Surveillance is key to polio eradication as it indicates where the poliovirus is circulating and who is being affected. Stopping every poliovirus transmission chain in a timely manner is the main objective of the
Polio Eradication Programme in Pakistan. As the sensitivity of the surveillance system continuous to be enhanced, detection is improving and more virus is being revealed. This is helping the programme respond to outbreaks quickly and appropriately.
Acute Flaccid Paralysis Surveillance
Acute Flaccid Paralysis (AFP) is defined as either “any case with recent or sudden onset of floppy paralysis or muscle weakness in a child aged less than 15 years of age, due to any cause; or "any paralytic illness in a person of any age in whom a clinician suspects polio”.
AFP surveillance is one of the four cornerstone strategies of polio eradication which seeks to identify all cases of polio through a system that targets any case of acute flaccid paralysis as a potential case of polio.
In Pakistan, AFP surveillance began in 1997, but was given focused attention in 2000. Currently, Pakistan has a well-functioning and sensitive AFP surveillance system at national, provincial, and district levels.
AFP Surveillance is conducted through direct reporting by clinicians or the community. Active surveillance is carried out through weekly visits of priority facilities or other formal or informal healthcare services providers, and passive surveillance is conducted through weekly “zero reporting” by primary healthcare providers. The system operates as outlined by the National AFP Surveillance Plan. Frequent field reviews are carried out to ensure high quality is maintained.
The best available method to confirm the diagnosis of poliomyelitis is the isolation and identification of poliovirus from the stool. The World Health Organization (WHO) has developed a global network of laboratories to provide this service in collaboration with several other institutions. The virology laboratory at NIH Islamabad is the Regional Reference Laboratory (RRL) for polio eradication and continues to demonstrate very high standards of quality control and meets the international targets for accuracy. All stool specimens collected from reported AFP cases are tested at the RRL. In order to determine transmission dynamics within the population, genomic sequencing is performed for all poliovirus isolates, which determines genetic relationship to previously detected viruses.
The RRL will also play a key role in certification of polio eradication by verifying the absence of wild poliovirus circulation.
In addition to AFP surveillance, environmental surveillance helps enhance the sensitivity of surveillance for polioviruses. Environmental surveillance involves testing sewage or other environmental samples for the presence of poliovirus. In Pakistan, the programme has used environmental surveillance to detect poliovirus in sewage in strategic locations since 2009.
In the past couple of years, the number of sites for environmental surveillance has been increased and currently, there are 53 sampling sites designated in a total of 33 districts / towns of the country.
While the environmental surveillance system in Pakistan is being enhanced, positive environmental samples have halved in 2016 compared to 2015 which indicates an overall decrease in intensity of transmission across the country.
Stool Surveys among healthy children
The program conducts periodic stool surveys among the children from high risk populations which may be carrying poliovirus without any paralytic cases or circulation may otherwise difficult to detect through regular AFP surveillance.