The COVID-19 pandemic has highlighted the potential role that wastewater-based epidemiology can play in assessing aggregate community health. However, efforts to translate Sars-CoV-2 gene copy numbers obtained from wastewater samples into meaningful community health indicators are nascent. This work measured Sars-CoV-2 nucleocapsid (N) genes (N1 and N2) weekly using reverse transcriptase droplet digital PCR from two municipal wastewater treatment plants for seven months. Four biomarkers (human mitochondrial gene NADH dehydrogenase subunit 5 (mit5), creatinine, ammonia, and biological oxygen demand (BOD)) were quantified and used to normalize Sars-CoV-2 gene copy numbers to account for variations in sewershed conditions. The normalized values were correlated to daily new case data and one-, two-, and three-week cumulative case data. N1 gene copies per day ranged from 3.9x109-4.5 x1011. Biomarker mass rates were determined for mit5 (3.4x109-1.3x1010 gene copies per day), creatinine (3.2x106-4.5 x1011 mg per day), ammonia (2.3x108-3.9x109 mg per day), and BOD (1.2x109-3.2 x109 mg per day). Mitochondrial and creatinine normalization methods showed the strongest correlations throughout the studying indicating that human-specific biomarkers were better at normalizing wastewater data than ammonia or BOD. The strongest correlations were observed with a one-day case data lag (ρ = 0.70). However, splitting the study into two time periods yields significantly stronger correlations. Early measurements were strongly correlated with a six-day case data lag (ρ = 0.83), while the latter half of the testing period yielded correlations of 0.81 with a one-day case data lag. For early stages of the pandemic, the wastewater samples may have indicated active COVID-19 cases before clinical indications. Wastewater-based epidemiology can be a tool to monitor community health, and human-specific biomarkers may be used to account for variations in sewershed conditions.

Normalization of wastewater SARS-CoV-2 gene copy numbers using readily available biomarkers to improve correlations with case data

ACS Fall 2021

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