Surveillance of SARS-CoV-2 in sewage from buildings housing residents with different vulnerability levels

Abstract

During the last three years, various restrictions have been set up to limit the transmission of the Coronavirus Disease (COVID-19). While these rules apply at a large scale (e.g., country-wide level) human-to-human transmission of the virus that causes COVID-19, the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), occurs at a small scale. Different preventive policies and testing protocols were implemented in buildings where COVID-19 poses a threat (e.g., elderly residences) or constitutes a disruptive force (e.g., schools). In this study, we sampled sewage from different buildings (a school, a university campus, a university residence, and an elderly residence) that host residents of different levels of vulnerability. Our main goal was to assess the agreement between the SARS-CoV-2 concentration in wastewater and the policies applied in these buildings. All buildings were sampled using passive samplers while 24 h composite samples were also collected from the elderly residence. Results showed that passive samplers performed comparably well to composite samples while being cost-effective to keep track of COVID-19 prevalence. In the elderly residence, the comparison of sampling protocols (passive vs. active) combined with the strict clinical testing allowed us to compare the sensitivities of the two methods. Active sampling was more sensitive than passive sampling, as the former was able to detect a COVID-19 prevalence of 0.4 %, compared to a prevalence of 2.2 % for passive sampling. The number of COVID-19-positive individuals was tracked clinically in all the monitored buildings. More frequent detection of SARS-CoV-2 in wastewater was observed in residential buildings than in non-residential buildings using passive samplers. In all buildings, sewage surveillance can be used to complement COVID-19 clinical testing regimes, as the detection of SARS-CoV-2 in wastewater remained positive even when no COVID-19-positive individuals were reported. Passive sampling is useful for building managers to adapt their COVID-19 mitigation policies.

Keywords: COVID-19; Wastewater surveillance, passive sampling; Wastewater-based epidemiology.

Graphical abstract

Fig. 1

Geometric Mean concentration of gene targets N1 and N2 (black bars, in log of GC·L⁻¹) and COVID-19 cases (shaded areas that are color-coded by subpopulation, see legend) in the elderly residence during the studied period (December 2021–March 2022). Inverted black triangles show the dates where both gene targets were below the limit of detection.

Fig. 2

Correlation between the reported cases and the geometric mean of the concentration of gene targets. Both variables were logarithmically transformed.

Fig. 3

Detection of N1 or N2 in the wastewater collected from the studied buildings using passive samplers for all cases except for the elderly residence where both active (ElderlyRes-W) and passive (ElderlyRes-T) sampling was used. Red cells indicate the dates where detection was positive and green cells when negative. The numbers inside the cells are the reported clinical cases in the corresponding building.