ESCANABA — Escanaba is experiencing one of its largest spikes in COVID-19 cases in the last three years according to an unlikely source — sewage.

Changes in the way confirmed cases of COVID-19 are counted and reported have made it difficult to accurately gauge the number of infected people in any given area. At the start of the pandemic in 2020, most testing was done by medical professionals who submitted their test samples to laboratories, making it easy for epidemiologists and government officials to track infection trends. Now, the vast majority of infections are discovered through at-home testing kits with no real method or requirement for results to be reported.

While these changes have made it more difficult to know the number of people infected in a community, there are still procedures in place to know the general infection trend for an area. Perhaps the most accurate is data collected from the sewers.

The state of Michigan operates two separate wastewater monitoring programs that search for traces of the COVID-19 virus in sewage, the Sentinel Wastewater Epidemiology Evaluation Project (SWEEP) and the Michigan COVID-19 Wastewater Testing Dashboard, an older project launched in April of 2020 that shows longer-term trends and data based on the detection of individual genes from the virus.

The Escanaba Waste Water Treatment Plant is one of only two Upper Peninsula sites, the other being the Portage Lake Sewer Authority, that report in both systems. Other testing sites in all U.P. counties report exclusively on the Wastewater Testing Dashboard.

According to SWEEP, the most recent sample was in the 96th percentile for all samples collected at the Escanaba Wastewater Treatment Plant since collections started in August of 2020.

While it is difficult to compare average percentiles across different areas because each sewershed’s percentile is based only on data from its own testing, Escanaba currently has the highest percentile in the state. Other sewersheds seeing extremely high virus activity are the Saginaw Township Wastewater Treatment Plant (95th percentile) and the Portage Lake Waste Water Treatment Plant (89th percentile).

According to SWEEP data submitted on Nov. 8 and representing the last 15 days of testing, both Escanaba and the Portage Lake Sewer Authority have seen major spikes in the amount of COVID-19 DNA found in wastewater. SWEEP uses ranges to show the magnitude of a 15-day trend in any direction, but for both sewersheds the trend over the last 15 days has been a 1,000% or more increase — the highest range category in the SWEEP system.

Approximately 12,600 people live within the Escanaba sewershed’s area and traces of the virus have been detected for 19 weeks straight. A major increase in virus detection, however, began around Oct. 14, which started a string of three weeks straight that Escanaba was in the 1,000% or more increase category, based on 15-day averages. Around Nov. 4, there was a substantial dip in the amount of virus detected, suggesting cases were resolving and there were fewer infections.

However, by Nov. 11, when trend numbers were last calculated using the information submitted by the wastewater plant on Nov. 8, virus detection was once again increasing at the highest possible reporting rate.