Community surveillance after detection of poliovirus in the environment in London, United Kingdom, October 2022 to April 2023

Background: Vaccine-derived polioviruses (VDPVs) continue to circulate internationally, causing sporadic cases and outbreaks of paralytic polio in countries certified as polio-free. In 2022, sustained detection of type 2 VDPVs was reported in environmental surveillance samples collected from London. Genetic mutations indicative of loss of attenuation of virulence were observed, consistent with community transmission events over several months. Aim: We aimed to determine the extent of geographical spread of transmission in an area of environmental poliovirus detection. Methods: We implemented an opportunistic, cross-sectional survey in areas where environmental surveillance indicated sustained VDPV transmission between October 2022 and April 2023. Residual stool samples taken from children<16 years presenting to primary or secondary healthcare were examined for enteroviruses, including poliovirus. Methods for poliovirus detection recommended by the World Health Organization, including virus isolation in cell culture, PCR and molecular characterisation, were applied to residual stool material on a daily basis with real-time clinical reporting. Results: We examined 1,251 stool samples from 1,051 children presenting to healthcare with illness over a 6-month period. A range of enteroviruses from groups A, B and C were found, but no poliovirus was detected. Documented polio vaccination coverage was high, between 95% and 98% in under 5-year-olds. Conclusion: Poliovirus was not widespread in the area of environmental poliovirus isolation. Opportunistic poliovirus testing of residual stool samples taken from children seeking healthcare was feasible and can be implemented rapidly in areas where poliovirus circulation is suspected, although untargeted sampling may not adequately capture populations at highest risk.