Surveillance for polioviruses.

Clinical case-driven surveillance for poliovirus remains the cornerstone of monitoring the progress of the poliomyelitis eradication initiative (PEI). It includes notification and careful investigation of cases of acute flaccid paralysis (AFP), timely collection of stool specimens from the patient, and virological examination of the specimens in an accredited laboratory. Successful high quality APF surveillance requires painstaking perseverance and smooth interplay of several different groups of health care workers in a country. Environmental surveillance (ES) may in certain situations be more sensitive than AFP surveillance in detecting wild type poliovirus or vaccine derived poliovirus circulation. However, apart from being highly labour intensive, it cannot be optimally applied in large parts of the world because of the lack of converging sewage systems. Under these conditions, the very rationale of ES, examining of individual samples representing large groups (hundreds of thousands) of people cannot be readily exploited. Whatever approach of poliovirus surveillance is used, we will always be monitoring subgroups of potential poliovirus excreting people only. Therefore, several years long poliovirus-free monitoring period is needed to confirm that poliovirus transmission has stopped in a given population.