Outbreak Investigations Flashcards by Bella Fal

What is an outbreak?

An unusual increase in the numner of cases of an illness for that time period of a specific geographical area

Based on Time, Place, Person

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Which diseases are considered an ‘outbreak’ with just one case?

Polio
Ebola

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What would the R number be in endemic areas of disease transmission?

R = 1 (roughly)

Epidemics occur in ENDEMIC areas when R >1

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How do you monitor Meningitis re: outbreaks?

You would expect that in a DRY SEASON in the MENINGITIS BELT there will be a number of cases. With meningitis you worry when cases reach a set threshold.

You have an ALERT THRESHOLD (time of public health interventions) and an EPIDEMIC THRESHOLD

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What is the definition of Cluster?

An aggregation of cases in a given area over particular period without regard to whether the number of cases is more than expected or whether cases are related

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What is the definition of Pandemic?

An epidemic that has a global reach, crossing international boundaries & affecting large numbers

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You have been asked to investigate a potential outbreak. What do you need to know about the disease/ what are the objectives of your outbreak investigation?

Confirm an epidemic
Identify the source & transmission modes
Identify the causal agent
Identify groups at risk
Develop strategies to prevent future epidemics
Evaluate existing strategies
Describe new diseases & learn more about known diseases

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How might your detect an outbreak?

Regular analysis of surveillance data
- e.g. Current Measles outbreak in Somalia
- e.g. Malaria outbreak in Uganda 2015
Alerts from immediately notifiable diseases
- Polio
- VHF (Ebola, Marburg)
Reports/Rumours/Suspicions of diease

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What is PHEIC?

Public Health Emergency of International Concern

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What are the 10 steps of an outbreak investigation?

Preparation
– Investigation
– Administration
– Consultation
Establish existence of outbreak
Verify diagnosis
Define & identify cases
– Construct working case definition (CD)
– Find systematically cases & record information
Perform descriptive epidemiology
– Time, place, person
Develop hypotheses
Evaluate & refine hypotheses
– studies (epi, lab, environmental)
Implement control & prevention measures
Initiate/reinforce surveillance activities
Communicate findings

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From the 10 steps of an outbreak investigations:

Step 1: Preparation

How do you prepare for an outbreak?

Review the literature, discuss with experts and assemble the materials required to monitor, diagnose, treat the disease

Manage the operational issues: Team members and stakeholders, Inter-agency co-ordination , Logistics (vehicles, radios

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From the 10 steps of an outbreak investigations:

Step 2: Establish the existence of an outbreak.

How do you do this?

? Is this a cluster or a true outbreak

Look at surveillance records, community surverys
Rule out unrelated sporadic cases of the same disease
Rule out cases of similar but unrelated diseases (e.g. Yellow Fever and Hep A in Uganda in 2010)
Understand seasonal variability of diseases
Population changes are important –> need population denominators to calculate incidence. an INCREASE in the number of cases accompanying population movements may or may not represent increasing incidence

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From the 10 steps of an outbreak investigations:

Step 3: Verify the diagnosis

How do you do this?

Enture proper diagnosis
- obtein medical and lab reports
- discuss with health personnel
- talk to the people who have been affected

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From the 10 steps of an outbreak investigations:

Step 4: Define and identify cases

How do you do this?

standardise a set of criteria based on:

Clinical Infomation (Signs, symps, lab info_
Place (location of suspected exposure)
Timing (based on incubation)
Systematically find cases and record information –> demograohic info, clinical info, risk factor info
Data should be collected into a standardise case reporting form

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What is the difference between a confirmed case and a probable case?

CONFIRMED: lab diagnosis confirmation

PROBABLE: typical clinical features without a conclusive lab diagnosis

SUSPECTED: usually fewer clinical features
May become more or less likely as the case definition changes with outbreak evolution

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What is Sensitivity?

% of true positives correctly identified

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What is specificity?

% of true negatives correctly identifies

What are the pros and cons of choosing sensitivity vs specificity in outbreak case definitions

Trade-off between sensitivity & specificity
– Highly sensitive CD will usually not be very specific, and vice versa

– Decisions need to be taken as to what is priority

Implications of false negatives (e.g. Ebola in the community)
Implications of false positives (e.g. non-cases in ETCs)
Priorities may shift over course of outbreak (narrow down when clinical spectrum becomes more clear)
This uncertainty leads to confirmed, probable and suspected CDs

From the 10 steps of an outbreak investigations:

Step 5: perform descriptive epidemiology

How do you do this?

Use your data to characterise an outbreak by time, place and person
- describe timing, geography and people affected (as per your definition!)

Compare the outbreak to the usual trends of the disease
- usual source, mode of transmission, risk factor

How do you collate the data from epidemiological information you have gathered?

Analyse cases based on TIME (Epi-Curve) creating an Epidemic curve
Analyse cases based on PLACE by creating a Spot Map
Analyse cases based on PERSON (by creating a population chart or graph

What is an Epi-Cruve

– Graph of number of new cases per unit time
(usually by onset, occasionally presentation)
– Visual display of magnitude & time trend of
outbreak
* Correlated events can be added to the graph
– Helps establish where we are in course of
outbreak and project future course
* Is incidence increasing, decreasing or stable? –> helps you to project further cases

Why can it be helpful to create an ‘Epi Curve’

Suggest type of exposure (shape of epi curve)
Suggest probable period of exposure
– If agent known
Suggest possible agents
– If period of exposure known
– Compare with list of known incubation periods to help identify agent

What is the Point Source?

Same source, exposure period is brief
All cases occur within one incubation period

What is a continuous point source?

Exposure occurs over multiple incubation periods

What is an intermittent point source?

* Exposure to same harmful influence (e.g. infectious agent or toxin) from same source (e.g. contaminated water) * Does not spread

What is a propagated source?

Transmission occurs from person to person rather than a common source

What is a Spot Map?

The most basic form of mapping an outbreak, centre on likely places of exposure ** Does not take into account underlying population distributions, so maps showing incidence RATES are preferable to showing individual cases

From the 10 steps of an outbreak investigations: Step 6: Develop a hyopthesis How do you do this?

Intelligent guesses before you have all of your data. You can determine it with or without all of the following information: – Causative agent – Mode(s) of transmission – Exposure(s) causing the disease – Outlier cases can sometimes provide important clues

From the 10 steps of an outbreak investigations: Step 7: Evaluate and refine your hypothesis How do you do this?

Combine your Epi, lab and environmental data and put this through your hypothesis testing Analyse the data - Retrospective cohort studies

From the 10 steps of an outbreak investigations: Step 7: Evaluate and refine your hypothesis How do you do this?

Combine your Epi, lab and environmental data and put this through your hypothesis testing Analyse the data - Retrospective cohort studies - Case control studies Generate a new hypothesis by looking at your data

When is a retrospective cohort useful?

- Small, well definited populations - Useful to compare attack rates (AR) for the exposed and unexposed - Helps to identify sources - Data expressed as RISK NOTE: Risk Ratio around 1 = likely something isn't a risk Risk Ratio >1 = something likely is a significant risk

When might you use a Case-Control Study?

Useful when the population is NOT well defined Compare exposures between case-patients and controls (same population but with disease vs no disease) You cannot calculated attack rates beucase the totals of exposed and unexposed are unknown (different compared to retrospective) Data expressed as an ODDS RATIO

How do you calculate an Odds Ratio?

* Odds of eating at restaurant among case patients = a/c = 30/10 = 3 * Odds of eating at restaurant among controls = b/d = 36/70 = 0.51 * Odds ratio = 3/0.51 = 5.8

From the 10 steps of an outbreak investigations: Step 8: implement control and prevention measures. How do you do this?

Use results to help guide your Rx and Prevention measures - allows you to provide evidence based interventions - implement this as soon as possible e.g. Measles outbreak in the Ddaab refugee camp in 2012 with an unusual age distribution (loads of adults!) --> meant you had to target vax campaigns and nutrition against adults too

From the 10 steps of an outbreak investigations: Step 9: Initiate/strengthen surveillance How do you do this?

Determine appropriate duration of surveillance based on the incubation period of the disease e.g. Declare a place as ebola-free after DOUBLE the maximum incubation period (eg. incubation is 21 days so surveil for 42 days)

From the 10 steps of an outbreak investigations: Step 10: Communicate your findings How do you do this?

Feedback to the MoH Communitcate health messages to the population

In what situations do humanitarians work?

- Rapid onsetting disasters (e.g earthquakes) - Slow onsetting disaster (e.g. drought and famine) - Conflict and post-conflict - Pandemics and epidemics - Migration

What are the core humanitarian principles

1. Neutrality - must not take sides; not promoting a political idea etc 2. Impartiality - giving action based on priority and nothing else 3. Independence - autonomous from the political objectives of any actors in the area 4. Humanity / humanitarian imperative

What kind of relief to Humanitarian Aids provide?

Water, Sanitation and Hygiene Shelter Protection Nutrition Logistics Health Food and Security Emergency telecommunications Educations Early Recovery Camp Co-ordination and camp management

What are potential ‘Project Dynamic Problems” in a humanitarian project?

- HR —> e.g. staff are employed by MoH but paid by NGO - Hospital vs external activities - NGO vs MoH agenda —> they must depend on each other to work well - Acceptance and security —> safety, conflicts with community/staff - Security influenced by three things: Acceptance from the local area that the NGO is beneficial, and therefore are not attacked, PROTECTION as a passive approach to reducing risk, DETERRENCE as active methods to prevent danger

In regards to a humanitarian project, what is a Mission Creep?

- Adaptations and changes which occur on a mission if there is no clear end or exit - e.g. Expansion of capacity (patients come from afar if they know the healthcare will be good) - e.g. expansion of services - E.g. expansion of activities —> burden in hospital increases, so you start to offer community health