Sewage testing indicates an uptick of Covid-19 presence on the island

Testing done one week ago
Tue, 07/28/2020 - 11:00am

The following was submitted by Wasterwater Plant Supt. Dylan Chase:

Chase added a caveat regarding these results: “I will warn again, the variation in viral shedding can be very different between each infected person, and depending on what stage of their illness they are in. Biobot stresses that the estimates are in ongoing Research & Development, so hold these estimates with caution.” 

When we received our next report, the concentration was higher at 20,368 parts per liter of sewage, with an estimation of 25 cases. A 24-hour composite sample was begun on July 19 at 7 a.m. and collected on July 20 at 7 a.m.

Estimated cases are based on the prevalence of a common virus found in human feces: pepper mild mottle virus (PMMV). Biobot Analytics, the Massachusetts-based company processing the tests, uses this as a fecal marker to normalize statistical deviation in the sample, and is used in conjunction with Washington County meta-data for population.   

Currently, (by reversing the math):

The WPCF treated 240,000 gallons, which equals 908,498.828 liters. Biobot is estimating that about 740,000,000 virus or genetic copies shed per day, per person.

According to the results, 908,499 liters multiplied by the 20,368 genetic copies found per liter results in 18,504,307,632 coming into the wastewater treatment plant per day.

By dividing the total amount of potential concentration of the virus captured during the sampling (18,504,307,632) by the virus shed per infected person per day (740,000,000), reaches a total of 25.01 infected people.