# Clinical correlation of SARS-CoV-2 wastewater passive sampling in long-term care facilities and wastewater treatment plants

## TL;DR

This study compares passive and composite sampling methods for detecting SARS-CoV-2 in wastewater from long-term care facilities and treatment plants, finding passive sampling to be effective and potentially more sensitive at low virus concentrations.

## Contribution

The study is the first to compare passive and composite sampling for SARS-CoV-2 detection in both long-term care facilities and wastewater treatment plants.

## Key findings

- Passive sampling performed similarly to composite sampling for SARS-CoV-2 detection and concentration.
- Passive sampling showed higher sensitivity at low SARS-CoV-2 concentrations (<180 gc/mL).
- Wastewater concentrations via passive sampling correlated with clinical cases, leading by 4 days on average.

## Abstract

Wastewater-based epidemiology (WBE) is a promising tool for improving health outcomes through early detection and cost-effective pathogen surveillance. Long-term care facilities (LTCFs) serve and employ vulnerable populations that may particularly benefit from the use of WBE, but financial and technical costs associated with standard sampling methods limit the feasibility of WBE in the LTCF setting. In this work, we used passive sampling to simplify the wastewater analysis process and compared its performance to the standard composite sampling method. Moore swabs and automatic composite samplers were used concurrently to sample wastewater from two LTCFs, and samples were analyzed for SARS-CoV-2 concentration. Passive sampling relies on an unknown volume of wastewater flowing through a cotton material, which complicates back calculations of pathogen concentration. We chose to calculate analyte concentrations based on the squeezed eluent from the cotton swab, which is practical for temporal analysis. Across all samples, passive and composite sampling performed similarly for SARS-CoV-2 detection and mean concentration. However, we observed a sensitivity advantage at low SARS-CoV-2 concentrations (<180 gc/mL) when using passive sampling. Furthermore, SARS-CoV-2 wastewater concentrations obtained via passive sampling correlated with the reported clinical cases, with wastewater concentration leading reported clinical cases by an average of 4 days. Passive and composite sampling were also performed at a wastewater treatment plant (WWTP) to examine the effects of facility type on sampling performance. To our knowledge, this is the first work performing a comparative analysis at both facility- and community-scale locations. Passive sampling yielded significantly higher SARS-CoV-2 and fecal load biomarkers than composite sampling at WWTPs, illustrating an important difference between LTCF samples and WWTP samples.