Maine recorded its highest single-day increase in COVID-19 cases Thursday, with daily case numbers and hospitalizations eclipsing even the worst period of the pandemic last winter.

While there are subtle signs that the current surge may be easing, the rapid spread of the delta variant across the region is straining the capacity of Maine hospitals and outpacing the state’s ability to review all positive cases as quickly as the reports are received.

The Maine Center for Disease Control and Prevention reported 925 cases of COVID-19 but no additional deaths on Thursday. It was the third straight daily report with more than 800 cases, although many of the cases were from the previous week. That’s because the recent surge in new infections has created a backlog of positive test results that must be reviewed by Maine CDC staff to separate new infections from follow-up tests.

Maine’s CDC has been struggling with backlogs throughout September, and the state had 2,500 cases still to be reviewed as of Wednesday. The backlog does not delay when a person is notified they have tested positive, but they have affected the state’s daily case reports and seven-day average. Cases that might have been reported a week or more ago are instead being added to reports this week.

Maine is one of a number of states that has been unable to keep up with positive tests during the pandemic. Alaska also has a large backlog of unreported cases as the delta variant surge continues there.

Alvaro J. Castro Rivadeneira, a researcher at the University of Massachusetts at Amherst who focuses on tracking and forecasting the coronavirus, said a review backlog could “absolutely” impact efforts to closely track what is happening with the coronavirus, although access to good data has been a constant challenge during the pandemic.

“Forecasts are based on the data available, so the more accurate and timely the data, the better the forecast,” he said.

Maine CDC Director Dr. Nirav Shah said the agency has reassigned or hired dozens of staff members – including 13 people added to the case review team in the past week – to help reduce the backlog. He said they are making progress, which appears to be reflected in the high daily case reports.

But Shah said the daily case rate is just one metric used to gauge how the virus is spreading in Maine, and that the positivity rate, which is the percentage of tests that come back positive, and hospitalization trends are crucial indicators.

“It doesn’t affect how we think about the pandemic, it doesn’t affect our positivity rates or anything like that,” he said.

BACKLOG HASN’T AFFECTED HOSPITALS

Hospitalization trends typically lag case trends and deaths are a “lagging indicator” to hospitalizations. But representatives of several hospitals in Maine said the review backlog has not impacted their operations.

“We are in a state of high transmission in our community and follow case rates, positivity rates and new cases,” Dr. Steven Diaz, chief medical officer at MaineGeneral in Augusta, said in a statement. “This backlog might have an impact as to the data being completely up to date, yet it really does not impact our ability to plan. We know we are in a significant wave of infectivity in our community and have this as an ongoing discussion.”

Northern Light Health, which operates Eastern Maine Medical Center in Bangor and other hospitals around the state, had a similar response.

“While being able to report all test results faster is ideal and a goal that the state and healthcare providers share, we are running more tests daily now than we have at any other time during the COVID-19 pandemic,” Northern Light spokesman Chris Facchini said in a statement. “The results and their trends still allow us to plan and prepare for what may be coming next.”

While the daily case reports have topped 800 each day this week, the number of positive test reports coming into the lab to be reviewed has declined from well over 600 a day last week to 550 a day this week, Shah said. That decrease combined with an increase in testing is seen as one potential sign that the delta-driven surge may be peaking in Maine, as it has in many other states.

Maine’s seven-day average of new cases stood at 590 on Tuesday, up from 456 cases daily for the week ending on Sept. 15. The highest seven-day averages of the pandemic occurred last January, topping 600 cases for a short period.

As a nation, the United States is currently averaging 227 new cases daily for every 100,000 residents over the past seven days. Maine’s rate of 291 cases for every 100,000 residents is the 15th highest rate in the nation and is higher than every other Northeastern and mid-Atlantic state except Delaware, according to data from the U.S. CDC. Connecticut’s seven-day average, by comparison, is 100 cases for every 100,000 residents.

DIFFICULT TO PREDICT TREND

Where Maine or other states are headed is difficult to predict amid the delta variant, however, public health officials and researchers say.

“So, the truth is we don’t know if the delta-driven surge has peaked, and Maine has one of the highest levels of uncertainty,” said Castro Rivadeneira, the University of Massachusetts researcher who is part of the team that produces the U.S. COVID-19 Forecast Hub.

The Forecast Hub serves as a central repository for forecasts and predictions from more than 50 research groups around the world whose predictions are used to create an “ensemble forecast.” Castro Rivadeneira said that because of the uncertainty the team recently switched to creating only one-week forecasts for cases and hospitalizations.

Castro Rivadeneira said another long-range forecasting group, the Scenario Modeling Hub, recently suggested an overall decline in cases in the U.S. headed deeper into the fall and into winter. But even that model found that in New England, in particular, the confidence intervals were so wide to the point that there was “too much uncertainty to say anything meaningful.”

Nicholas Reich, a UMass professor of biostatistics who helps lead the COVID-19 Forecast Hub from his lab, pointed to other research showing that Maine, New Hampshire and Vermont had some of the lowest infection rates in the country. In states with high infection rates, such as Florida, a higher percentage of residents could have a natural immunity than the population of northeastern states.

“But the fact that there has been a lot less COVID-19 in the Northeast so far, while of course a blessing in so many ways, also adds quite a bit of uncertainty now, because there is less immunity acquired from naturally occurring infections,” Reich wrote in an email. “Of course, vaccination rates are high in Maine and other New England states. This provides an important buffer.”

While case rates are rising here while declining elsewhere, Maine has among the lowest infection and death rates in the nation since the start of the pandemic. That has partly been attributed to Maine’s vaccination rate, which is the third-highest in the country after Vermont and Connecticut.

As of Wednesday evening, 73.4 percent of eligible Mainers had received the full slate of doses necessary for full inoculation against COVID-19. That figure drops to 64.9 percent when including children under 12 who are not yet eligible for vaccination.

Asked on Wednesday for his take on where Maine stands in the current surge, Shah said he was seeing “some signs of optimism on the horizon – but there are still a lot of signs of concern” about the pandemic. On the optimistic side, the “positivity rate” has fallen from more than 6 percent to 4.6 percent in the past two weeks while hospitalizations this week have been lower than Saturday’s peak.

“When you take all of that together there are some very early, way-too-preliminary, unclear signs that there might be an easing,” Shah said during a Wednesday briefing with the media. “But I’m not taking that to the bank yet.”

HOSPITALIZATIONS REMAIN HIGH

Hospitalizations were still hovering just below record levels on Thursday. There were 226 people hospitalized statewide with COVID-19 – down from a record 235 hospitalizations on Saturday – while 71 were in critical care and 28 were connected to ventilators.

While many Maine hospitals have seen their COVID-19 inpatient numbers level out after weeks of growth, MaineGeneral just experienced its worst burden of the entire pandemic. The Augusta hospital had an average of 18.3 confirmed COVID-19 inpatients each day for the week ending Thursday, up from 12.7 the week before and topping the worst week of the winter surge, 17.4 set in mid-December. Patient counts there climbed all week and hit 21 on Thursday, tying MaineGeneral’s high set Dec. 12-14.

A statewide vaccination mandate for hospital staff and many other health care workers takes effect Friday, although Gov. Janet Mills has said enforcement will be delayed until Oct. 29 to give workers more time to get their shots.

The mandate is being challenged in court, but a federal judge had not issued an order as of Thursday evening in a lawsuit seeking to block the mandate.

Workers can opt out for medical reasons only, and nine unnamed health care workers sued the state to demand a religious exemption as well. They argued the mandate violates their First Amendment rights because it unfairly singles out people who have religious objections and treats them less favorably than those who get the medical exemption.

The state said the state removed religious and philosophical exemptions to all vaccine requirements in order to protect people who cannot get those same shots for health reasons, so the rule serves a purpose that is allowed under the law.

Both sides made those arguments at a hearing last week.

Staff Writer Colin Woodard contributed to this report.