Lecture 36 -Outbreaks Flashcards
What influences the spread of disease
- Properties of the agent
- Sources of infection
- Biological reservoirs
- Host factors
- Exposure variation
- Environment
Three elements of the epidiomological triangle
- Host - descriptive epidemiology
- Environment - Environmental investigation
- Agent - Laboratory investigation
Infectious agents
Bacteria, viruses, fungi, protozoa, parasitic worms
what is Infection
Entry of microbiological agent into a higher order host and its mutliplication within the host
- Infestation - external surface only e.g. lice or scabies
what is Infectivity
ability of an organism to invade and multiply in a host (secondary attack rate)
Pathogenicity
Ability of an organism to produce clinical symptoms and illness (proportion of those exposed who get ill)
What is virulence
Ability of an organism to produce serious disease
Transmission types
- Direct
- Indirect
- Airborne
Direct transmission
Touch or inhaling infectious secretions
Indirect transmission
Through a vehicle
- Inanimate - fomites (bedding, clothes)
- Live - vector (mosquitos)
Airborne transmission
Droplet nuclei smaller than 5 micrometer e.g tuberculosis
The infectious process
- Incubation period
- Clinical disease
- Recovery
- Latent - not able to spread
- Infectious period - spreading of the disease
what is Outbreak / epidemic
Unexpected increase in the incidence of a disease
- Occurencr of cases one excess of those expected
- Epidemic limited to a localised increase in the incidence of disease
- Epidemic arising in an area that had no cases for a long time
What is endemic
- Constant presence of a disease or infectious agent within a geographical area ir population group e.g. malaria is endemic
- Holoendemic
- Hyperendemic
Holoendemic
Intense disease all year round children mainly infected, most adults immune
Hyperendemic
Intense disease with time periods of no transmission e.g. during the dry season - persistent disease with all ages infected
What is pandemic
Disease affects a large number of people and crosses many international boundaries
What is a disease cluster
Aggregation of relatively uncommon events or diseases in space and/or in time that are thought to be greater than could be expected by chance
- Usually rare non-infectious diseases
Who recognises an outbreak
- Members of community
- Media
- Clinicians
- Local public health agencies
- National public health agencies
- Academic organisations
Key steps in outbreak investigation
- Preparation - ready to response
- Surveillance - looking at the numbers
- Confirmation
- Outbreak description - Person, place, time
- Outbreak investigation
1. Analytic
2. Environmental
3. Laboratory - Outbreak control
- Outbreak communication
- Outbreak documentation
Types of outbreaks
- Common source
- Point source e.g. common event
- Continuous common source - exposure begins and continues
- Intermittent source - propagated source (person to person)
- Mixed e.g. source then propagated
Why investigate outbreaks
- To stop further illness
- prevent further outbreaks
- Address public concerns
- Identify new disease agents or transmission mechanisms
The outbreak crytosporiodiosis - Surveillance, confirmation and description
- Early reports from social media - gastro possible link to drinking water
- Formal notification of one case 11 days after onset of symptoms
- More notifications of cases from hospital
Crypto - outbreak investigation
Analytic:
- We knew the causative agent but didn’t know where it came from
- Investigation of cases using an expanded questionnaire
- developed a case definitions; primary and secondary
Laboratory:
- samples sent to lab - detection
- Whole genome sequencing
Crypto - outbreak control
- Boil water notice - no new primary cases
- Environmental and lab investigation continued
Crypto geospatial mapping - Outbreak communication
- Distribution of cases was rapid and distributed
- Localised contamination event in distal reticulation
- Water contamination prior to the two mile water treatment
Crypto - outbreak outcome
- Crypto outbreak
- Likely environment contamination into the lake which was the source of the drinking water
- No protozoal barrier on the drinking water
- Boil water implementation stopped the outbreak
- Huge media and political interest
Planning for pandemic in NZ
- Plan for it
- keep it out - border control
- Stamp it out - early recognition
- Manage it - delay the increase
- Recover from it
