Transcript Document

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 WHOrecommended 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 diseaserelated. 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.
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:
Indicator
Completeness of monthly reporting
Target
> 90%
Timeliness of monthly reporting
> 80%
Percentage of serum samples taken
a minimum of 10 days after onset
> 80%
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: www.path.org/je