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Detection of unusual events

Detection of unusual events. Integrated Disease Surveillance Programme (IDSP) district surveillance officers (DSO) course. Preliminary questions to the group. Have you ever detected an outbreak? If yes, what difficulties did you face?

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Detection of unusual events

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  1. Detection of unusual events Integrated Disease Surveillance Programme (IDSP) district surveillance officers (DSO) course

  2. Preliminary questions to the group • Have you ever detected an outbreak? • If yes, what difficulties did you face? • What would you like to learn about early outbreak detection? 2

  3. Outline of the session • From denial to vigilance • Early warning signals • Triggers in the Indian Integrated Disease Surveillance Programme (IDSP) 3

  4. Here? Here? Here? Cases of cholera by date of onset, South 24 Parganas, West Bengal, India, May 2006 When to investigate? 30 25 20 Never? Number of cases 15 10 5 0 4 24 25 26 27 28 29 30 1 2 3 4 5 April May

  5. When are outbreaks investigated in your district? • When the first cases occur? • An indication of vigilance • When there is a large cluster? • Shows reactivity • When most cases have occurred? • The team only acts under pressure • Never • Denotes denial Fighting denial 5

  6. Reasons why public health professionals might deny outbreaks • No skills to investigate • Additional work • No intervention to offer • Press pressure • Fears of sanctions Fighting denial 6

  7. Turn challenges into opportunity • Investigation methods can be learned • Investigations become easier with practice • Data guides effective prevention measures • Good investigations impress the press • Leaders appreciate signs that the situation is under control (e.g., ongoing investigation) Fighting denial 7

  8. Improving the outbreak detection situation • The number one obstacle to fight is denial • Once there is a willingness to address outbreaks, technical methods may be used to ensure the earliest possible detection • The system will not go from denial to early detection overnight • But every small progress matters • It is never too late to investigate an outbreak • You will still learn, but it is more difficult Fighting denial 8

  9. Two ways to detect unusual events • Event-based surveillance • Reports of events • Case-based surveillance • Routine surveillance data analysis Early warning 9

  10. Components of early warning surveillance Analyze Filter Signal Signal Validate Verify Surveillance: Case-based surveillance Event-based surveillance Data Reports Alert Response Assess Public health alert InvestigateControl measures Post-outbreak strengthening Evaluate Early warning 10

  11. Two ways to detect unusual events • Event based surveillance • Collect reports • (e.g., toll free line, internet search, press scan) • Filter • Identify signals • Verify • Case base surveillance Early warning 11

  12. Early warning signals for event-based surveillance • Clustering of cases or deaths • Single case of disease of epidemic potential • Acute febrile illness of unknown etiology • Two or more linked cases of meningitis, measles • Unusual isolate • Shifting in age distribution of cases • High vector density • Natural disasters Early warning 12

  13. Sources of information for event-based surveillance • Rumour register in each institution • Standardized format • Investigation for each entry • Tracking system to document follow up • Community informants • Private and public sector • Media • Important source of information, not to neglect • 24 x 7 call centre Early warning 13

  14. Two ways to detect unusual events • Event based surveillance • Case base surveillance • Collect data • Analyze data • Detect signals • Validate signals Early warning 14

  15. Challenges to surveillance data analysis to detect unusual events • Imperfect data • Changes over time • Multiple sources of information • Problem of quality and completeness • Need an in-depth knowledge of the system • Evaluation • To know what is unusual, you need to know what is usual Early warning 15

  16. Sources of false alarm • Changes in the numerator • Increased awareness about a disease • Appointment of a new surveillance person • Acute reporting of old, chronic, cases • Changes in the denominator • Population movements Early warning 16

  17. Triggers in the context of the Indian Integrated Disease Surveillance Programme (IDSP) • Threshold for diseases under surveillance that trigger pre-determined actions at various levels • Based upon the number of cases in weekly report • Trigger levels depend on: • Type of disease • Case fatality (Death / case ratio) • Number of evolving cases • Usual trend in the region Triggers 17

  18. Levels of response to different triggers Triggers 18

  19. Malaria triggers • Trigger 1 • Single case of smear positive in an area where malaria was not present for a minimum of three months • Slide positivity rate doubling over last three months • Single death from clinically /microscopically proven malaria • Single falciparum case of indigenous origin in a free region • Trigger 2: • Two fold rise in malaria in the region over last 3 months • More than five cases of falciparum of indigenous origin Triggers 19 * State may set their own triggers

  20. Cholera triggers • Trigger 1 • A single case of cholera / epidemiologically linked cases of diarrhea • A case of severe dehydration / death due to diarrhea in a patient of >5 years of age • Clustering of cases in a particular village / urban ward where more than 10 houses have at least one case of loose stools irrespective of age per 1000 population • Trigger 2 • More than 20 cases of diarrhea in a village/geographical area of 1000 population Triggers 20

  21. Typhoid fever triggers • Trigger 1 • More than 30 cases in a week from the entire primary health centre area • 5 or more cases per week from one sub-centre of 5,000 population • More than 2 cases from a single village/urban ward/1000 population • Clustering of cases of fever • Trigger 2 • More than 60 cases from a primary health centre or more than 10 cases from a sub-center Triggers 21

  22. Polio trigger • One single case Triggers 22

  23. Plague triggers • Trigger 1 • Rat fall • Trigger 2 • At least 1 probable case of plague in community Triggers 23

  24. Japanese encephalitis triggers • Trigger 1 • Clustering of two or more similar case from a locality in one week • Trigger 2 • More than four cases from a PHC (30,000 population) in one week Triggers 24

  25. Dengue triggers • Trigger 1 • Clustering of two similar case of probable Dengue fever in a village • Single case of Dengue hemorrhagic fever • Trigger 2 • More than four cases of Dengue fever in a village with population of about 1000 Triggers 25

  26. Triggers for syndromic surveillance • Fever • More than 2 similar case in the village (1000 Population) • Diarrhea • See cholera • Acute flaccid paralysis • 1 case • Jaundice • More than two cases of jaundice in different houses irrespective of age in a village or 1000 population Triggers 26

  27. Basic responses to triggers • There are triggers for each condition under surveillance • Various trigger levels may lead to local or broader response • Tables in the operation manual propose standardized actions to take following various triggers • Investigations are needed in addition to standardized actions Triggers 27

  28. Progressive response • Levels of alert are progressively increasing • Unusual signals require filtering / validation • The best chance of detection is to: • Analyze regularly • Be familiar with the time, place and person characteristics of the diseases in your area Triggers 28

  29. Public health events of international concern need to be reported as per new International Health Regulations (IHRs) • Public health events • Sudden serious and unexpected event that require immediate action • Outbreak of epidemic prone diseases • Any other event that may have impact on the health of a community (natural or man-made catastrophes) • International concern • Risk of spread beyond the borders of the affected country (agent/host/environment or capacity to contain the event) Triggers 29

  30. Take home messages • Fight denial by showing what can be usefully done about outbreaks • Investigations • Control measures based on evidence • Consider case-based and event-based surveillance • Recognize triggers and respond to them as per guidelines 30

  31. Additional reading • Section 4 of IDSP operations manual • Module 8 of training manual Triggers 31

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