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Flashcards in Outbreak Investigation Deck (21):

Reasons to investigate an outbreak

1) Halt outbreak
2) Identify source of outbreak
3) Develop strategies to prevent similar outbreaks in the future
4) Evaluate existing prevention strategies
5) Describe new diseases
6) Address public concern
7) Fulfill international and national obligations


Main steps in outbreak investigation

1) Preparation
2) Surveillance
---Outbreak investigation---
3) Outbreak confirmation and assessment
4) Outbreak description
5) Full investigation (epi, environment, lab)
---Outbreak response----
6) Outbreak control
7) Communication
8) Documentation


What is the aim of preparation and what does it involve

Aim - ensure optimal preparedness
-Development of organisation outbreak plan that defines roles and responsibilities
- Maintain capacity and staff training, including cultural competence


What is the aim of outbreak 'surveillance' and what does it involve in NZ?

Aim - consistent and comprehensive collection and review of information of disease with outbreak potential
- Formal: Reading/reviewing EpiSurv, EARS
- Information: self-reports or alert from public


What are the steps involved with confirmation and assessment of an outbreak?

1) Confirm diagnosis
2) Confirm increase in cases is real
3) Confirm that the increase represents an outbreak
4) Decide what kind of outbreak it is
5) Decide on further investigation and control


How do you confirm a diagnosis and confirm that increase in cases is real?

-Rule out lab error and ensure that accurately diagnosed/meets case definition
- Has there been a change in lab tests? Or an increase in testing due to new clinicians? Or changes to reporting? (Artificial increases)


What else might account for an increase in cases other than an outbreak?

Increase in population size
Change in demographics (ie an increase in people at risk of the disease
Random variation
Increase in risk behaviour (eg BBQ in summer)
-> Compare observed with expected


What are 4 types of outbreak

Common event
Common site
Dispersed common source
Person-to-person/community wide


What is a common event outbreak

Exposure to a noxious influence at an event. Exposure is brief and essentially simultaneous and all resultant
cases develop within one incubation period of the disease. Cases have exposures that occur at
virtually the same place and time. Eg wedding, sports event, hui etc


What is a common site outbreak?

Exposure to a common noxious source, but at different times. eg Swimming pool, farm, restaurant


What is a dispersed common source outbreak?

A common noxious source that has been dispersed, so may have different sites and time. Eg hep a frozen blueberries


What is person-to-person/community wide outbreak?

An outbreak affecting individuals in a community, where transmission predominantly occurs by
direct exposure of susceptible people to infectious people. Usually a slow progressive increase in cases. eg hep a in immigrants in AKL


Once you have confirmed and assessed an outbreak how would you decide whether to investigate further

There is a need to rationalise resources, so not every outbreak will undergo full investigation. A decision is made based on what is know about the disease agent, source of illness and means of transmission (the more unknowns the more likely to investigate). Identification and verification may be all that is required for control (eg pertussis)


What are the steps of outbreak description?

1) Case definition
2) Case finding + info
3) Descriptive epi + epi curve
4) Review type of outbreak


When would you need to undertake a full outbreak investigation?

More important for common source outbreak. Generally not needed for primarily person to person as focus on control, exception: sometimes want to case find the primary case (very first case) in case still infectious and capable of spreading e.g. TB


What are the components of a full investigation

Analytic Epi
Lab component


What are the types of analytic epi you might undertake?

Case control - useful when cases have been identified but population at risk is unclear (eg dispersed, common site) Explore exposure history
Retrospective cohort: useful when time frame is short eg common event and where total pop at risk can be defined (eg wedding). Compare disease risk amongst two populations characterised by their exposure. Can calculate attack rate.


What is an environmental investigation?

May involve site visit. Work through the system to see where the systematic break down occured eg failures in food prep, water treatment, cold chain.


What is lab component of full investigation?

Identifying organisms and toxins for confirming link between suspected cases and substances


What are the steps of outbreak response



What are the steps of outbreak control

Depends on the source, but the key factors are:
1) Outbreak source - close food premesis, treat cases/carriers
2) Contaminated vehicles of tranmission: recall products, boil water
3) Management of susceptible humans: education to food handlers, physical barriers (Eg condoms)