Instructions for users This slide presentation provides an overview of the components of a population-based surveillance system for JE. Please use this slide set in conjunction with the WHO- recommended standards for surveillance of selected vaccine-preventable diseases (2003), which was the primary source document for this presentation. Notes below some of the slides explain the information contained in the slide. You should adapt the presentation for your own use. Additional resources are suggested in the notes section below this slide.

Assessing Disease Burden of Japanese Encephalitis: Population-based Surveillance

Learning objectives Participants will: Understand the rationale for and importance of JE surveillance. Become familiar with definitions, methods, and elements of a surveillance system for JE. Understand how to establish and maintain a JE surveillance system.

What is disease surveillance? Disease surveillance is the routine ongoing collection, analysis, and dissemination of health data. An effective surveillance system has the following functions: Detection and notification of health events. Collection and consolidation of pertinent data. Investigation and confirmation (epidemiological, clinical, and/or laboratory) of cases or outbreaks. Routine analysis and creation of reports. Feedback of information to persons providing data. Feed-forward (i.e., the forwarding of data to more central levels).

Why is understanding JE disease burden important? Up to 50,000 cases and 10,000 deaths are reported to WHO each year, mostly among children. However, these figures are known to be grossly under-estimated primarily because of poor diagnostic capability and lack of adequate surveillance systems. The greatest barrier to undertaking JE control is the limited recognition by policy-makers of the public health burden and economic impact of JE disease.

Why is surveillance necessary for JE? (1) In many countries, the epidemiology and public health burden of JE is poorly understood so the main goals of surveillance are to: Describe the epidemiology and burden of JE. Use data to advocate and plan for control of the disease through immunization.

Why is surveillance necessary for JE? (2) In countries with JE immunization programs, the main goals of surveillance are to: Assess the impact of vaccination. Guide where immunization coverage should be improved. Identify new geographical areas or age groups to include in the immunization program. Monitor vaccine efficacy.

Principles in implementation of a surveillance system In implementing a surveillance system, it is important to ensure: The system is streamlined within existing systems. The data collected should be those essential to guide decision-making on public health matters. Only the minimum necessary data should be collected—if data will not be analysed and used, it should not be collected.

Methods of JE surveillance Surveillance for JE normally involves: Syndromic surveillance for clinical cases of acute encephalitis syndrome (AES), usually conducted nationwide. Case-based surveillance: with laboratory confirmation of cases of JE infection, usually conducted at sentinel sites.

Syndromic surveillance for AES Syndromic AES surveillance normally provides national data on the annual number of cases of acute encephalitis syndrome. A case definition must be used to ensure consistency in reporting across the country.

Clinical case definition for AES The WHO case definition for AES is: A person of any age, at any time of year with the acute onset of fever and one or both of: A change in mental status (including symptoms such as confusion, disorientation, coma, or inability to talk). New onset of seizures (excluding simple febrile seizures*). * Simple febrile seizure = a seizure in a child aged 6 months to less than 6 years old, whose only finding is fever and a single generalized convulsion lasting less than 15 minutes, and who recovers consciousness within 60 minutes of the seizure.

Case-based surveillance at sentinel sites AES surveillance identifies cases of acute encephalitis, but JE is clinically indistinguishable from other causes of AES. Therefore, among AES patients, laboratory testing is needed to confirm JE infection. If it is not feasible to conduct laboratory testing on every AES case, selected sites can be used to conduct sentinel surveillance.

Laboratory criteria for confirmation For surveillance purposes, the recommended method for laboratory confirmation of a JE virus infection is an IgM capture ELISA. Definition of a confirmed JE case: — Presence of JE virus-specific IgM antibody in a sample of cerebrospinal fluid (CSF) or serum.

Additional laboratory criteria Other laboratory confirmatory tests, not usually done for routine surveillance purposes, include Detection of JE virus antigens in brain tissue by immunohistochemistry or immunofluorescence. Detection of JE virus genome in CSF, serum, plasma, blood, or brain tissue by reverse transcriptase polymerase chain reaction or equivalent nucleic acid amplification test. Isolation of JE virus in CSF, serum, plasma, blood, or brain tissue. Detection of a four-fold or greater rise in JE virus-specific antibody as measured by haemagglutination inhibition or plaque reduction neutralization assay in serum collected during the acute and convalescent phase of illness.

Notes on laboratory testing A patient may present with AES due to another cause but have JE virus-specific IgM antibody present in serum. Therefore testing of a CSF sample is recommended whenever possible. Testing a single serum sample for JE IgM may not be diagnostic for persons vaccinated with JE vaccine within six months of illness onset as IgM in serum may be vaccine-related, not disease- related. In this situation: — Collection of a CSF specimen is essential. — Confirmation of diagnosis requires demonstration of JE IgM in CSF, JE virus isolation, positive PCR, immunohistochemistry or 4-fold rise in antibody titer.

Use of sentinel surveillance data The proportion of JE cases among AES cases can be determined at sentinel sites. This proportion can be used to extrapolate, using national AES data, a national estimate of JE incidence. Note – this assumes: — The sentinel site populations are representative of larger geographical areas. — The sentinel sites are functioning with reliable completeness and accuracy.

Case classification AES cases should be classified in one of the following four ways (see next slide for schematic): Laboratory-confirmed JE: An AES case that has been laboratory-confirmed as JE. Probable JE: An AES case that occurs in close geographic and temporal relationship to a laboratory-confirmed case of JE, in the context of an outbreak. AES – other agent: An AES case in which diagnostic testing is performed and an etiological agent other than JE virus is identified. AES – unknown: An AES case in which no diagnostic testing is performed or in which testing was performed but no etiological agent was identified or in which the test results were indeterminate.

Classification scheme for AES

Data collection Data to be collected include: Unique identifier. Age, sex. Place of residence. Travel history over the past 2 weeks. Immunization history. Date of onset of first symptoms. Symptoms (fever, change in mental status, seizures). Date samples collected. Clinical diagnosis. CSF and serum IgM results. Status at discharge (alive, dead, unknown). Date of death or discharge. Example of a case report form for data collection.

IndicatorTarget Completeness of monthly reporting> 90% Timeliness of monthly reporting> 80% Percentage of serum samples taken a minimum of 10 days after onset > 80% Performance indicators (1) Standard performance indicators should be monitored as a part of supervision to identify weaknesses in the system so that corrective action can be taken. WHO-suggested targets for countries with established surveillance systems:

Performance indicators (2) AES cases can be caused by many different infections, and they are expected to occur even if there is no JE. WHO defines a minimum AES rate as >5/100,000; i.e., even in the absence of JE, more than 5 AES cases per 100,000 population should be reported annually. This “minimum AES rate” should be used to indicate the surveillance system is functioning adequately.

Notes on JE surveillance (1) Reporting should be “zero-reporting,” i.e., no blanks should be left in the reporting forms; a zero should be indicated when there are no cases detected.

Notes on surveillance (2) Even in areas where laboratory diagnosis is not possible, syndromic surveillance is still very important—AES data frequently parallel trends in JE infection.

Feedback from surveillance data Feedback will be provided by: Monthly bulletins. Annual report. Annual meeting.

JE surveillance: summary Poor surveillance has precluded accurate assessment of the public health disease burden due to JE in some endemic Asian countries. Opportunities to enhance surveillance and new JE diagnostics will enable countries to take important decisions on control of JE disease.

Acknowledgements Please include the following acknowledgement if you use this slide set: This slide set was adapted from a slide set prepared by PATH’s Japanese encephalitis Project, based on the WHO-recommended Standards for Surveillance of Selected Vaccine-preventable Diseases (2003). For information: