SEARO –CSR Early Warning and Surveillance System Module Case Definitions.

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EP ID E M IC A LE R T A N D RESPO NSE SEARO –CSR Early Warning and Surveillance System Module Case Definitions

Transcript of SEARO –CSR Early Warning and Surveillance System Module Case Definitions.

Page 1: SEARO –CSR Early Warning and Surveillance System Module Case Definitions.

E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module

Case Definitions

Page 2: SEARO –CSR Early Warning and Surveillance System Module Case Definitions.

E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module

Objectives of this lecture

To identify: • The elements that should be included in a case

definition, • The type of case definitions, and • The balance between sensitive and specific

case definitions.

Page 3: SEARO –CSR Early Warning and Surveillance System Module Case Definitions.

E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module

Case Definition

• Essential tool in a surveillance system

• A case definition for each health event

• Different health events

– Mutually exclusive case definitions

• Consistency in reporting

• Surveillance ≠ patient management

Definition

Elements

Characteristics

SE vs SP

PPV

Post outbreakSARS

WHO standards

Page 4: SEARO –CSR Early Warning and Surveillance System Module Case Definitions.

E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module

Elements of a case definition

• Clinical

• Laboratory diagnosis (if relevant)

• Criteria for place

• Criteria for person

• Epidemiological link (if relevant)

Definition

Elements

Characteristics

SE vs SP

PPV

Post outbreakSARS

WHO standards

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E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module

Types of case definitions

Health events:– disease (rabies)

– syndrome (AFP)

– public health issue (AMR)

– environment (animal vector)

Clinical / Laboratory

Multilevels– Suspected

– Probable

– Confirmed

Specific / Sensitive

Definition

Elements

Characteristics

SE vs SP

PPV

Post outbreakSARS

WHO standards

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E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module

Case definitions should be• Simple / Clear

• Adapted to – Staff qualification– Available diagnostic

• Stable

• Standardized

• Available at all reporting levels– Health posts / health centres– Hospitals– Laboratories

Definition

Elements

Characteristics

SE vs SP

PPV

Post outbreakSARS

WHO standards

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E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module

Levels• Suspected case

– Clinical signs and symptoms

– No laboratory evidence 

• Probable case– Suspect case + supportive lab (eg: single high titre)

– Suspect case + epi link (eg: contact with confirmed case)

• Confirmed case– Laboratory evidence

Cholera

Suspected: Acute watery diarrhoea

Confirmed: Isolation of Vibrio cholerae

Cholera

Suspected: Acute watery diarrhoea

Confirmed: Isolation of Vibrio cholerae

Definition

Elements

Characteristics

SE vs SP

PPV

Post outbreakSARS

WHO standards

Page 8: SEARO –CSR Early Warning and Surveillance System Module Case Definitions.

E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module

Ministryof Health

WHO

Peripheral level

Intermediate level

Central level

Regional/International level

Clinical

(suspected)

+ Supportive laboratory data + epi

link (probable)

Diagnostic Laboratory (confirmed)

Regional reference laboratory

Definition

Elements

Characteristics

SE vs SP

PPV

Post outbreakSARS

WHO standards

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E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module

Exposed

Clinical specimen

Symptoms

Pos. specimen

Infected

Seek medical attention

Report

Sensitivity

Proportion of true cases detected

=

reported true cases

total true cases

Definition

Elements

Characteristics

SE vs SP

PPV

Post outbreakSARS

WHO standards

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E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module

Sensitivity (SE) vs Specificity (SP)

Higher sensitivity vs lower sensitivity depends on the objective

SE

SP

Definition

Elements

Characteristics

SE vs SP

PPV

Post outbreakSARS

WHO standards

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E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module

Positive predictive value

Sick

No

tifi

edYes

Yes No

Total not notified

True -

False +

False -

True + Total notified

No

PPV = True+ / Total notified

Total sick Total not sick

Proportion of reported cases that have the health event under

surveillance

Definition

Elements

Characteristics

SE vs SP

PPV

Post outbreakSARS

WHO standards

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E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module

• PPV depends on

- sensitivity

- specificity

- prevalence of the condition in the population

• Consequence of a low PPV– frequent "false-positive" report

- inappropriate follow-up of non-cases

- incorrect identification of epidemics (artifacts)

- wastage of resources

- inappropriate public concern (credibility)

Definition

Elements

Characteristics

SE vs SP

PPV

Post outbreakSARS

WHO standards

Positive predictive value

Page 13: SEARO –CSR Early Warning and Surveillance System Module Case Definitions.

E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module

Definition

Elements

Characteristics

SE vs SP

PPV

Post outbreakSARS

WHO standards

SARS Re-emergenceRisk assessment

Potential zone of re-

emergence of SARS-CoV

Nodal areas

Low risk areas

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E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module

SARS Syndromic Surveillance, 2003

Underlying assumptions

Definition

Elements

Characteristics

SE vs SP

PPV

Post outbreakSARS

WHO standards

The first cases or clusters of SARS may be missed

Diffuse-progressive nature of the health event.

SARS has aspecific clinical features and no rapid diagnostic test is available

–Clinical features of the disease

–Diagnostic capacity

Seasonal occurrence of other respiratory diseases (influenza, other CoV)

Epidemiological pattern of diseases with similar clinical characteristics in the region.

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E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module

Definition of a SARS “Alert” for EWAR

• 2 or > Health Care Workers

– in same Health care unit (HCU)

– fulfilling clinical case definition of SARS

– with onset of illness in the same 10-day

period

OR

• Hospital acquired illness in 3 or >

persons

– in same HCU

– fulfilling clinical case definition of SARS

– with onset of illness in the same 10-day

period

• 2 or > Health Care Workers

– in same Health care unit (HCU)

– fulfilling clinical case definition of SARS

– with onset of illness in the same 10-day

period

OR

• Hospital acquired illness in 3 or >

persons

– in same HCU

– fulfilling clinical case definition of SARS

– with onset of illness in the same 10-day

period

Definition

Elements

Characteristics

SE vs SP

PPV

Post outbreakSARS

WHO standards

  A person presenting after 1 November 2002 with history of: -  high fever (>38 °C) AND -   One or more symptoms of lower respiratory tract illness AND Radiographic or autoptic evidence consistent with pneumonia or RDS ANDNo alternative diagnosis can fully explain the illness

  A person presenting after 1 November 2002 with history of: -  high fever (>38 °C) AND -   One or more symptoms of lower respiratory tract illness AND Radiographic or autoptic evidence consistent with pneumonia or RDS ANDNo alternative diagnosis can fully explain the illness

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E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module

SARS Clinical case definitionFever (38°C) AND

– One or more symptoms of lower respiratory tract illness (cough, difficulty of breathing, shortness of breath)

AND– Radiographic evidence of

lung infiltrates consistent with pneumonia or RDS

– OR autopsy findings consistent with the pathology of pneumonia or RDS without an identifiable cause

AND– No alternative diagnosis can

fully explain the illness

Definition

Elements

Characteristics

SE vs SP

PPV

Post outbreakSARS

WHO standards

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E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module

Post-outbreakCase definition

Post-Outbreak Case-Definitions

Outbreak case definition

Definition

Elements

Characteristics

SE vs SP

PPV

Post outbreakSARS

WHO standards

Clinical SARSAtypical pneumonia

Suspect

Probable

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E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module

SARS Laboratory case definition

• PCR positive for SARS-CoV ( 2 different clinical specimens OR sequential sampling from the same site OR 2 assays or repeat PCR using a new RNA extract from the original clinical sample on each occasion of testing)

OR

• Seroconversion or 4-fold or greater rise in titre between acute and convalescent phase sera by ELISA or IFA

OR

• Virus isolation with PCR validation

Definition

Elements

Characteristics

SE vs SP

PPV

Post outbreakSARS

WHO standards

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E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module

Aggregatednotification

Syndromic SurveillanceLink with SARS Surveillance

CRF notification

Definition

Elements

Characteristics

SE vs SP

PPV

Post outbreakSARS

WHO standards

Fever + Respiratory

Fever + Respiratory+ chest X-ray

Clinical SARSAtypical pneumonia

Suspect

Probable

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E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module

WHO standards• 48 CD syndromes,

conditions

– same format • Available

english, french, spanish and arabic

• To be adapted to country needs

www.who.int/csr/resources/publications/surveillance/WHO_CDS_CSR_ISR_99_2_EN/en/

Definition

Elements

Characteristics

SE vs SP

PPV

Post outbreakSARS

WHO standards

Page 21: SEARO –CSR Early Warning and Surveillance System Module Case Definitions.

E P I D E M I C A L E R T A N D R E S P O N S E SEARO –CSR Early Warning and Surveillance System Module

Question Time

1. What are the objectives of a case definition?2. How would you approach the design a case

definition for typhoid fever?