Maine’s rural population may explain fluctuations in COVID-19 wastewater levels

Scientists at the Maine Center for Disease Control and Prevention hypothesize that levels of coronavirus found in wastewater collected in less densely populated parts of the state may fluctuate more than their more populous counterparts. But wastewater testing remains an important surveillance tool.

LEWISTON — Stark week-to-week fluctuations in the levels of coronavirus detected in wastewater collected from public sewer systems statewide, including in Lewiston-Auburn, might be related to Maine’s rural population, the Maine Center for Disease Control and Prevention said.

“Wastewater screening for COVID-19 is still quite new, so our scientists continue to explore reasons for the fluctuations,” Maine CDC spokesperson Robert Long said in an email Tuesday.

“One hypothesis is that wastewater systems in Maine tend to handle less volume than wastewater systems in more populous states,” he said.

As a result, fewer people with the virus can cause a larger spike compared to more populous areas.

In Portland, Maine’s most populous city, for instance, it would take a “really significant increase” in the prevalence of COVID-19 to cause trends to shoot upward, Michael Abbott, who runs the Maine CDC’s wastewater surveillance program, told the website FiveThirtyEight.

In other words, wastewater testing, much like other COVID-19 surveillance tools such as community transmission levels, is a game of numbers.

And in Maine – where the population density per square mile is smaller than four-fifths of the country – those numbers can be more challenging to interpret in rural parts of the state compared to more densely populated areas such as Cumberland County.

In rural parts of the state, wastewater surveillance data “tends to bounce up and down more rather than following a fairly smooth curve,” Abbott told FiveThirtyEight.

Still, wastewater testing remains an important tool of disease surveillance. Spikes in levels of coronavirus in wastewater can serve as a warning to public health experts and health care providers to prepare for an increase in cases.

A report published by the Maine CDC last Thursday showed that wastewater samples collected in Maine over the past six weeks had a higher virus concentration than every other state in the country except Vermont.

Following several weeks of downward hospitalizations in Maine, individuals hospitalized with COVID-19 on Tuesday represented a 33% increase compared to a week earlier, from 99 individuals on April 19 to 132.

Public health experts tend to consider hospitalizations a lagging indicator of a rise in cases.

In a Twitter thread posted Monday, Maine CDC Director Dr. Nirav Shah said that hospitalizations are rising across the state.

“And the majority are hospitalized for COVID, not with COVID,” Shah wrote, emphasizing “for,” meaning that the primary reason those patients were admitted was for symptoms related to COVID.

The omicron variant remains the driving force behind cases in Maine. As of the Maine CDC’s latest genome sequencing report published Monday, omicron and its subvariants represented 100% of the samples collected so far this month.