Lecture 3- Communicable disease control Flashcards
Main ways in which people and animals catch and spread disease?
- droplet spread
- faecal-oral
- direct contact
- vector borne
- blood borne
- fomites
Droplet spread
Covid 19, flu, measles, meningococcal infection
Faecal-oral
Typhoid, E.coli, hepatitis A
Direct contact
Scabies, impetigo, HSV, STis
Vector borne
Malaria, dengue, lyme disease, leptospirosis, rabies
Blood borne
HIV, hepatitis B and C
Fomites
Non-living object that transmits disease causing pathogens e.g. door handle
The epidemiological triangle
Chain of infection
example of chain of infection
Source-Pathway-Receptor
Remove any one or block the route… interrupt transmission.
Measures to prevent further cases
- Kill or inactivate the agent or the source
- Antibiotics
- Decontamination
- Disinfection
- Sterilisation
- Heat treatment
Measures to prevent further cases
- Interrupt the pathway of transmission
- Isolation
- Environmental hygiene
- Personal hygiene
- Personal protective equipment (PPE)
Measures to prevent further cases
- Protect the host i.e. the receptor
- Isolation
- Immunisation
- Of the vulnerable
- Of the contacts
- Cocoon
- Chemoprophylaxis
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
What happens if you cant control transmission of a disease? An
outbreak
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
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
epidemic curves
- point source outbreak
- extended outbreak
- propagated outbreak
point source outbreak
e.g. food poisoning at a party - discrete
Extended outbreak e.g. contaminated water source
Propagated outbreak e.g. Covid 19
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
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
superspreaders
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
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
investigating an outbreak process
Sequential
- Establish a case definition
- Confirm cases are real
- Determine background rate- is this really an outbreak
- Case Finding
- Describe cases in time, place and person
- Plot the epidemic curve
- Generate a hypothesis
- Test your hypothesis
- Generate conclusions
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
Example of case definition for measles
Finding your cases (and contacts)
- 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
Case control example
Once an association has been made…
Convene an Outbreak Control Team (outbreak management group, incident management team)
- Multidisciplinary team who work together to manage outbreaks
Statutory/legal frameworks
- Notifiable infections/agents
- Control of Disease Act
- Environmental Health Regulations
- International health regulations
When the outbreak is over
- Declare it over (no new cases within x2 incubation period)
- Debrief
- bContingency planning
