Transcript Getting to the essential

Information for action:
Principles of surveillance
Integrated Disease Surveillance Programme (IDSP)
district surveillance officers (DSO) course
Preliminary questions to the group
• Were you already involved in surveillance?
• If yes, what difficulties did you face?
• What would you like to learn about
surveillance?
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Outline of the session
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Surveillance definition
Data collection
Data analysis
Use of surveillance information for action
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Definition of epidemiology
Epidemiology is the study of the distribution
and determinants of health-related events or
states in population groups and the application
of this study to the control of health problems
(Last JM ed. Dictionary of Epidemiology, Oxford University Press, 1995)
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Surveillance
Surveillance:
A role of the public health system
The systematic process of collection,
transmission, analysis and feedback of public
health data for decision making
Could you drive
without looking at the traffic?
Can you make public health
decisions in the absence of data?
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Surveillance
Information collected by the surveillance
system
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Who get the disease?
How many get them?
Where they get them?
When they get them?
Why they get them?
What needs to be done as response?
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Surveillance
A common vision of surveillance
Ministry of Health
Is this surveillance?
or “case reporting”?
State
Could we work any other way?
District
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Surveillance
A dynamic vision of surveillance
Collect and
transmit
Make
decisions
data
All levels use
information
to make
decisions
Analyze
data
Feedback
information
The private sector can treat patients but
only the public sector can coordinate surveillance
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Surveillance
What is contained in the definition of
public health surveillance?
• Systematic
 Ongoing, routine process
 Consistent, generates a baseline
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Data collection
Transmission
Analysis
Feedback
Decision making
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Surveillance
What is contained in the definition of
public health surveillance?
• Systematic
• Data collection
 Cases defined precisely and counted consistently
 Not ALL cases, just the SAME types of cases every
day
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Transmission
Analysis
Feedback
Decision making
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Surveillance
What is contained in the definition of
public health surveillance?
• Systematic
• Data collection
• Transmission
 Regular data transmission
 Ongoing communication methods
 Data are looked at before they are passed on
• Analysis
• Feedback
• Decision making
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Surveillance
What is contained in the definition of
public health surveillance?
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Systematic
Data collection
Transmission
Analysis
Critical stage:
This is where the numbers
start to make sense
 Raw data converted into information
 Case counts become rates
• Feedback
• Decision making
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Surveillance
What is contained in the definition of
public health surveillance?
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Systematic
Data collection
Transmission
Analysis
Feedback
 Contains structured information
 Stimulates reporting
• Decision making
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Surveillance
What is contained in the definition of
public health surveillance?
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Systematic
Data collection
Transmission
Analysis
Feedback
Decision making
 Decision making justifies the investment
 Use of information improves the data
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Surveillance
Case definition:
The keystone of surveillance
• Can you count if you do not know what you are
supposed to count?
• Can you report if you don’t know what you are
supposed to report?
• Different persons may define a disease differently:
 Malaria = Fever (Health worker)
 Malaria = Fever and splenomegaly (Doctor)
 Malaria = Fever with positive slide (Laboratory)
• Harmonization of these different criteria is needed
 The system does not need to be exact, true or perfect
 The system just needs to be consistent every day
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Data collection
Being clear about what
a case definition is and is not
 YES
• A case is an event
• An event is something
that happens to:
 NO
• A case is not a person
• Events cannot be
considered if you lack:
 A person,
 In a given place,
 At a given time
 Person characteristics
 Location
 Onset date
• A case definition is a
set of criteria that
triggers reporting
• A case definition is not
a diagnosis that decides
the treatment
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Data collection
Analysis of surveillance data
• Count, Divide and Compare (CDC)
 Count
• Define cases to know what you count
 Divide
• Divide cases by the population denominator
(The denominator must match the numerator)
 Compare
• Compare rates across groups
• Time, place and person analysis
See cholera outbreak example of time,
place and person analysis in the following slides
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CDC for TLP
TIME analysis = Epidemic curve
Cases of diarrhea by date of onset,
Garulia, West Bengal, 2006 (n=298)
Attack rate: 4 per 1000; No deaths
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40
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repair of
Chlorination of pipeline
overhead-tank leakages
No. of cases
30
25
20
15
10
5
0
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April
Date of Onset
May
PLACE analysis= Map
Distribution of diarrhea cases by households,
Garulia, West Bengal, India, 2006
Index case
Household with
Household with
Household with
Household with
1 case
2-3 cases
4-5 cases
6+ cases
Water pipeline
Road
Overhead tank
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Leakage
point
CDC for TLP
PERSON analysis = Table
Attack rate of diarrhea by age and sex,
Garulia, West Bengal, India, 2006
Characteristics
Age
Gender
Number of
cases
Population,
2006
Attack rate
per 1,000
0-4
51
8,030
6.4
5 -14
68
20,066
3.4
15 - 24
39
15,493
2.5
25 - 34
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14,107
3.0
35 - 44
42
11,191
3.8
45 +
56
15,637
3.6
Male
158
43,716
3.6
Female
140
40,809
3.4
Total
298
84,525
3.5
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CDC for TLP
Conclusions of the analysis of
surveillance data in this example
• There is an outbreak of diarrhoea
 Rectal swabs confirmed the diagnosis cholera
• It affects a specific area supplied by a
pipeline that leaked
• Age distribution is compatible with cholera
Decision: Investigate the source, examine the pipeline
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CDC for TLP
Usefulness of surveillance data
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Describe trends
Detect outbreaks
Identify risk factors
Estimate burden
Generate hypotheses during outbreaks
Evaluate programmes
See examples for each of these uses in the following slides
(Note the action point for each piece of information)
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Use
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0
2000
2001
2002
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2003
May
June
July
August
September
October
November
December
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February
March
April
May
June
July
August
September
October
November
December
January
February
March
April
May
June
July
August
September
October
November
December
January
February
March
April
January
February
March
April
May
June
July
August
September
October
November
December
January
February
March
April
May
June
July
August
September
October
November
December
January
Incidence of malaria per 10,000
Assess trends
Malaria in Kurseong block, Darjeeling
District, West Bengal, India, 2000-2004
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Incidence of malaria
Incidence of Pf malaria
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20
15
10
5
2004
Months
Decision: Investigate recent increase of incidence
Use
Detect outbreaks
Incidence of diarrhea in Parbatia and the
rest of its Primary health Centre (PHC),
Orissa, India, November 2001-3
Incidence (%)
5
4
PHC
Village
3
2
1
0
2001 Nov
2002 Nov
2003 Nov
Months
Decision: Investigate the outbreak
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Use
Identify risk factors
Diphtheria incidence in Hyderabad,
Andhra Pradesh, 2003-6
Attack rates per 100,000
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5
10-14
3
6
4
<5
15-19
20-25
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1
Decision: Assess coverage among Muslims
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89% of cases are from
circles 1-4 with high
proportion of Muslim
community
Use
Estimate burden
Incidence of malaria by age and sex,
Purulia, West Bengal, India, 2004
Population
Cases
Incidence per 1,000
(Millions)
Age group
Sex
0-1
0.06
107
1.8
1-4
0.26
1,569
6.0
5-14
0.65
3,585
5.5
15+
1.53
5,237
3.4
Male
1.3
5,915
4.6
Female
1.2
4,583
3.8
2.5
10,498
4.2
Total
Decision: Large burden: Evaluate the programme
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Use
Raise hypotheses during outbreaks
Malaria rates in Sukna, Darjeeling,
West Bengal, India, 2005
Attack rate
per 10,000
500+
200-499
20-199
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Pond
Forest
Old well
River
Decision: Investigate and cover the wells
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Use
Evaluate the impact of programmes
Reported Yaws cases, India, 1996-2007 (June)
4000
3500
Number
of cases
3000
2500
2000
1500
1000
500
0
Year
Decision: Engage certification
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Use
Take home messages
• Surveillance is a lively line of communication
that works both way
 From bottom to top and from top to bottom
• A surveillance system counts the same
events, consistently, every day
• Count, divide and compare to generate
information on time, place and person
 CDC for TPP
• Surveillance guides decisions
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Practical organization of this course
• Didactic sessions
 Lectures
 Case study
• Field exercise
 Surveillance data analysis
• Field assignment
 As you will go back to your district, we ask you to
analyze surveillance data and send a short report
to the institution
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