SEARO –CSR Early Warning and Surveillance System Module Case Definitions

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.

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 outbreak SARS WHO standards

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 outbreak SARS WHO standards

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 outbreak SARS WHO standards

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 outbreak SARS WHO standards

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 outbreak SARS WHO standards

SEARO –CSR Early Warning and Surveillance System Module Ministry of 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 outbreak SARS WHO standards

SEARO –CSR Early Warning and Surveillance System Module Sensitivity Proportion of true cases detected = reported true cases total true cases Definition Elements Characteristics SE vs SP PPV Post outbreak SARS WHO standards

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 outbreak SARS WHO standards

SEARO –CSR Early Warning and Surveillance System Module Positive predictive value Sick Notified Yes No Total not notified True - False + False - True + Total notified No PPV = True+ / Total notified Total sickTotal not sick Proportion of reported cases that have the health event under surveillance Definition Elements Characteristics SE vs SP PPV Post outbreak SARS WHO standards

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 outbreak SARS WHO standards Positive predictive value

SEARO –CSR Early Warning and Surveillance System Module Definition Elements Characteristics SE vs SP PPV Post outbreak SARS WHO standards SARS Re-emergence Risk assessment Potential zone of re- emergence of SARS-CoV Nodal areas Low risk areas

SEARO –CSR Early Warning and Surveillance System Module SARS Syndromic Surveillance, 2003 Underlying assumptions Definition Elements Characteristics SE vs SP PPV Post outbreak SARS 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.

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 outbreak SARS 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 AND No 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 AND No alternative diagnosis can fully explain the illness

SEARO –CSR Early Warning and Surveillance System Module SARS Clinical case definition Fever (  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 outbreak SARS WHO standards

SEARO –CSR Early Warning and Surveillance System Module Post-outbreak Case definition Post-Outbreak Case-Definitions Outbreak case definition Definition Elements Characteristics SE vs SP PPV Post outbreak SARS WHO standards Clinical SARS Atypical pneumonia Suspect Probable

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 outbreak SARS WHO standards

SEARO –CSR Early Warning and Surveillance System Module Aggregated notification Syndromic Surveillance Link with SARS Surveillance CRF notification Definition Elements Characteristics SE vs SP PPV Post outbreak SARS WHO standards Fever + Respiratory + chest X-ray Clinical SARS Atypical pneumonia Suspect Probable

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 R_ISR_99_2_EN/en / Definition Elements Characteristics SE vs SP PPV Post outbreak SARS WHO standards

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?