Environmental surveillance of poliovirus and non-polio Enterovirus in Milan (Northern Italy) in 2011 and 2012

Introduction. The WHO Strategic Plan of the Global Polio Eradication Initiative indicates the environmental surveillance of poliovirus (PV) as a key activity to supplement the standard acute flaccid paralysis (AFP) surveillance. In this framework, other human Enteroviruses (EVs) are monitored due to their high circulation in human population and their involvement in outbreaks of meningitis, encephalitis, hand-foot-mouth disease and other acute and chronic manifestations. This study aimed at analyzing the circulation of PVs (wild, Sabin-like, and vaccine-derived) and non-polio Enteroviruses (NPEVs) in wastewater samples collected in the Milan area (Northern Italy) in 2011 and 2012. Methods. This study was carried out according to WHO guidelines for environmental surveillance of PV (WHO/V&B/03.03). Wastewater samples were collected regularly twice a month at the inlet of 3 different wastewater treatment plants in the Milan area in 2011 and 2012. EV identification was carried out by viral isolation in cell cultures (RD and L20b), followed by PCR specific for the 5\u2032 noncoding region (5\u2032NCR) (nt. 179-575) common to all EVs. EV characterization was performed by sequence analysis of the VP1 region (nt. 2628-2976). Result. Overall, 128 sewage samples were collected during the study period. No PVs were isolated. NPEVs were isolated in 70% and 76.5% of wastewater specimens analyzed in 2011 and 2012, respectively. All isolates belonged to the EV-B group and those circulating more intensely were Echovirus type 11 (48.8% in 2011; 65.4% in 2012) and Echovirus type 6 (34.8% in 2011; 13.5% in 2012), representing 81% of all EVs identified. The circulation of Echovirus type 11 significantly (p