Presentation is loading. Please wait.

Presentation is loading. Please wait.

Detection of unusual events

Similar presentations

Presentation on theme: "Detection of unusual events"— Presentation transcript:

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? Warm up questions for five minutes. 2

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

4 Cases of cholera by date of onset, South 24 Parganas, West Bengal, India, May 2006
Here? When to investigate? 30 25 20 Here? Number of cases Never? 15 Here? Important slide. This is an outbreak. It could be investigated either at the beginning, when the number of cases is rinsing, at the peak or never. Ideally it should be at the beginning. But in your district, it might be never. So what you want is to progressively improve so that it gets better. But it might not go from no investigations to early investigations overnight. 10 5 24 25 26 4 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 This provides additional explanations on the first slide. The four bullets parallel the four arrows on the graph in the previous slide, providing more detail about what the timing of the investigation wil denote. 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 Often there are many reasons not to investigate. Here are some. Can you think of others? 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) But in fact, each of these “Good reasons not to investigate” can be turned into opportunities. See how each of these bullets on this slide parallel the bullets on the previous slide. 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 More on the same theme: You won’t change the situation overnight. Fighting denial 8

9 Two ways to detect unusual events
Event-based surveillance Reports of events Case-based surveillance Routine surveillance data analysis There are two ways to detect unusual events. Event-based surveillance is about event. It works like the reporter who will capture a story heard. For example: There was an outbreak of gastro-enteritis following a major wedding in a village. Case-based surveillance is about following trends based on regular data analysis to detect unusual rises. For example: There is three times as much measles this month than during the same month last year. Early warning 9

10 Components of early warning surveillance
Case-based surveillance Event-based surveillance Data Reports Analyze Filter Signal Validate Verify Alert Response Assess Whichever system is considered -like on this flowchart- there is a process to transform SIGNALS into ALERTS through either analysis and validation (case based surveillance) or through filtering and verification (event based surveillance). When an alert is given, it leads to response. Public health alert Investigate Control 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 A development of event based surveillance. It works like journalism when a journalist checks a story. 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 These are the kind of events that can be signals to be filtered and verified. 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 To gather events you also need a reporting system. It is as for case surveillance. Early warning 13

14 Two ways to detect unusual events
Event based surveillance Case base surveillance Collect data Analyze data Detect signals Validate signals This is a development of case-based surveillance. 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 It is difficult to do case based surveillance because the system is not perfect. So you must know your system. Like if you know your old car, you will know what is really abnormal among the various noises that it makes. 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 Some causes of false alarm. 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 To make the system easier IDSP has a number of triggers. Triggers 17

18 Levels of response to different triggers
Significance Levels of response 1 Suspected /limited outbreak Local response by health worker and medical officer 2 Outbreak Local and district response by district surveillance officer and rapid response team 3 Confirmed outbreak Local, district and state 4 Wide spread epidemic State level response 5 Disaster response Local, district, state and centre These triggers work by levels that define their significance and anticipate their level of response. Triggers 18

19 Malaria triggers Trigger 1 Trigger 2:
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 for malaria. Triggers 19 * State may set their own triggers

20 Cholera triggers Trigger 1 Trigger 2
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 for cholera. Triggers 20

21 Typhoid fever triggers
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 for typhoid. Triggers 21

22 Polio trigger One single case Triggers for polio. Triggers 22

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

24 Japanese encephalitis triggers
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 for Japanese encephalitis. Triggers 24

25 Dengue triggers Trigger 1 Trigger 2
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 for dengue. 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 for syndromic surveillance. 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 The operation manual defines what to do in view of each trigger. 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 The response may be of increasing magnitude. 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) One specific point is the International Health Regulations. These ask for reporting of public health events of international concern. Those are defined as on this slide. 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 Take home messages. 30

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

Download ppt "Detection of unusual events"

Similar presentations

Ads by Google