Outbreak Investigations Flashcards
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
Which diseases are considered an ‘outbreak’ with just one case?
Polio
Ebola
What would the R number be in endemic areas of disease transmission?
R = 1 (roughly)
Epidemics occur in ENDEMIC areas when R >1
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
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
What is the definition of Pandemic?
An epidemic that has a global reach, crossing international boundaries & affecting large numbers
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
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
What is PHEIC?
Public Health Emergency of International Concern
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
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
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
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
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
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
What is Sensitivity?
% of true positives correctly identified
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
- Neutrality - must not take sides; not promoting a political idea etc
- Impartiality - giving action based on priority and nothing else
- Independence - autonomous from the political objectives of any actors in the area
- 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
