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E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Computerized EWAR systems
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Surveillance system
EWAR
Event based Case based
Report
signal
Report
signal
Outbreak investigationEvaluation
Introduction to surveillance
Role of IHR
EWAR •Structure,•Prioritization of diseases,•Case definitions
Signal generation
and verification
GIS
System evaluation
Outbreak investigation
Alert
Routineweekly, monthly and quarterly reporting
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Objectives of this lecture
• To describe the structure of EWAR systems applied to computer applications,
• To define the meaning of alert signals and give an overview of the methods used to calculate thresholds
• To present examples of existing EWAR systems in national and international context.
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Function of a surveillance system
aiming to detect any abnormal
phenomenon that will trigger prompt
public health interventions
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
Early Warning
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Early warning and response
Report Data
Public health alert
CaptureFilterVerify
CollectAnalyseInterpret
Assess
Surveillance:
Response
Event-based surveillance Case-based surveillance
Post-outbreak strengthening Evaluate
InvestigateControl
Signal
Strengthen
Report Data
Public health alert
CaptureFilterVerify
CollectAnalyseInterpret
Assess
Surveillance:
Response
Event-based surveillance Case-based surveillance
Post-outbreak strengthening Evaluate
InvestigateControl
Signal
Strengthen
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
The components of a computerized EWARN System
• Data collection– Data entry– Data import from an existing system
• Data analysis• Generation of signals• Presentation of results• Generation of reports
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Computerized EWAR systems
Standardization of:
– Data collection
– Data flow
– Data exchange
Better data quality
Faster data availability
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
• Automated report generation with updated data
• Customized reports
– Optimized presentation
• Interactive browsing/exploration of data
• Information on demand
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
Computerized EWAR systems
Easier, faster feedback
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
• Improved and faster analysis,
• Larger datasets can be analysed,
• Use of different algorithms ,
• Automated signal generation, and
flagging of situation for immediate
attention.
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
Computerized EWAR systems
Rapid response
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Signals
A signal is something that could
indicate the impending occurrence
of an event.
(WHO SEARO Early Warning and Response to Outbreaks and other Public Health Events: A Guide)
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Nature of the health event– Massive and sudden
• Common point source (Salmonellosis…)
– Diffuse and progressive
• Person to person (Shigellosis, Hepatitis…)
– Sporadic and widespread
• Persistent common source (salmonella,
listeria in food chain, legionella…)
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
EWARN – Thresholds
Local epidemiology of the disease
• Endemic/hyper-endemic/epidemic
• Seasonal/non seasonal
• Rare/common
• Outbreak distribution type (eg. point
source rather than persistent or
propagated source)
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Thresholds can be based on
• Absolute numbers
• Rates
• Relative changes over time
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Methods based on the number of cases of disease
(predefined thresholds)• Number of cases
– One case of measles
(Refugee Camp)
• Number of cases / population / time
– Epidemic threshold: 10 Cases of meningitis /
100000 /week
(Meningitis belt)
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Predefined Thresholds
+ -Easy to interpret and to
communicate
How to deal with seasonal patterns and
trends
No historical data needed
Increase from 2 to 4 the same like 2000 to
4000?
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Methods based on changes over time
• Increase of cases
– Cases in week 24 1.5 x higher than mean for last 4
weeks
• Doubling of cases over a given time period
– Doubling of cases over 3 weeks period
(Meningitis belt – small districts)
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Crude data
0
1
2
3
4
5
6
7
8
1 51 101 151 201 251Time
Cas
es
Presentation of surveillance EWAR data
crude data
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
0
20
40
60
80
100
Signal
0
25
50
Secular trend
0
25
50
-25
Seasonal factor
50
0
25
Residual signal
Presentation of surveillance EWAR data
time series
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Moving average, 15 weeks
0
1
2
3
4
5
6
7
8
1 51 101 151 201 251Time
Ca
se
s
For weekly data:a smoothing average of 5 to 15 weeks highlights the seasonality
Presentation of surveillance EWAR data
seasonal pattern
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Moving average, 52 weeks
0
1
2
3
4
5
6
7
8
1 51 101 151 201 251
Time
Cas
es
For weekly data: smoothing average of 52 weeks highlights the trend
Presentation of surveillance EWAR data
long term pattern
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Examples of early warning systems
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Meningitis in
sub-saharan Africa
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Objectives of the meningitis surveillance system
• Timely detection of outbreaks
• Immediate confirmation of the outbreak
• Identification of pathogen and serogroup
• Rapid response
– Vaccination
– Proper case management
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Meningitis surveillance system
• Meningitis one out of 10 diseases
• Integrated Disease Surveillance
• Weekly notifications aggregated data to district level
– Suspected cases
– Deaths
– District National Level Region (Burkina
Faso)
• Immediate reporting when district crossed threshold
• Zero reporting
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Thresholds for meningitis in the meningitis belt
Districts > 30 000 population
Incidence (weekly)
Districts < 30 000 population
Cases (per week)
Doubling of cases
Alert >= 5/ 100 000Epidemic >=10/ 100 000
Alert >= 2Epidemic >= 5
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Thresholds for meningitis in the meningitis belt
Alert / Epidemic → Epidemic /Epidemic
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Crossing thresholds actions to be taken
Alert threshold vs
Epidemic threshold
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Objectives of the EWAR and Reporting System for
Meningitis
1. Combine timely information from the
whole region.
2. Share information across the region,
3. Flag districts in alert or epidemics,
4. Give an estimate of persons at risk, and
5. Give an overview of circulating sero-
groups.
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Country Indicator Districts in Completness Pathogens
Cases DeathsCFR
%Alert Epid Weeks Districts
Weeks %
Nm.AW13
5
Other
Nm
Pneum
Hib
Benin 294 72 24.5 4 0 01-37 77/77 99.9 23 6 1 47 1
Burkina Faso 5586 980 17.5 13 5 01-37 55/55 100.0 128 66 0 177 44
Côte d’Ivoire 373 66 17.7 0 1 01-37 44/65 82.2 11 0 0 0 0
Ethiopie 2768 146 5.3 4 5 01-20 ND 52.5 48 0 2 1 0
Ghana 949 143 15.0 4 1 01-37 56/110 37.3 49 2 0 0 0
Mali 1080 50 4.6 0 1 01-32 58/58 87.5 12 4 0 30 16
Niger 3899 309 7.9 7 3 01-37 42/42 99.9 361 33 20 118 34
Tchad 863 143 16.5 2 1 01-26 51/108 56.0 3 0 0 16 8
Togo 281 41 14.6 0 0 01-37 35/35 96.9 19 1 0 18 2
Total 28461 3608 12.7 53 24 656 112 23 409 107
WHOWorld Health Organization
MDSCMulti Disease Surveillance
Center
CommentsLaboratory data for Niger updated for week 37.No relevant change of the situation compared to last week.
I. Synthesis of the epidemiologic situation up (week 01-2004 to 37-2004)
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Example of map showing districts in alert and epidemic in the meningitis belt
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Summary of alerts and epidemics by country
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Districts of one country currently affected
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Detailed Information for one country - I
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Detailed Information for one country - II
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Olympic Games Athens 2004
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Enhanced Surveillance
• Mandatory System
• Syndromic Systems
• Sentinel System
• Laboratory System
• Hospitals, Physicians, Olympic sites
• Different regions/districts
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
Daily reporting including zero reporting
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Computer ApplicationEWARN and reporting
• Automated output generation
– Daily report
– Detailed internal report
– Signal lists (Alerts)
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
Embedded in an interactive HTML system
–Signal tracking
–Alert tracking
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Global and disease specific outputs - Athens
Information on selected diseases / syndromes
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Signals
• Two statistical methods for threshold calculation
were applied:
– Poisson test
– Binominal test
• Colour coding
– yellow p-value<= 0.05, red p-value<=0.01
• For syndromic surveillance system Olympic
hospitals only
– Additional tests applied
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
Disease specific outputs - Athens
Graphs
Tables
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
• Signal lists of all diseases / syndromes withstatistical tests result (p-value) below the predefined thresholds
Signals Olympic Game Hospitals
Signals laboratory system
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
Disease specific outputs - Athens
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Signal tracking system
• Generation of printable lists for the daily meeting
• Self updating Excel Database for signal tracking
Definition
Structure
Computerbased EWAR
systems
Signals
Thresholdcalculationoverview
EWARexamples
E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module
Question Time
1. Why would you need to define thresholds for
your diseases under EWAR surveillance?
2. What is the limit of predefined thresholds?
3. Based on your current knowledge what would
you say the strengths/weaknesses of the
EWAR systems implemented in Africa and
Athens?
