Pam Hetherly fills a syringe with COVID-19 vaccine at a clinic at the Augusta Armory, Dec. 21, 2021, in Augusta, Maine. Credit: Robert F. Bukaty / AP

Wastewater concentrations of COVID-19 in Maine’s most populous counties continued to increase last week, suggesting the virus is not letting up with hospitalizations surging.

The latest reports are concerning because wastewater is considered a leading indicator of cases. An uptick beginning in April preceded the hospitalization surge. The rise of concentrations in Maine’s large population centers suggests the virus situation could worsen.

Wastewater in York, Cumberland and Androscoggin counties show levels of COVID-19 at the highest they have been since early February, according to monitoring by the Maine Center for Disease Control and Prevention and Biobot. Aroostook County continued to report the highest levels in the state.

The rising levels come as daily COVID-19 hospitalizations in Maine have more than doubled in the past month, up to 219 as of Monday. The state also reported 38 patients in critical care and four on ventilators.

The seven-day case COVID-19 case rate in Maine has also continued to rise, although the official case rate likely represents an undercount in part because of increased use of at-home testing. Health officials have pointed to wastewater testing as a useful gauge of COVID-19 trends both in Maine and across the U.S. because it is not affected by individual testing levels.

Wastewater testing in Maine has shown rising levels of COVID-19 across most of the state since early April. Although levels have continued to rise in cities such as Lewiston and Portland, worsening trends across the U.S. mean those municipalities no longer rank as poorly compared to the national average of sites measured by Biobot as they did a few weeks ago.

The COVID-19 case rate nationwide is up 60 percent in the past two weeks, according to the New York Times, with every state reporting some increase over that time period.

An exception to the trend in Maine was Bangor, which had reported among the highest COVID-19 concentrations in the U.S. last month but has seen a drop in the past two weeks, state data show.