Surveillance Indicators – GPEI
Surveillance Indicators

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)
The Global Polio Laboratory Network

Effective polio surveillance requires virologists, epidemiologists, clinicians and national immunization programme staff, backed up by a global network of laboratories.

The Global Polio Laboratory Network (GPLN) was established in 1990 by WHO and national governments. Its primary responsibility is to distinguish poliovirus as a cause of acute flaccid paralysis (AFP) from AFP caused by other diseases.

The GPLN consists of 146 WHO accredited polio laboratories, in 92 countries across the six WHO regions of the world.

National, regional and global specialized polio laboratories follow WHO-recommended procedures for detecting and characterizing polioviruses from stool and sewage samples collected from AFP cases and the environment, respectively.

The laboratories follow standardized protocols to (i) isolate poliovirus, (ii) identify wild poliovirus (WPV) or screen for Sabin (vaccine) poliovirus and vaccine-derived poliovirus (VDPV), and (iii) conduct genomic sequencing. Sequencing results help monitor how poliovirus is spreading by comparing the nucleotide sequences of poliovirus isolates.

The accuracy and quality of testing at GPLN member laboratories is monitored through an annual accreditation programme that includes onsite reviews of work practices, performance and proficiency testing.

The GPLN processes over 220 000 stool samples from AFP cases (and their contacts), and more than 8 000 sewage samples per year. In addition to surveillance, the GPLN carries out a research agenda aimed at improving laboratory diagnostics.

The GPLN meets every year to develop recommendations for improving performance and coordination and determine the research and resource needs of the network laboratories.