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Information for action: Principles of surveillance

This course provides preliminary questions, a session outline, and definitions of epidemiology and surveillance to enhance the understanding and use of surveillance information for public health decision-making.

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Information for action: Principles of surveillance

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  1. Information for action:Principles of surveillance Integrated Disease Surveillance Programme (IDSP) district surveillance officers (DSO) course

  2. 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? 2

  3. Outline of the session • Surveillance definition • Data collection • Data analysis • Use of surveillance information for action 3

  4. 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) 4 Surveillance

  5. 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? 5 Surveillance

  6. 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? 6 Surveillance

  7. A common vision of surveillance Ministry of Health State Is this surveillance? or “case reporting”? Could we work any other way? District 7 Surveillance

  8. Collect and transmit data Make decisions Analyzedata Feedbackinformation A dynamic vision of surveillance All levels use information to make decisions The private sector can treat patients butonly the public sector can coordinate surveillance 8 Surveillance

  9. 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 9 Surveillance

  10. 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 10 Surveillance

  11. 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 11 Surveillance

  12. 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 Critical stage:This is where the numbers start to make sense 12 Surveillance

  13. What is contained in the definition of public health surveillance? • Systematic • Data collection • Transmission • Analysis • Feedback • Contains structured information • Stimulates reporting • Decision making 13 Surveillance

  14. 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 data 14 Surveillance

  15. 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 Data collection 15

  16. 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 Being clear about what a case definition is and is not Data collection 16

  17. 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 CDC for TLP 17

  18. TIME analysis = Epidemic curve Cases of diarrhea by date of onset, Garulia, West Bengal, 2006 (n=298) Attack rate: 4 per 1000; No deaths 4 5 4 0 3 5 r e p a i r o f C h l o r i n a t i o n o f p i p e l i n e 3 0 o v e r h e a d - t a n k l e a k a g e s 2 5 No. of cases 2 0 1 5 1 0 5 0 18 4 6 8 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 10 A p r i l D a t e o f O n s e t M a y

  19. PLACE analysis= Map Distribution of diarrhea cases by households, Garulia, West Bengal, India, 2006 Index case Household with 1 case Household with 2-3 cases Household with 4-5 cases Household with 6+ cases Water pipeline Road Overhead tank Leakage point CDC for TLP 19

  20. PERSON analysis = Table Attack rate of diarrhea by age and sex, Garulia, West Bengal, India, 2006 CDC for TLP 20

  21. 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 21

  22. Usefulness of surveillance data • 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) Use 22

  23. 45 40 35 30 25 20 15 10 5 0 May July July July July July May May May May April April April April April June June June June June February March March March March March August August August August August January October January October January October January October January October February February February February November December November December November December November December November December September September September September September Assess trends Malaria in Kurseong block, Darjeeling District, West Bengal, India, 2000-2004 Incidence of malaria Incidence of Pf malaria Incidence of malaria per 10,000 2000 2001 2002 2003 2004 Months Decision: Investigate recent increase of incidence Use 23

  24. Detect outbreaks Incidence of diarrhea in Parbatia and the rest of its Primary health Centre (PHC), Orissa, India, November 2001-3 5 4 PHC Village 3 Incidence (%) 2 1 0 2001 Nov 2002 Nov 2003 Nov Months Decision: Investigate the outbreak Use 24

  25. 7 5 3 6 4 2 1 Identify risk factors Diphtheria incidence in Hyderabad, Andhra Pradesh, 2003-6 Attack rates per 100,000 <5 10-14 15-19 20-25 89% of cases are from circles 1-4 with high proportion of Muslim community Decision: Assess coverage among Muslims Use 25

  26. Popu l atio n Cases Incid e nce p er 1 , 0 0 0 (Mil l ions) A g e g rou p 0 - 1 0.06 107 1.8 1 - 4 0.26 1,5 6 9 6.0 5 - 14 0.65 3,5 8 5 5.5 15+ 1.53 5,2 3 7 3.4 Se x Male 1.3 5,9 1 5 4.6 Fe m ale 1.2 4,5 8 3 3.8 T otal 2.5 10, 4 98 4.2 Estimate burden Incidence of malaria by age and sex, Purulia, West Bengal, India, 2004 Decision: Large burden: Evaluate the programme Use 26

  27. Attack rate per 10,000 500+ 200-499 20-199 0-19 Pond Forest Old well River Raise hypotheses during outbreaks Malaria rates in Sukna, Darjeeling, West Bengal, India, 2005 Use Decision: Investigate and cover the wells 27

  28. Evaluate the impact of programmes Reported Yaws cases, India, 1996-2007 (June) 4000 3500 3000 2500 Number of cases 2000 1500 1000 500 0 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 June '07 Year Decision: Engage certification Use 28

  29. 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 29

  30. 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 30

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