ABSTRACT
Auckland is New Zealand's largest city and is the main international entry point to New Zealand, with most of the nation's Managed Isolation and Quarantine Facilities. Consequently, it is the place most likely for a COVID-19 outbreak to occur and, accordingly, has been the focus of efforts to monitor SARS-CoV-2 via wastewater-based epidemiology. Historically, wastewater-based epidemiology has mainly been applied at the catchment or sewershed scale, with samples collected at wastewater treatment plants. COVID-19 has necessitated a re-evaluation of this broad-scale approach to wastewaterbased epidemiology in New Zealand, where there is a need for more detailed information to better target the public health response. Using Auckland as a case study, this paper assesses the spatial and temporal extent of the city's wastewater network to inform the selection of strategic neighbourhoodscale sampling sites for wastewater-based epidemiology. Sample site selection criteria included topology and connectivity of the sewer network, the capacity to record sewer flow, limited rain infiltration, resident population, and accessibility. Six sites were identified that provide an immediate opportunity for neighbourhood-scale monitoring. Reflecting on the analysis required for selecting appropriate monitoring locations, the paper moves to critically discuss the key unknowns and research needs associated with conducting neighbourhoodscale wastewater-based epidemiology. Population mobility poses challenges for estimating population size and for capturing a positive SARS-CoV-2 signal in wastewater at this scale. There is a need to determine the full spectrum of residence times within the sewer network to design representative sampling and the implications of disregarding residence times in the current sampling regimes are poorly understood. Hydraulic models require refinement to accurately account for variable residence times and topological features in the network (e.g., holding tanks and pumping stations). Addressing these challenges is urgent and ongoing to realise the benefits of neighbourhood-scale wastewater-based epidemiology in response to COVID-19 and beyond.