Building-level wastewater surveillance as an early warning system for COVID-19 outbreaks in congregate living settings

Abstract

The COVID-19 pandemic presented an opportunity to collect wastewater (WW) from a defined population of individuals within a building and monitor the sewage for viral RNA as a leading indicator of COVID-19 infections. The evaluation of the effectiveness of building-level WW surveillance programs as an early warning system has been limited by a lack of frequent asymptomatic surveillance of the defined residential population under WW surveillance. In this study we present the epidemiologic diagnostics of WW surveillance (sensitivity (Se), specificity (Sp), positive predictive value (PPV) and negative predictive value (NPV)) from university residence halls. WW surveillance was layered on top of a rigorous asymptomatic testing program (three times per week) and serves as the gold standard for comparison. This study also spanned across both the Spring 2021 semester when students were unvaccinated and the Fall 2021 semester when >95% of students were vaccinated for COVID-19 to understand how increased immunity may affect viral detection in WW. We analyzed composite WW samples from nine residential buildings that were collected twice weekly. The overall positive WW sample detection rate was 5.5% indicating the low-incidence context of this study population to allow for evaluation of WW surveillance as an early warning system. WW surveillance showed the best performance as a leading indicator of an infected individual when compared in a time inclusive of 1–2 days prior to the date of a clinical positive. The building-level WW surveillance sensitivity and specificity was found to be 60% and 94.9% (PPV: 47.4%; NPV: 96.9%), respectively in the Spring 2021; in the Fall 2021 sensitivity was reduced to 6.3% and specificity remained at a similar level of 97.5% (PPV: 14.3%; NPV: 94.1%). Combined for both semesters, the overall sensitivity and specificity were 32.3% and 96.4% (PPV: 38.5%; NPV: 95.3%). Convalescent shedding may explain up to 31% of false positive WW samples, contributing to decreased surveillance performance. This study demonstrates the greater effectiveness of building-level WW surveillance as an early warning system at the beginning of the COVID-19 pandemic when population-level immunity was naïve and fecal shedding of SARS-CoV-2 was likely more prevalent.