Feasibility of quantitative environmental surveillance in poliovirus eradication strategies

The progress of the Global Polio Eradication Initiative is monitored by acute flaccid paralysis (AFP) surveillance supplemented with environmental surveillance in selected areas. To assess the sensitivity of environmental surveillance, stools from (re)vaccinated elderly persons with a low seroprevalence and from wastewater were concurrently collected and analyzed in the Netherlands over a prolonged period of time. A total number of 228 healthy individuals with different levels of immunity were challenged with monovalent oral polio vaccine serotype 1 or 3. Poliovirus concentrations were determined by the titration of fecal suspensions on poliovirus-sensitive L20B cells and of sewage concentrates by L20B monolayer plaque assay. Almost half of the individuals (45%) shed poliovirus on day 3 after challenge, which peaked (57%) on day 8 with an average poliovirus excretion of 1.3 × 10(5) TCID(50) per g of feces and gradually decreased to less than 5% on day 42. The virus concentrations in sewage peaked on days 6 to 8 at approximately 100 PFU per liter, remained high until day 14, and subsequently decreased to less than 10 PFU per liter on day 29. The estimated poliovirus concentration in sewage approximated the measured initial virus excretion in feces, within 1 log(10) variation, resulting in a sensitivity of detection of 100 infected but mostly asymptomatic individuals in tens of thousands of individuals. An additional second peak observed in sewage may indicate secondary transmission missed by enterovirus or AFP surveillance in patients. This enables the detection of circulating poliovirus by environmental surveillance, supporting its feasibility as an early warning system.