ESCANABA — The amount of the virus responsible for COVID-19 in Escanaba’s sewer system has dropped, but the area is still experiencing an above-average viral load.

According to the Sentinel Wastewater Epidemiology Evaluation Project, commonly known a “SWEEP,” the city’s most-recent wastewater sample, recorded Dec. 6, had more viral DNA than 65% of samples submitted to the program since Escanaba began tracking viral load through the project in late August of 2021.

SWEEP reports 15-day trends based on the exponential growth of viruses by categorizing both increases and decreases into percent ranges. The latest sample shifts the trajectory from a 1,000% or more increase in viral activity — the highest possible increase category reported by SWEEP — on Dec. 2, to a downward trend of -100% to -999%, the second to largest possible decrease category.

While the 15-day trends give a general picture of COVID-19 infections in Escanaba, there are delays in data reporting, and, by its nature, the system relies heavily on past data that may or may not be accurate.

For example, the samples submitted Nov. 8 and Nov. 15 had more viral DNA than 94% and 97% of all Escanaba samples, respectively. The Nov. 21 sample, however, was only reported as having a viral load greater than 6% of samples, with the following sample from Nov. 29 jumping back up to the 61st percentile.

While it is theoretically possible to have a 91% drop in viral load in a single week, it’s more likely there was an error in the data, which translated to a significant drop in the 15-day trend reported on Nov. 25 and then a rise in the trend reported for Dec. 2.

Still, it’s fair to say that the viral load in the city’s sewer system has dropped significantly from those November highs.

The viral load alone, however, doesn’t indicate in any way how sick individuals who contract COVID-19 are, as many people who are COVID-19-positive don’t show any symptoms. It’s also difficult to gauge how many people are actually infected because viral loads vary even among individuals and those who are sick are likely using home tests that aren’t reported to the state.

The highest viral load recorded through SWEEP for Escanaba was in late January of 2022, when just over 40 copies of the viral gene were detected per 100mL of wastewater for three samples — fractionally more than were detected last month. According to SWEEP, that 2022 spike in virus activity coincided with the highest number of cases reported for the city to the Michigan Department of Health and Human Services, with more than 350 cases per 100,000 people. Despite the nearly-identical viral load, only about 60 cases per 100,000 people were reported to MDHHS in November, which may be due to the shift to home testing.

By May of 2022 the number of cases reported to MDHHS dropped to levels below SWEEP’s reporting threshold and viral gene copies in wastewater dropped to some of the city’s lowest levels. If November’s spike mirrors 2022’s, the city could experience a period of relatively low infection through the holidays.

It is important to note, however, that 2022’s spike ended just as people were beginning to enjoy warmer weather and spend more time outside — naturally social distancing. Any downward trend could be negated by colder temperatures and holiday festivities opening up opportunities for people to gather indoors and spread the virus.