Divergence of wastewater SARS-CoV-2 and reported laboratory-confirmed COVID-19 incident case data coincident with wide-spread availability of at-home COVID-19 antigen tests (preprint)

Concentrations of SARS-CoV-2 RNA in wastewater settled solids from publicly owned treatment works (POTWs) historically correlated strongly with laboratory confirmed incident COVID-19 case data. With the increased availability of at-home antigen tests since late 2021 and early 2022, laboratory test availability and test seeking behavior has decreased. In the United States, the results from at-home antigen tests are not typically reportable to public health agencies and thus are not counted in case reports. As a result, the number of reported laboratory-confirmed incident COVID-19 cases has decreased dramatically, even during times of increased test positivity rates and wastewater concentrations of SARS-CoV-2 RNA. Herein, we tested whether the correlative relationship between wastewater concentrations of SARS-CoV-2 RNA and reported laboratory-confirmed COVID-19 incidence rate has changed since 1 May 2022, a point in time immediately before the onset of the BA.2/BA.5 surge, the first surge to begin after at-home antigen test availability was high in the region. We used daily data from three POTWs in the Greater San Francisco Bay Area of California, USA for the analysis. We found that although there is a significant positive association between wastewater measurements and incident rate data collected after 1 May 2022, the parameters describing the relationship are different than those describing the relationship between the data collected prior to 1 May 2022. If laboratory test seeking or availability continues to change, the relationship between wastewater and reported case data will continue to change. Results suggests that, assuming SARS-CoV-2 RNA shedding remains relatively stable among those infected with the virus as different variants emerge, that wastewater concentrations of SARS-CoV-2 RNA can be used to estimate COVID-19 cases as they would have been during the time when laboratory testing availability and test seeking behavior were at a high (here, before 1 May 2022) using the historical relationship between SARS-CoV-2 RNA and COVID-19 case data.

Wastewater surveillance of human influenza, metapneumovirus, parainfluenza, respiratory syncytial virus (RSV), rhinovirus, and seasonal coronaviruses during the COVID-19 pandemic (preprint)

Background: Respiratory disease is a major cause of morbidity and mortality; however, current surveillance for circulating respiratory viruses is passive and biased. Seasonal circulation of respiratory viruses changed dramatically during the COVID-19 pandemic. More active methods for understanding respiratory disease dynamics are needed to better inform public health response and to guide clinical decision making. Wastewater-based epidemiology has been used to understand COVID-19, influenza A, and RSV infection rates at a community level, but has not been used to investigate other respiratory viruses. Methods: We measured concentrations of influenza A and B, RSV A and B, human parainfluenza (1-4), rhinovirus, seasonal human coronaviruses, and human metapneumovirus RNA in wastewater solids three times per week for 17 months spanning the COVID-19 pandemic at a wastewater treatment plant in California, USA. Novel probe-based assays were developed and validated for non-influenza viral targets. We compared viral concentrations to positivity rates for viral infections from clinical specimens submitted to sentinel laboratories. Findings: We detected RNA from all target viruses in wastewater solids. Human rhinovirus and seasonal coronaviruses were found at highest concentrations. Concentrations of viruses correlated significantly and positively with positivity rates of associated viral diseases from sentinel laboratories. Measurements from wastewater indicated limited circulation of RSV A and influenza B, and human coronavirus OC43 dominated the seasonal human coronavirus infections while human parainfluenza 1 and 4A dominated among parainfluenza infections. Interpretation: Wastewater-based epidemiology can be used to obtain information on circulation of respiratory viruses at a community level without the need to test many individuals because a single sample of wastewater represents the entire contributing community. Results from wastewater can be available within 24 hours of sample collection, allowing real time information to inform public health response, clinical decision making, and individual behavior modifications.

Regional replacement of SARS-CoV-2 variant BA.1 with BA.2 as observed through wastewater surveillance (preprint)

An understanding of circulating SARS-CoV-2 variants can inform pandemic response, vaccine development, disease epidemiology, and use of monoclonal antibody treatments. We developed custom assays targeting characteristic mutations in SARS-CoV-2 variants Omicron BA.1 and BA.2 and confirmed their sensitivity and specificity in silico and in vitro. We then applied these assays to daily wastewater solids samples from eight publicly owned treatment works in the greater Bay Area of California, USA, over four months to obtain a spatially and temporally intensive data set. We documented regional replacement of BA.1 with BA.2 in agreement with, and ahead of, clinical sequencing data. This study highlights the utility of wastewater surveillance for real time tracking of SARS-CoV-2 variant circulation. SynopsisWastewater surveillance was used to document regional emergence of SARS-CoV-2 variant Omicron BA.2 ahead of clinical surveillance. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=103 SRC="FIGDIR/small/22274160v2_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@10e4406org.highwire.dtl.DTLVardef@1941dd9org.highwire.dtl.DTLVardef@133b438org.highwire.dtl.DTLVardef@17ce1c4_HPS_FORMAT_FIGEXP M_FIG C_FIG

Effect of SARS-CoV-2 digital droplet RT-PCR assay sensitivity on COVID-19 wastewater based epidemiology (preprint)

We developed and implemented a framework for examining how molecular assay sensitivity for a viral RNA genome target affects its utility for wastewater-based epidemiology. We applied this framework to digital droplet RT-PCR measurements of SARS-CoV-2 and Pepper Mild Mottle Virus genes made using 10 replicate wells, and determined how using fewer wells affected assay sensitivity and its performance for wastewater-based epidemiology applications. We used a computational, downsampling approach. When percent of positive droplets was between 0.024% and 0.5% (as was the case for SARS-CoV-2 genes during the Delta surge), measurements obtained with 3 or more wells were similar to those obtained using 10. When percent of positive droplets was less than 0.024%, then 6 or more wells were needed to obtain similar results as those obtained using 10 wells. When COVID-19 incidence is low, as it was before the Delta surge and SARS-CoV-2 gene concentrations are <104 cp/g, using 6 wells will yield a detectable concentration 90% of the time. Overall, results support an adaptive approach where assay sensitivity is increased by running 6 or more wells during periods of low SARS-CoV-2 gene concentrations, and 3 or more wells during periods of high SARS-CoV-2 gene concentrations.

SARS-CoV-2 RNA wastewater settled solids surveillance frequency and impact on predicted COVID-19 incidence using a distributed lag model (preprint)

SARS-CoV-2 RNA concentrations in wastewater settled solids correlate well with COVID-19 incidence rates (IRs). Here, we develop distributed lag models (DLMs) to estimate IRs using concentrations of SARS-CoV-2 RNA from wastewater solids and investigate the impact of sampling frequency on model performance. SARS-CoV-2 N gene and PMMoV RNA concentrations were measured daily at four wastewater treatment plants in California. Artificially reduced datasets were produced for each plant with sampling frequencies of once every 2, 3, 4, and 7 days. Sewershed-specific models that related daily N/PMMoV to IR were fit for each sampling frequency with data from mid-Nov 2020 through mid-July 2021, which included the period of time during which Delta emerged. Models were used to predict IRs during a subsequent out-of-sample time period. When sampling occurred at least once every 4 days, the in- and out-of-sample root mean square error (RMSE) changed less than 7 cases/100,000 compared to daily sampling across sewersheds. This work illustrates that real-time, daily predictions of IR are possible with small error, despite changes in circulating variants, when sampling frequency is once every 4 days or more. However, reduced sampling frequency may not serve other important wastewater surveillance use cases.

Detection of SARS-CoV-2 variant Mu, Beta, Gamma, Lambda, Delta, Alpha, and Omicron in wastewater settled solids using mutation-specific assays is associated with regional detection of variants in clinical samples (preprint)

Changes in the circulation of SARS-CoV-2 variants of concern (VOCs) may require changes in public health response to the COVID-19 pandemic, as they have the potential to evade vaccines and pharmaceutical interventions and may be more transmissive relative to other SARS-CoV-2 variants. As such, it is essential to track and prevent their spread in susceptible communities. We developed digital RT-PCR assays for mutations characteristic of VOCs and used them to quantify those mutations in wastewater settled solids samples collected from a publicly owned treatment works (POTW) during different phases of the COVID-19 pandemic. Wastewater concentrations of single mutations characteristic to each VOC, normalized by the concentration of a conserved SARS-CoV-2 N gene, correlate to regional estimates of the proportion of clinical infections caused by each VOC. These results suggest targeted RT-PCR assays can be used to detect variants circulating in communities and inform public health response to the pandemic.

Respiratory Syncytial Virus (RSV) RNA in wastewater settled solids reflects RSV clinical positivity rates (preprint)

Wastewater based epidemiology (WBE) uses concentrations of infectious agent targets in wastewater to infer infection trends in the contributing community. To date, WBE has been used to gain insight into infection trends of gastrointestinal diseases, but its application to respiratory diseases has been limited to COVID-19. Here we report Respiratory Syncytial Virus (RSV) genomic RNA can be detected in wastewater settled solids at two publicly owned treatment works (POTWs). We further show that its concentration in settled solids is strongly associated with clinical positivity rates for RSV at sentinel laboratories across the state in 2021, a year with anomalous seasonal trends in RSV disease. Given that RSV infections have similar clinical presentations to COVID-19, can be life threatening for some, and immunoprophylaxis distribution for vulnerable people is based on outbreak identification, WBE represents an important tool to augment current RSV surveillance and public health response efforts. Graphical Abstract Synopsis Respiratory Syncytial Virus RNA concentrations in settled solids from wastewater treatment plants are associated with state-wide RSV clinical positivity rates.

Estimating relative abundance of two SARS-CoV-2 variants through wastewater surveillance at two large metropolitan sites (preprint)

Monitoring SARS-CoV-2 variants of concern (VOCs) is critical for public health management of COVID-19. Case isolate sequencing is resource-intensive and not all isolates can be sequenced, and thus are not representative. However, since wastewater SARS-CoV-2 RNA concentrations correlate with COVID-19 case incidence in sewersheds, tracking VOCs through wastewater is appealing. We developed targeted digital RT-PCR assays to monitor abundance of select mutations in Alpha and Delta VOCs in wastewater settled solids, applied these to July 2020-August 2021 samples from two large metropolitan sewersheds, and compared results to estimates of variant abundance from case isolate sequencing. Wastewater measurements tracked closely with case isolate estimates at each site (rp= 0.82, 0.88 for Alpha and rp= 0.97 for Delta). Mutations were detected in wastewater measurements even at levels <5% of circulating virus and in samples available weeks before case isolate results. Therefore, wastewater variant monitoring should be strategically deployed to complement case isolate sequencing.

SARS-CoV-2 RNA is enriched by orders of magnitude in solid relative to liquid wastewater at publicly owned treatment works (preprint)

Wastewater-based epidemiology has gained attention throughout the world for detection of SARS-CoV-2 RNA in wastewater to supplement clinical testing. Methods have been developed using both the liquid and the solid fraction of wastewater, with some studies reporting higher concentrations in solids. To investigate this relationship further, we collaborated with six other laboratories to conduct a study across five publicly owned treatment works (POTWs) where both primary solids and raw wastewater influent samples were collected and quantified for SARS-CoV-2 RNA. Solids and influent samples were processed by participating laboratories using their respective methods and retrospectively paired based on date of collection. SARS-CoV-2 RNA concentrations by mass (gene copies per gram) were higher in solids than in influent by approximately three orders of magnitude. Concentrations in matched solids and influent were positively and significantly correlated at all five POTWs. RNA concentrations in both solids and influent were correlated to COVID-19 incidence rates in the sewershed and thus representative of disease burden; the solids methods appeared to produce a comparable relationship between SARS-CoV-2 RNA concentration measurements and incidence rates across all POTWs. Solids and influent methods showed comparable sensitivity, N gene detection frequency, and calculated empirical incidence rate lower limits. Analysis of solids has the advantage of using less sample volume to achieve similar sensitivity to influent methods.

High frequency, high throughput quantification of SARS-CoV-2 RNA in wastewater settled solids at eight publicly owned treatment works in Northern California shows strong association with COVID-19 incidence (preprint)

A number of recent retrospective studies have demonstrated that SARS-CoV-2 RNA concentrations in wastewater are associated with COVID-19 cases in the corresponding sewersheds. Implementing high-resolution, prospective efforts across multiple plants depends on sensitive measurements that are representative of COVID-19 cases, scalable for high throughput analysis, and comparable across laboratories. We conducted a prospective study across eight publicly owned treatment works (POTWs). A focus on SARS-CoV-2 RNA in solids enabled us to scale-up our measurements with a commercial lab partner. Samples were collected daily and results were posted to a website within 24-hours. SARS-CoV-2 RNA in daily samples correlated to incidence COVID-19 cases in the sewersheds; a 1 log 10 increase in SARS-CoV-2 RNA in settled solids corresponds to a 0.58 log 10 (4X) increase in sewershed incidence rate. SARS-CoV-2 RNA signals measured with the commercial laboratory partner were comparable across plants and to measurements conducted in a university laboratory when normalized by pepper mild mottle virus PMMoV RNA. Results suggest that SARS-CoV-2 RNA should be detectable in settled solids for COVID-19 incidence rates > 1/100,000 (range 0.8 - 2.3 cases per 100,000). These sensitive, representative, scalable, and comparable methods will be valuable for future efforts to scale-up wastewater-based epidemiology. Importance Access to reliable, rapid monitoring data is critical to guide response to an infectious disease outbreak. For pathogens that are shed in feces or urine, monitoring wastewater can provide a cost-effective snapshot of transmission in an entire community via a single sample. In order for a method to be useful for ongoing COVID-19 monitoring, it should be sensitive for detection of low concentrations of SARS-CoV-2, representative of incidence rates in the community, scalable to generate data quickly, and comparable across laboratories. This paper presents a method utilizing wastewater solids to meet these goals, producing measurements of SARS-CoV-2 RNA strongly associated with COVID-19 cases in the sewershed of a publicly owned treatment work. Results, provided within 24 hrs, can be used to detect incidence rates as low as approximately 1/100,000 cases and can be normalized for comparison across locations generating data using different methods.

Effect of storage conditions on SARS-CoV-2 RNA quantification in wastewater solids (preprint)

SARS-CoV-2 RNA in wastewater settled solids is associated with COVID-19 incidence in sewersheds and therefore, there is a strong interest in using these measurements to augment traditional disease surveillance methods. A wastewater surveillance program should provide rapid turn around for sample measurements (ideally within 24 hours), but storage of samples is necessary for a variety of reasons including biobanking. Here we investigate how storage of wastewater solids at 4{degrees}C, -20{degrees}C, and -80{degrees}C affects measured concentrations of SARS-CoV-2 RNA. We find that short term (7-8 d) storage of raw solids at 4{degrees}C has little effect on measured concentrations of SARS-CoV-2 RNA, whereas longer term storage at 4{degrees}C (35-122 d) or freezing reduces measurements by 60%, on average. We show that normalizing SARS-CoV-2 RNA concentrations by concentrations of pepper mild mottle virus (PMMoV) RNA, an endogenous wastewater virus, can correct for changes during storage as storage can have a similar effect on PMMoV RNA as on SARS-CoV-2 RNA. The reductions in SARS-CoV-2 RNA in solids during freeze thaws is less than those reported for the same target in liquid influent by several authors.