The city of Bangor's wastewater treatment plant on Main Street is pictured on July 28, 2014. Credit: Linda Coan O'Kresik / BDN

Wastewater testing shows a significant spike in COVID-19 in Bangor, with the city reporting among the highest virus concentrations among U.S. samples measured through the same testing method in the past six weeks.

COVID-19 levels in the wastewater in Maine’s third-largest city are still lower than they were in January and early February during the winter omicron spike. But the rise is another indication that the virus may again be on the rise in Maine, as the state’s top public health official warned last week. It comes as the more contagious “stealth omicron” variant has become the dominant strain here over the past month.

Most Maine counties have seen an increase in COVID-19 concentration in the wastewater the past two weeks, according to data from Biobot, a firm that tracks measurements in Maine and other states. That fits with a national trend. After dropping precipitously since late December, average effective virus concentrations in wastewater across the U.S. have picked up again in the past two weeks, Biobot data suggest.

But the Bangor area saw the most significant jump of Maine municipalities last week, with the effective concentration of virus in the wastewater nearly doubling to reach its highest level since early February.

The latest figures put Bangor in the 99th percentile in terms of all quantifiable samples in the U.S. over the past six weeks, according to Biobot. That reflects in part that COVID-19 conditions have been relatively good in much of the U.S. over that time period. Most Maine municipalities that were measured in early February saw higher concentrations than Bangor does now.

Other municipalities, including Portland, also reported rising COVID-19 wastewater concentrations last week. The jumps elsewhere were not as dramatic but still suggest much of Maine could be seeing greater transmission of the virus now that it was a few weeks ago. Health officials have pointed to wastewater testing as a useful indicator of COVID-19 spread as greater use of at-home tests has made statistics such as daily case counts less reliable.

Hospitalizations, another metric used to assess the prevalence of severe disease, have not yet shown a similar increase. Statewide, there were 97 patients hospitalized as of Monday. That figure has remained roughly flat over the past few weeks after falling dramatically for much of February and early March.