Lecture 36: Outbreaks Flashcards
What is the concept of one health?
Focusing on all aspects of health, animals, environment - not just human
What 6 factors influence the spread of disease?
- Properties of the agent
- Sources of infection
- Biological reservoirs
- Host factors
- Exposure variation
- Environment
What factors are included in an epidemiological triangle?
What (agent)
Who (person/population)
Where (place)
When(time)
Why/how (causes, risk factors & modes of transmission)
Note: angus make sure you learn the triangle - slide 6
Give 5 examples of infectious agents:
Bacteria, viruses, fungi, protozoa, helminths (parasitic worms)
What is an infection?
Entry of a microbiological agent into a higher order host and its multiplication within the host
What is an infestation?
An infection that only includes the external surface e.g. lice and scabies
What is infectivity?
Ability of an organism to invade and multiply in a host (secondary attack rate)
What is 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 (case-fatality rate)
What is direct transmission?
Touching or inhaling infectious secretions (saliva, respiratory droplets, urine, faeces, other body fluids)
What is indirect transmission?
Always involves a vehicle:
- Inanimate = fomites (bedding, clothes, utensils), food or water, soil
- Live = vector (mosquitos, ticks)
What is airborne transmission?
Droplet nuclei = small particles <5μm e.g. tuberculosis
Describe the infectious process:
- Infection - latent
- Incubation period - latent to infectious period
- Clinical disease - infectious period
- Recovery - ends with being immune
What is an outbreak/epidemic?
Unexpected increase in the incidence of a disease within a large population
- Occurrence of cases in excess of those expected
- Two or more cases identified from a common source
- Epidemic limited to a localised increase in the incidence of disease
- Epidemic arising in an area that had no cases for a long time
Describe an endemic and name the two types of an endemic:
Constant presence of a disease or infectious agent within a geographical area or population group
E.g. malaria is endemic to parts of Africa and Asia
2 types:
Holoendemic and Hyperendemic
What is a Hyperendemic?
Intense disease with time periods of no transmission e.g. during the dry season - persistent disease with all ages infected
What is a Holoendemic?
Intense disease all year round - children mainly infected, most adults immune
What is a pandemic?
Disease affects a large number of people and crosses many international boundaries
What are clusters of disease?
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
- May have a suspected environmental cause
What is generation 1 of a disease?
There is a primary (initial) case within a population with no immunity to a specific disease
What is a secondary attack rate?
Transmission or spread from initial case
What is generation 2 of a disease?
The number of people within the population who are infected from the initial case
This can continue for many generations until more people become immune so the rate of disease spread decreases
Who recognises an outbreak?
- Members of the community
- Media
- Clinicians
- Local public health agencies
- National public health agencies
- Academic organisations
Why do outbreaks need to be investigated?
- To stop and prevent further illness
- To prevent further outbreaks from other similar sources
- To address public concerns and involve the public in disease control
- To reduce direct and indirect costs
- To identify new mechanisms of transmission of known diseases
- To identify new or emerging disease agents
What are the outbreak investigation steps?
- Preparation
- Surveillance
- Confirmation
- Outbreak description
- Outbreak investigation
- Analytic epidemiology component
- Environmental component
- Laboratory component - Outbreak control
- Outbreak communication
- Outbreak documentation
What is outbreak confirmation?
Ensuring that the increase in disease isn’t due to seasonal effects
What is included in an outbreak description?
- Person - who
- Place - where
- Time – when
Describe the 3 different types of outbreaks:
- Common source
- Point source e.g. common event such as contaminated food at the event
- Continuous common source e.g. contaminated water supply in community
- Intermittent source e.g. fine water supply sometimes but not other times - Propagated source (person to person)
- Household/institutional - Mixed
- Point source then propagated person to person
What are the features of an epidemic curve?
Cases (y) over generation (x)
Follows a fairly normal distribution - cases increase and as the peak the cases start to decrease
What information can an epidemic curve provide outbreak investigators?
- Incubation period – the time from exposure to onset of symptoms
- Distribution of cases over time, which will help determine whether transmission is person-to-person or point-source.
What is the plan for pandemics?
- Plan for it
- Keep it out – border control, preparation, communication, surveillance, self-isolation
- Stamp it out – early recognition, case finding, contact tracing & isolation
- Manage it – delay the increase – infection control, triage, treatment, closure of institutions…bracing the health system & the public
- Recover from it
What is the difference between a point source outbreak and a propagated (person-to-person) outbreak?
A point-source/common-source outbreak occurs when many people are suddenly exposed to the same source of infection, such as a contaminated water supply or contaminated food at an event. In contrast, a propagated outbreak occurs when an infection is introduced to a susceptible population with subsequent transmission from person to person and a progressive increase in incidence.
