Monitoring population-level disease prevalence by measuring SARS-CoV2 in wastewater across a large geographical range

There is a need for wastewater based epidemiological (WBE) methods that integrate multiple,
variously sized surveillance sites across geographic areas. We developed a novel indexing method,
Melvin’s Index, that provides a normalized and standardized metric of wastewater pathogen load
for qPCR assays that is resilient to surveillance site variation. To demonstrate the utility of Melvin’s
Index, we used qRT-PCR to measure SARS-CoV-2 genomic RNA levels in influent wastewater from 19
municipal wastewater treatment facilities (WWTF’s) of varying sizes and served populations across the
state of Minnesota during the Summer of 2020. SARS-CoV-2 RNA was detected at each WWTF during
the 20-week sampling period at a mean concentration of 8.5 × 104
genome copies/L (range 3.2 × 102–
1.2 × 109
genome copies/L). Lag analysis of trends in Melvin’s Index values and clinical COVID-19
cases showed that increases in indexed wastewater SARS-CoV-2 levels precede new clinical cases by
15–17 days at the statewide level and by up to 25 days at the regional/county level. Melvin’s Index is
a reliable WBE method and can be applied to both WWTFs that serve a wide range of population sizes
and to large regions that are served by multiple WWTFs.