Surveillance is key to poliomyelitis (polio) eradication as it indicates where the polio virus is circulating and who is being affected. Surveillance is used to verify the success of polio eradication efforts. Surveillance is conducted for acute flaccid paralysis, which is the main symptom of polio.
Other diseases can also cause acute flaccid paralysis. They occur at a rate of approximately 1 per 100 000 children under 15. If surveillance is able to detect these cases then it is also able to detect polio cases.
All public and private health facilities which see such cases are expected to report promptly through the designated health care system. Epidemiologic information is collected on every case and two adequate stool samples 24 hours apart should be collected within 14 days of onset of paralysis and sent under optimal temperature to a virology laboratory to test for the presence of polio viruses. Polio viruses are then studied to differentiate between wild viruses that cause disease and vaccine viruses. Wild viruses are isolated and then genetically mapped in specialized laboratories to determine their origin.
Supplementary surveillance activities include searching for the wild virus in samples collected from sewage, as in in Egypt and Pakistan. This system is particularly helpful in alerting authorities of circulating wild viruses when there are no reported cases of polio and in confirming that circulation has been interrupted.
Surveillance indictors have been adopted globally to assess the sensitivity of the surveillance system and its completeness.
In non-endemic areas the minimum level is to detect one non-polio case of acute flaccid paralysis per 100 000 children under 15. In endemic areas, this level should be 2 per 100 000.
For reporting, at least 80% of routine reporting is received and 80% of active surveillance visits conducted.
At least 80% of acute flaccid paralysis cases have two adequate stool specimens collected and processed in a WHO-accredited laboratory.
At least 80% of acute flaccid paralysis cases are examined after 60 days of onset of paralysis for evidence of residual paralysis.