Sporadic isolation of Sabin-like polioviruses and high detection of non-polio enteroviruses during sewage surveillance in seven Italian cities, after several years of inactivated polio vaccination.

Sewage surveillance in seven Italian cities between 2005-2008, after IPV introduction in 2002, showed rare polioviruses, none wild-type or cVDPV, and many other enteroviruses among 1,392 samples analyzed. Two of five polioviruses (PV) detected were Sabin-like PV2 and three PV3, based on ELISA and PCR. Neurovirulence-related mutations were found in the 5'NCR of all strains, and for a PV2 also in the VP1 region 143 (Ile>Thr). Intertypic recombination in the 3D region was detected in a second PV2 (Sabin2/Sabin1) and a PV3 (Sabin3/Sabin2). The low mutation rate in VP1 for all PVs suggests limited inter-human virus passages, consistent with efficient polio immunization in Italy. Nonetheless, these findings highlight the risk of wild or Sabin polio reintroduction from abroad. Non-polio-enteroviruses (NPEVs) were detected, of which 448 were Coxsackievirus B (CVB) and 294 Echoviruses (Echo). Fifty-six NPEVs failing serological typing were characterized by sequencing the VP1 region (nt 2628-2976). Four-hundred forty-eight CVB and two-hundred ninety-four Echo strains were identified, among which CVB2, CVB5 and Echo11 predominated. Environmental CVB5 and CVB2 strains from this study showed high sequence identity with GenBank global strains. The high similarity between environmental NPEVs and clinical strains from the same areas of Italy and periods indicates that environmental strains reflect the viruses circulating in the population and highlights the potential risk of inefficient wastewater treatments. This study confirms that sewage surveillance can be more sensitive than AFP surveillance in monitoring silent poliovirus circulation in the population, and the suitability of molecular approaches to enterovirus typing.