West Nile Virus (Orthoflavivirus nilense) RNA concentrations in wastewater solids at five wastewater treatment plants in the United States

Abstract

Background: Orthoflavivirus nilense, formerly known as West Nile Virus (WNV), has become endemic to the United States since its introduction in 1999. Current surveillance methods rely primarily on mosquito pool testing, which is both costly and time-intensive. Wastewater-based epidemiology (WBE) has proven an effective method for the surveillance of various pathogens, including other orthoflaviviruses such as Dengue. WBE for WNV represents a potentially valuable surveillance approach that has so far been underexplored.

Methods: A targeted droplet digital reverse transcription-polymerase chain reaction (RT-PCR) approach (ddRT-PCR) was used to measure WNV concentrations in wastewater retrospectively from five locations and in over 600 samples. Three of these locations were in communities with multiple confirmed WNV infections, while two were not. Samples were collected during periods corresponding to typical WNV seasonality (spring to fall). SARS-CoV-2 RNA was measured simultaneously to assess nucleic acid degradation during sample storage. Publicly available confirmed WNV case data were compiled from the California and Nebraska departments of public health and their weekly arboviral reports.

Results: WNV RNA was detected in wastewater samples during periods of known viral circulation within a community. The adopted ddRT-PCR assay is highly specific and sensitive, and detections in wastewater solids correspond to the occurrence of cases in the season and location of sampling. WNV was detected in nine samples in three locations with known WNV clinical cases-wastewater positivity rates in these locations ranged from 3.3% to 13%. The results suggest that wastewater monitoring could serve as an effective complement to traditional surveillance methods, particularly for sentinel surveillance in locations which do not have extensive mosquito and clinical testing systems.

Keywords: Wasteater-based epidemiology; Wastewater; West Nile Virus.

Figure 1. Map of the wastewater treatment plants (WWTPs) enrolled in this study.

The orange dots represent the location of the five WWTPs and states with participating WWTPs are shaded in dark gray. Generated using ArcGIS desktop; map layer from The United States Census Bureau’s Cartographic Boundary Files (https://www.census.gov/geographies/mapping-files/time-series/geo/carto-boundary-file.html).

Figure 2. WNV RNA and case data used in the study.

Concentrations of WNV RNA measured at SAC, NE, and WD sites during the study (in red, left axis) and confirmed cases of WNV infection in the associated county (SAC and WD) or state (NE) (in black, open circles, right axis). Error bars on the WNV RNA measurements represent standard deviations. A 0 value for concentration was imputed for samples where WNV RNA was not detected.

Figure 3. WNV incidence rate as a function of wastewater positivity rate.

Data is for the five sites over the time periods included for each in this study. The points representing SJ and OSP are on top of each other near the origin. Kendall’s tau and associated p value are provided.