Exploring trends in SARS-CoV-2 RNA concentrations in wastewater

Exploring trends in SARS-CoV-2 RNA concentrations in wastewater

In a latest research posted to medRxiv* preprint server, researchers characterised developments of extreme acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA ranges in wastewater.

Study: Identifying trends in SARS-CoV-2 RNA in wastewater to infer changing COVID-19 incidence: Effect of sampling frequency. Image Credit: DedMityay/Shutterstock
Examine: Figuring out developments in SARS-CoV-2 RNA in wastewater to deduce altering COVID-19 incidence: Impact of sampling frequency. Picture Credit score: DedMityay/Shutterstock

Wastewater-based epidemiology (WBE) depends on infectious illness marker ranges within the wastewater to evaluate illness incidence in the neighborhood. The coronavirus illness 2019 (COVID-19) pandemic has elevated consideration to WBE. Particularly, SARS-CoV-2 RNA concentrations in wastewater-settled solids correlate effectively with incident scientific COVID-19 instances (lab-confirmed instances) in the identical sewer shed.

Moreover, developments in wastewater SARS-CoV-2 RNA concentrations precede these in incident COVID-19 instances in communities. Nonetheless, there’s uncertainty in deciphering and utilizing WBE information to assist decision-making. Additional, there have been restricted efforts relating to tips on how to monitor developments actively. Regular pattern measures, equivalent to charges of change, easy transferring averages, et cetera., present much less consideration to pattern stability and statistical significance and might typically be complicated/deceptive.

Concerning the research

Within the current research, researchers used every day measurements of SARS-CoV-2 RNA in wastewater to check three pattern evaluation strategies and consider their efficiency. Every day sampling from the San José-Santa Clara regional wastewater facility commenced on November 15, 2020, till September 15, 2022. The authors used information on SARS-CoV-2 nucleocapsid (N) gene concentrations in gene copies/g of dry weight normalized by pepper delicate mottle virus (PMMoV) concentrations.

Three analytic metrics – % change (PC), Mann-Kendall (MK) pattern take a look at, and relative energy index (RSI), had been used to establish developments in N or PMMoV over time. RSI is helpful to tell pattern stability, whereas the opposite two inform about statistical significance. The RSI was calculated for the seven-day right-aligned transferring common of N or PMMoV utilizing a 14-day look-back interval.

For PC, the authors used the formulation that the USA Facilities for Illness Management and Prevention (CDC) makes use of for computing developments within the wastewater SARS-CoV-2 RNA concentrations. The MK pattern take a look at, a non-parametric take a look at, was used to judge monotonic developments in a time-series dataset. The MK pattern take a look at was utilized to check uncooked N or PMMoV information utilizing a 14-day look-back interval.

Heatmaps had been created for the whole evaluation interval and individually for 3 COVID-19 waves attributable to 1) SARS-CoV-2 Delta, 2) Omicron BA.1, and three) Omicron BA.2 and BA.5 variants. Additional, the authors down-sampled the dataset to repeat PC and MK pattern take a look at strategies. The down-sampled dataset was generated for all mixtures overlaying frequencies between two samples/week and 6 samples/week.

Wastewater SARS-CoV-2 RNA developments had been stratified as growing, lowering, or steady utilizing the three metrics. Furthermore, the MK pattern take a look at and PC calculated the upward and downward sensitivity and specificity for every down-sampled dataset. Upward/downward sensitivity was outlined as appropriately figuring out an upward/downward pattern, whereas specificity was the flexibility to establish no pattern.


All strategies recognized growing, lowering, and steady developments of SARS-CoV-2 RNA concentrations in wastewater. The MK pattern take a look at and PC recognized upward developments ahead of RSI at first of Delta and BA.2/BA.5 waves. Specifically, the MK pattern take a look at recognized the growing pattern 17 and 12 days earlier than RSI initially of Delta and BA.2/BA.5 waves, respectively.

Likewise, PC recognized the growing pattern 16 and 26 days earlier than RSI at first of the Delta and BA.2/BA.5 waves, respectively. Moreover, the MK pattern take a look at and PC recognized the downward developments on the finish of the COVID-19 waves earlier than RSI. Within the down-sampling analyses, each the MK pattern take a look at and PC had poor (upward/downward) sensitivity for low sampling frequencies however improved with the rise in frequency.

The MK pattern take a look at attained acceptable upward/downward sensitivity with a minimal of 5 samples/week. However, PC reached acceptable upward/downward sensitivity with not less than 4 samples/week. Notably, specificity remained comparable and really excessive for each strategies in any respect sampling frequencies.


The MK pattern take a look at and PC supplied extra early warnings of upward and downward developments utilizing every day information than the RSI. Down-sampling analyses urged {that a} sampling frequency of not less than 4 and 5 samples per week was essential to establish developments utilizing PC and the MK pattern take a look at, respectively. Since PC required fewer samples/week than the MK pattern take a look at, WBE applications with funds constraints might want PC.

Total, the MK pattern take a look at and PC are inference-based strategies and can be utilized to categorise developments in an ordinary method. These pattern evaluation approaches could also be adopted by WBE applications to tell public well being departments on how COVID-19 case developments change, notably as the speed of scientific SARS-CoV-2 testing declines.

*Essential discover

medRxiv publishes preliminary scientific reviews that aren’t peer-reviewed and, subsequently, shouldn’t be considered conclusive, information scientific apply/health-related habits, or handled as established info.

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