ESCANABA — The amount of detectable DNA from the virus responsible for COVID-19 has dropped in Escanaba’s sewer water, suggesting the city has recovered from a post-holiday spike in early January.

According to the Sentinel Wastewater Epidemiology Evaluation Project (SWEEP), a program that detects viral DNA in wastewater for a select group of sewersheds across the state, the last recorded sample from the Escanaba Wastewater Treatment Plant was in the 40th percentile for detectable DNA from the SARS-CoV-2 virus. To put it another way, three-fifths of all samples collected at the wastewater plant since Escanaba began participating in the program in August of 2021 have contained more of the virus responsible for COVID-19.

Looking at the individual samples submitted to SWEEP by the Escanaba Wastewater Plant, the negative trend is present but rocky. The 40th percentile sample, which was dated for Jan. 24, follows an 82nd percentile sample on Jan. 22 and a 63rd percentile sample on Jan. 17. However, it is important to note that all three of those sample followed a spike in viral DNA in early January that included a 90th percentile sample on Jan. 3 and a 98th percentile sample on Jan. 7.

The Jan. 24 sample also coincides with a drop off in cases of COVID-19 reported by the Michigan Department of Health and Human Services. The most recent data suggest that, based on a population of 100,000, only about 10 people in the sewershed area have tested positive for COVID-19 in a setting that requires state reporting — such as a hospital or nursing home. Anything below 10 persons per 100,000 people threshold is not reported by MDHHS due to privacy concerns.

While gauging infections against a hypothetical 100,000-person population allows for epidemiologists and other health officials to easily gauge infection rates across different sized communities, the numbers don’t translate well to communities the size of Escanaba. According to SWEEP, the Escanaba sewershed serves 12,600 people, and since there’s no such thing as a partial infection, 2 infections must be reported to the state in a seven-day period to be reportable by MDHHS.

At first glance, it would appear that the Escanaba data is a more precise estimate of active infections than, say, the Great Lakes Water Authority Oakland-Northwest-Wayne County Interceptor sewershed, which, with more than 840,000 people, stops publishing infection numbers when less than 85 people are reported as infected. However, larger communities typically have more access to healthcare services that would conduct the type of testing that is required to be reported.

Beyond the fact it is difficult to gauge what percentage of a population is exclusively relying on at-home test kits to determine if they are infected with COVID-19, many people who have the virus are asymptomatic and are never tested at all.

Still, the reported numbers from MDHHS have historically trended with spikes in DNA in the sewer water — even when professional testing was more prevalent.

A spike in viral activity in January of 2022 that included some of the highest concentrations of the virus found since the city began participating in SWEEP coincided with the highest number of cases reported by MDHHS for the city. While home tests were available in January of 2022, OSF St. Francis Hospital in Escanaba was still operating a drive-thru testing site that reported data to MDHHS. Even after that testing site closed in March of 2022, spikes and drops in MDHHS case reporting correlated with viral concentrations in Escanaba’s sewer water.

It is highly likely that more than two people in Escanaba are currently infected with the virus, but it is also a fair assumption that the number of COVID-19 cases have dropped significantly.

SWEEP’s own metric for trends, which is based on an exponential 15-day moving average, suggests that the amount of virus in the sewer system is trending downward at a rate of -100% to -999%.