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ESCANABA — The amount of detectable DNA from the virus responsible for COVID-19 in Escanaba’s wastewater has once again ticked upward, but the full effect of the holiday season is not yet known.

According to the Michigan Sentinel Wastewater Epidemiology Evaluation Project (SWEEP), the latest samples submitted by the Escanaba Wastewater Treatment Plant, contained more viral DNA than three-quarters of all samples submitted from the wastewater plant.

Samples are still lower than the record setting stretch from Nov. 6 through Nov. 27, 2023, which saw some of the highest viral load by SWEEP since Escanaba began participating in the program in August of 2021. But the samples from the week of Christmas — Dec. 20 and Dec. 25, 2023, which were in the 81st and 75th percentiles, respectively — are still significantly higher than the lows seen in late November and early-to-mid December, which averaged in the 67th percentile range and dipped as low as the 50th.

Based on SWEEP’s 15-day trends, the latest samples have broken a downward trend in viral concentration going back through December. When accounting for a sample that was likely recorded in error — a 6th percentile sample from Nov. 21 that was sandwiched between a 97th percentile sample on Nov. 20 and a 98th percentile sample on Nov. 27 — the string of negative-trending data goes back as far as Nov. 25.

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 some of 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. 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.

The number of infections reported to MDHHS in late December was just barely above the minimum reporting threshold of 10 cases per 100,000 people. If cases drop any lower, MDHHS won’t report infection statistics to protect the confidentiality of those individuals with infections.

Whether or not that will happen remains to be seen. With viral load in the city’s wastewater trending upwards and the 10-day incubation period of the virus delaying any holiday party exposures from becoming illnesses, it’s possible the number of infected people could rise rather than fall.