of 8. 25% of the population are immune to the disease. ## Footnote Which of the following statements describes the effective reproduction number of this disease? a) 2 b) 4 c) 6 d) 8 e) 32

Answer 25

6

Question 26

superspreaders

Question 27

**Aims of outbreak management**

Answer 27

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

Question 28

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

Answer 28

**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

Question 29

investigating an outbreak process

Answer 29

**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

Question 30

**Case definition examples**

Answer 30

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

Question 31

Example of case definition for measles

Answer 31

Question 32

**Finding your cases (and contacts)**

Answer 32

* Describe them in detail: * Demographics * Symptoms and TIMING * Travel/Other exposures including food * Immunisations * Ethnic/Cultural/Religious Background * Plot your epidemic curve * Formulate your hypothesis; what patterns have emerged? * Test it: Case-control study

Question 33

Case control example

Answer 33

Question 34

**Once an association has been made…**

Answer 34

**Convene an Outbreak Control Team (outbreak management group, incident management team)** * Multidisciplinary team who work together to manage outbreaks

Question 35

**Statutory/legal frameworks**

Answer 35

* Notifiable infections/agents * Control of Disease Act * Environmental Health Regulations * International health regulations

Question 36

**When the outbreak is over**

Answer 36

* Declare it over (no new cases within x2 incubation period) * Debrief * bContingency planning