Case
and laboratory investigation
AFP
case investigation:
All
AFP cases are immediately investigated, usually within 48 hours
of notification, by a trained medical officer – usually
the DIO and/or the SMO. After confirming the case as AFP, the
investigator takes a detailed medical history, examines the
child and proceeds with the other aspects of case investigation.
The complete case investigation includes the history (including
details of immunization and travel), physical examination, collection
and transportation of stool specimens for laboratory testing,
search for additional cases and outbreak response investigation
(ORI) in the affected community, 60-day follow-up examination,
analysis of laboratory results and case classification. At all
steps of the investigation, standardized case investigation
forms are filled out, updated and completed so that laboratory
results can be linked to each case; all of these data are entered
into the computerized database at NPSU, where they are tracked
and analyzed.
Stool specimen collection and
transportation:
Collection
of stool specimens from every AFP case is a critical aspect
of the polio eradication strategy. Only by examination of the
child’s stool specimen in a WHO-accredited laboratory
can it be determined whether or not poliovirus is the cause
of the child’s paralysis. From every case of AFP, two
stool specimens are collected, and must be collected as soon
as possible after the onset of paralysis in the child –
ideally within 14 days of onset of paralysis and at least 24
hours apart. If poliovirus is present in the child, specimens
collected within 14 days are much more likely to yield the virus;
the probability of finding poliovirus in the stool diminishes
rapidly if stool is collected beyond the 14-day mark. Although
the optimal time period for detection of poliovirus in the stool
is within 14 days of paralysis onset, stool specimens should
be collected from any late-reported AFP case up to 60 days from
the date of paralysis onset. Beyond 60 days after paralysis
onset, the likelihood of detecting poliovirus is very low. Each
specimen should be 8 grams – each about the size of one
adult thumb – collected in a clean, dry, screw-capped
container. The container need not be sterile and no preservative/transport
media should be used. The specimens are collected, labeled and
then transported in the “cold chain” – on
frozen ice packs or ice, in a stool specimen carrier or a vaccine
carrier specifically designated for this purpose – to
one of India’s eight WHO-accredited polio laboratories.
A standard lab request form (LRF), which includes the unique
identification number that is assigned to each AFP case, is
also filled out by the investigator and accompanies the stool
specimen. The specimens undergo culture and further specialized
testing at the laboratory, and results are transmitted as rapidly
as possible to NPSU so that programme managers at national,
state and district level can plan the appropriate actions.
