Data
management and analysis:
At
the end of each week, the DIO reports to the State EPI Officer
the line list of all new AFP cases reported during that week.
He summarizes the activities and reports the current status
of investigation and follow-up of AFP cases, including laboratory
results. Reporting takes place even when no cases of AFP were
identified; this serves as a check to ensure that reporting
has not simply been forgotten. The data are entered into the
NPSU database and are analyzed for program monitoring, checking
data quality and assessing progress toward eradication. Using
geographic information system (GIS) software, the NPSU data
management team maps the location of wild poliovirus cases in
the actual block and district where the case occurred, so that
appropriate programme action can be planned – specifically,
so that immunization activities can be planned, and to guide
surveillance officers in searching for additional cases in the
vicinity.
Case
classification:
As
soon as lab results and (when required) 60-day follow-up reports
are available, the cases are classified at NPSU as polio or
non-polio AFP. From 1997 through 1999, India followed the WHO
clinical classification system. According to this scheme, which
is applied in countries in which surveillance is not yet highly
developed, a case is classified as polio if wild poliovirus
is isolated from the stool specimen. If the case had inadequate
specimens and at 60-day follow-up is found to have residual
weakness, has died or has been lost to follow-up, then that
case is clinically classified as polio. The underlying rationale
for the clinical classification scheme is to err on the side
of diagnosing cases as polio. In an eradication programme, it
is important not to miss even a single case of polio; therefore,
unless laboratory results can definitely rule out polio, it
is safer to classify a case as “polio” if it has
clinical features suggestive of this diagnosis.
In
January 2000 India shifted to the more advanced and more specific
virologic system of case classification (see Virologic Classification
Scheme; countries may advance to this classification system
upon reaching a national non-polio AFP rate of at least 1 case/100,000
children aged <15 years; adequate stool collection from at
least 60% of AFP cases; all stools tested in a WHO-accredited
polio laboratory). This classification system is used in countries
that meet and sustain a high level of AFP surveillance performance,
as measured by specific indicators (see WHO Indicators of AFP
Surveillance and Laboratory Performance).* In India, use of
the virologic classification scheme has been possible due to
the achievement of high quality surveillance. Cases with inadequate
stool specimens and having residual weakness, who have died
or are lost to follow-up undergo additional investigation and
are presented for review by the National Expert Review Committee
(ERC), comprising highly skilled pediatricians, neurologists,
virologists and epidemiologists who examine all the evidence
and make a judgment on the most likely diagnosis. The ERC classifies
the case as “compatible with polio” or “discarded
as non-polio AFP.” Polio-compatible cases may be viewed
as evidence of a failure of surveillance, and serve as a reminder
that all efforts must be undertaken to ensure that adequate
stool specimens** are collected from every AFP case.
*Countries
may advance from Clinical Classification Scheme to Virologic
Classification Scheme when 1) non-polio AFP rate >1/100,000
children aged <15 years; 2) two adequate stool specimens
collected from >60% of AFP cases; 3) all specimens
processed in a WHO-accredited laboratory.
**Adequate
stool: two specimens collected within 14 days of paralysis onset
and at least 24 hours apart; each specimen must be of adequate
volume (8-10 grams) and arrive at a WHO-accredited laboratory
in good condition (i.e. no desiccation, no leakage, adequate
documentation and evidence that the cold chain was maintained).
