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Surveillance

Acute Flaccid Paralysis (AFP) surveillance

Nationwide AFP (acute flaccid paralysis) surveillance is the gold standard for detecting cases of poliomyelitis. The four steps of surveillance are:

  1. finding and reporting children with acute flaccid paralysis (AFP)
  2. transporting stool samples for analysis
  3. isolating and identifying poliovirus in the laboratory
  4. mapping the virus to determine the origin of the virus strain.

Environmental surveillance

Environmental surveillance involves testing sewage or other environmental samples for the presence of poliovirus. Environmental surveillance often confirms wild poliovirus infections in the absence of cases of paralysis. Systematic environmental sampling (e.g. in Egypt and Mumbai, India) provides important supplementary surveillance data. Ad-hoc environmental surveillance elsewhere (especially in polio-free regions) provides insights into the international spread of poliovirus.

Surveillance indicators

Indicator

Minimum levels for certification standard surveillance

Completeness of reporting 

At least 80% of expected routine (weekly or monthly) AFP surveillance reports should be received on time, including zero reports where no AFP cases are seen. The distribution of reporting sites should be representative of the geography and demography of the country

Sensitivity of surveillance

At least one case of non-polio AFP should be detected annually per 100 000 population aged less than 15 years. In endemic regions, to ensure even higher sensitivity, this rate should be two per 100 000.

Completeness of case investigation

All AFP cases should have a full clinical and virological investigation with at least 80% of AFP cases having ‘adequate’ stool specimens collected. ‘Adequate’ stool specimens are two stool specimens of sufficient quantity for laboratory analysis, collected at least 24 hours apart, within 14 days after the onset of paralysis, and arriving in the laboratory by reverse cold chain and with proper documentation.

Completeness of follow-up

At least 80% of AFP cases should have a follow-up examination for residual paralysis at 60 days after the onset of paralysis

Laboratory performance

All AFP case specimens must be processed in a WHO-accredited laboratory within the Global Polio Laboratory Network (GPLN)

Performance of AFP surveillance and incidence of poliomyelitis

Weekly Epidemiological Record