Information for action:Principles of surveillance

Integrated Disease Surveillance Programme (IDSP) district surveillance

officers (DSO) course

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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

1. Surveillance definition2. Data collection3. Data analysis4. 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)

Surveillance

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Surveillance: A role of the public health

systemThe systematic process of collection, transmission,

analysis and feedback of public health data for decision making

Surveillance

Could you drive without looking at the traffic?

Can you make public health decisions in the absence of data?

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Information collected by the surveillance system

• 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?

Surveillance

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A common vision of surveillance

District

State

Ministry of Health

Is this surveillance? or “case reporting”?

Could we work any other way?

Surveillance

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A dynamic vision of surveillance

Collect and transmit

data

Analyzedata

Feedbackinformati

on

Make decisions

All levels use information to make decisions

Surveillance

The private sector can treat patients butonly the public sector can coordinate surveillance

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What is contained in the definition of public health

surveillance?• Systematic

Ongoing, routine process Consistent, generates a baseline

• Data collection• Transmission• Analysis• Feedback• Decision making

Surveillance

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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

• Transmission• Analysis• Feedback• Decision making

Surveillance

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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

Surveillance

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What is contained in the definition of public health

surveillance?• Systematic• Data collection• Transmission• Analysis

Raw data converted into information Case counts become rates

• Feedback• Decision making

Surveillance

Critical stage:This is where the numbers

start to make sense

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What is contained in the definition of public health

surveillance?• Systematic• Data collection• Transmission• Analysis• Feedback

Contains structured information Stimulates reporting

• Decision making

Surveillance

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What is contained in the definition of public health

surveillance?• Systematic• Data collection• Transmission• Analysis• Feedback• Decision making

Decision making justifies the investment

Use of information improves the dataSurveillance

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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 dayData collection

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Being clear about what a case definition is and is

not YES

• A case is an event• An event is something that happens to: A person, In a given place, At a given time

• A case definition is a set of criteria that triggers reporting

NO• A case is not a person

• Events cannot be considered if you lack: Person characteristics Location Onset date

• A case definition is not a diagnosis that decides the treatment

Data collection

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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

CDC for TLP

See cholera outbreak example of time, place and person analysis in the following slides

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4 6 8 10 12 14 16 18 20 22 24 26 28 30 2 4 6 8 10April Date of Onset May

No

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case

s

Chlorination of overhead-tank

repair of pipeline leakages

Attack rate: 4 per 1000; No deaths

Cases of diarrhea by date of onset, Garulia, West Bengal,

2006 (n=298)

TIME analysis = Epidemic curve

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Distribution of diarrhea cases by households, Garulia, West Bengal,

India, 2006

Index caseHousehold with 1 caseHousehold with 2-3 cases Household with 4-5 casesHousehold with 6+ cases

Water pipelineRoadOverhead tankLeakage point

PLACE analysis= Map

CDC for TLP

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Attack rate of diarrhea by age and sex, Garulia, West

Bengal, India, 2006Characteristic

sNumber of

casesPopulati

on,2006

Attack rate per 1,000

Age 0 - 4 51 8,030 6.4

5 -14 68 20,066 3.4

15 - 24 39 15,493 2.5

25 - 34 42 14,107 3.0

35 - 44 42 11,191 3.8

45 + 56 15,637 3.6

Gender Male 158 43,716 3.6

Female 140 40,809 3.4

Total 298 84,525 3.5

PERSON analysis = Table

CDC for TLP

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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

CDC for TLP

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Usefulness of surveillance data

• Describe trends• Detect outbreaks• Identify risk factors• Estimate burden• Generate hypotheses during outbreaks

• Evaluate programmes

Use

See examples for each of these uses in the following slides(Note the action point for each piece of information)

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Malaria in Kurseong block, Darjeeling District, West Bengal, India, 2000-2004

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000 Incidence of malaria

Incidence of Pf malaria

Assess trends

Use Decision: Investigate recent increase of incidence

24Decision: Investigate the outbreak

Detect outbreaks

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Incidence of diarrhea in Parbatia and the rest of its Primary health Centre (PHC),

Orissa, India, November 2001-3

Use

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Attack rates per 100,000

89% of cases are from circles 1-4 with high proportion of Muslim

community

<5

10-14

15-19

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Diphtheria incidence in Hyderabad, Andhra Pradesh,

2003-6

Identify risk factors

Use Decision: Assess coverage among Muslims

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Population

(Millions)

Cases Incidence per 1,000

0-1 0.06 107 1.8

1-4 0.26 1,569 6.0

5-14 0.65 3,585 5.5

Age group

15+ 1.53 5,237 3.4

Male 1.3 5,915 4.6 Sex

Female 1.2 4,583 3.8

Total 2.5 10,498 4.2

Incidence of malaria by age and sex, Purulia, West Bengal,

India, 2004

Estimate burden

Use Decision: Large burden: Evaluate the programme

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Attack rate per 10,000

500+

200-499

20-199

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Pond

Old well

Forest

River

Decision: Investigate and cover the wells

Raise hypotheses during outbreaks

Use

Malaria rates in Sukna, Darjeeling,

West Bengal, India, 2005

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Reported Yaws cases, India, 1996-2007 (June)

Decision: Engage certification

Evaluate the impact of programmes

Use

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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