Lecture 36: Outbreaks, Epidemics and Clusters Flashcards
How many stages are there that describe the epidemiological transition (changing pattern of disease)?
5
Describe the epidemiological transition
The birth rate and death rate are high and the total population is low and then the death rate falls so population begins to increase and then birth rate falls and the total population keeps increasing and then plateaus
What happens in stage one of the epidemiological transition?
birth rate and death rate are high
What happens in stage 5 of the epidemiological transition?
birth rate is very low and death rate is low
Where do high and low income countries sit in terms of stages on the epidemiological transition? Why is this?
High income countries are at level 5 because there is improved living conditions and low income countries are at level 1 due to infectious diseases and newborn and maternal problems due to inadequate care
What does vector-borne mean?
infections coming from mosquitos
What does zoonotic mean?
infections coming from other animals
What are infections coming from other animals called?
zoonotic
What is one health?
The interaction between human, animals and the environment and how we can work better with agriculturalists, vets, climate change people to improve health
What 6 things influence the spread of disease?
- ______ of the agent
- _______ of infection
- biological _______
- ________ factors
- ________ variation
- ________
- properties of the agent
- sources of infection
- biological reservoirs
- host factors
- exposure variation
- environment
One of the things that influences the spread of disease is the properties of the agent. What is meant by this?
how virulent it is, how it is transmitted, does it mutate
One of the things that influences the spread of disease is the sources of infection. What is meant by this?
where does it come from - does it come from soil, water, insects, animals
One of the things that influences the spread of disease is biological reservoirs. What is meant by this?
can it be present in an animal that don’t get infected, they just pass it on?
One of the things that influences the spread of disease is host factors. What is meant by this?
is the host immunosuppressed, are they malnourished, or really healthy
One of the things that influences the spread of disease is exposure variation. What is meant by this?
are people contracting the disease in a closed environment like a plane? it will spread faster if it is
One of the things that influences the spread of disease is the environment. What is meant by this?
has climate change impacted the environment ie. is it warmer so mosquitos are more likely to be present
What three things contribute to the epidemiological triangle and what three things do these make up?
- the host
- the agent
- the environment
- the host and the agent make up the transmission part of the triangle
- the agent and the environment make up the survival part of the triangle
- the host and the environment make up the immunity part of the triangle
What is meant by the “host” in the epidemiological triangle?
descriptive epidemiology - describing data
What is meant by the “agent” in the epidemiological triangle?
laboratory investigation - determining what the agent is
What is meant by the “environment” in the epidemiological triangle?
environmental investigation into what caused the disease eg. rainfall
What can we learn from the epidemiological triangle?
- what (agent)
- who (person/population)
- where (place)
- when (time)
- why/how (causes, risk factors and modes of transmission)
What are some examples of infectious agents?
bacteria viruses fungi protozoa helminths (parasitic worms)
Define infection
entry of a microbiological agent into a higher order host and its multiplication within the host
Define infestation and give an example
multiplication of a microbial agent on (only) the surface of a higher order host and multiplication eg. lice
Define infectivity
the ability of an organism to invade and multiply in a host - defines the secondary attack rate
Define pathogenicity
the ability of an organism to produce clinical symptoms and illness - defines the proportion of those exposed who get ill
Define virulence
the ability of an organism to produce serious disease - defines the case-fatality rate
What are the three modes of transmission?
- direct
- indirect
- airborne
What is meant by direct transmission of disease?
touching or inhaling infectious secretions such as saliva, respiratory droplets, urine, faeces, other body fluids
What is meant by indirect transmission of disease?
it always involves either another object which can either be inanimate such as bedding, clothes, utensils, food, water, soil; or live via a vector such as mosquitos or ticks
What is meant by airborne transmission of disease?
droplet nuclei travel in the air
What are the three parts to the infectious process?
- the incubation period
- the clinical period/the disease period
- the recovery period
What is meant by the latent part of the infectious process?
when you are infected but you can’t spread the disease
What is meant by the infectious period of the infectious process?
This is before the symptoms begin and it stops before you have recovered. This spans both the incubation period and the recovery period
When are you most infectious?
in the first few days after developing the disease
Define an outbreak/epidemic
An unexpected rise in the incidence of a disease - this can be limited to a localised increase in the incidence of disease or rising in an area that had no cases for a long time, This can also be defined as two or more cases identified from a common source or cases in excess of the expected number in a given time or place
Define endemic
the constant presence of a disease or infectious agent within a geographical area or population group
What are two types of endemic? Define them and state who is mainly affected
- holoendemic - intense diseases all year round, children mainly affected, most adults immune
- hyperendemic - intense disease with time periods of no transmission such as during the dry season, persistent diseases with all ages infected
Define pandemic
when a disease affects a large number of people and crosses many international boundaries
Infections are often reported in clusters. Define clusters
an aggregation of relatively uncommon events or disease in space and/or time that are though to be greater than could be expected by chance
What sort of diseases are usually reported as clusters?
rare non-infectious diseases such as HIV/AIDS
Define primary case
the first case
Define index case
the first case that is recognised by the health organisations
What is the secondary attack rate?
the transmission or spread from the initial case
Define R0
how many people will one person spread the disease to
Who recognises an outbreak? (6)
- members of the community
- media
- clinicians
- local public health agencies
- national public health agencies
- academic organisations
Why do we need to investigate outbreaks? (6)
- to ______ and ______ further illness
- to prevent further ________ from other similar _______
- to address _______ ______ and involve the _____ in disease _______
- to reduce _______ and _________ costs
- to identify new mechanisms of ________ of known ________
- to identify new or emerging _________ agents
- 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 8 outbreak investigation steps?
- preparation
- surveillance
- confirmation
- outbreak description
- outbreak investigation
- outbreak control
- outbreak communication
- outbreak documentation
What are three parts to the outbreak investigation?
- analytic epidemiology component
- environmental component
- laboratory component
What three things describe an outbreak?
the person (who), the place (where) and the time (when)
What are the three types of outbreaks?
- common source
- propagated source
- mixed
What are the three types of common source outbreaks? Give an example for each
- point source (eg. from a common event such as all the cases attended the same wedding
- continuous common source (eg. continually contaminated water supply)
- intermittent source (eg. only contaminated water supply after heavy rainfall)
Give an example of propagated source outbreaks
person to person such as within a household or institution
What is meant by mixed outbreaks?
point source then propagated person to person
What does an epidemic curve graph?
the number of cases of a disease over time
What does a common (point) source epidemic curve look like and why?
it is bell shaped because not everyone exposed at the same time gets unwell at the same time
What does a continuous) source epidemic curve look like and why?
constant high cases over time because the infectious disease is not identified and people and people continue to get sick
What does an intermittent source epidemic curve look like?
small groups of cases with blocks of no cases intermittently
What does a propagated source epidemic curve look like?
one case and then more cases and then lots of cases because one case spreads it to people who spread it to more people and then they spread it to more people
What is the plan for pandemics?
- plan for it
- keep it out
- stamp it out
- manage it
- recover from it
One of the steps to managing pandemics is to keep it out. What is meant by this?
border control, preparation, communication, surveillance, self-isolation
One of the steps to managing pandemics is to stamp it out. What is meant by this?
early recognition, case finding, contact tracing and isolation
One of the steps to managing pandemics is manage it. What is meant by this?
delay the increase by infection control, triage, treatment, closure of institutions, bracing the health system and the public
