By Ian Pepper, University of Arizona & WEST Center
Background: In Part 1, we described the concept of measuring Coronavirus concentrations in sewage as a leading indicator of the pandemic. Researchers at WEST have now been accepting and analyzing sewage samples from all over the U.S. including Los Angeles, Seattle and New York. The time frame for sampling has been from early March 2020 to June 2020, allowing for trends to be discerned when multiple samples over time have been analyzed.
A summary of data collected nationally from wastewater treatment plants (WWTPs) is shown in Table 1. Overall 26.6% of untreated wastewater samples tested positive for the virus. In contrast, no samples tested positive for Coronavirus after secondary treatment and disinfection. However, one
Non-disinfected secondary effluent was found to be positive for COVID-19. Meta data is now being collected for all communities served by each WWTP including the number of cases, and deaths on each day samples were collected. This data will be utilized in non-parametric models such as Kaplan Meir to aid in quantification of sewage viral concentrations as gene copies per liter.
Locally in Tucson Arizona, two samples per week have been taken from Agua Nueva WWTP, over the period of March – June 2020. Table 2 shows some viral concentration data as gene copies/liter. Note however, that we have additional samples that have been frozen and not yet analyzed due to the large number of incoming samples nationally. Trends that we have seen include an increase in viral concentrations from March to April, decreases in May, most likely due to social distancing and “Stay at Home” measures, and more recently in June, concentrations again increasing, most likely due to the re-opening. Currently, these data are being modelled.
Table 2. Viral concentration data.
Recently (June 20), the number of COVID-19 cases in Arizona and specifically Pima County (Tucson), are skyrocketing. In Pima County, over 1000 new cases were reported in 4 days (June 16-20), for an overall total of 5313 cases. This is reflected in sewage concentrations increasing from 6/2 to 6/11. In addition, a sample taken on 6/18 was positive for the N2 Coronavirus RNA target indicating significantly higher viral concentrations of 1.13 E06 and 297 new cases. These data illustrate that concentrations of virus in sewage is a leading indicator of COVID-19.