LEWISTON — Maine doctors reported a jump in patients with a fever and cough or sore throat this flu season, with a sharp rise in cases starting in December, opening the door to the possibility that COVID-19 was here months before the state’s first positive test on March 12.

Last year, the percentage of patients reporting symptoms of an influenza-like illness generally hovered around 1% or 2% and peaked at about 3%. This season, it began rising in December and climbed steadily to reach about 4% in January and about 5% in February. It peaked at 6.7% the week of March 15-21, just as the state was shutting down due to the pandemic.

An influenza-like illness, or ILI, can be caused by any number of viruses, including the flu. But numbers rose significantly across the country this season, leading some researches to look at whether ILI spikes were due to COVID-19, the pandemic virus whose symptoms can include fever, cough and sore throat.

In Maine, and across the country, the answer is unclear since widespread COVID-19 testing wasn’t available at the time.

“As far as COVID goes, it’s really hard to tell,” said Anna Krueger, state epidemiologist and influenza surveillance coordinator for the Maine Center for Disease Control.

About 55 health care providers, including all 33 Maine emergency rooms, report to the state when a patient comes in with a fever of 100 degrees or higher and a cough or sore throat — symptoms of an ILI. The data gives the CDC a look at how the flu season is shaping up since doctors aren’t required to report flu cases to the state.

It can be difficult to compare ILI data year to year since the number of reporting doctors may change. This year, for example, the CDC added two more emergency departments to its list of reporters.

But Maine’s ILI numbers were unusually high, even accounting for the two extra reporters. One factor: Maine’s flu season was particularly bad this season.

“It started off as a pretty significant season, so we did have quite a bit of outpatient visits that were attributed to this influenza-like illness. We had both influenza B and A circulating,” Krueger said. “That is probably a significant factor why both here in Maine and nationally we did see higher levels than in previous years for influenza-like illness.”

However, other flu seasons have been bad, too, and didn’t have the kind of ILI numbers Maine saw this year. Krueger cited the 2017-18 flu season as particularly bad as well, but CDC numbers from that time show ILI never rose to 2% — less than a third of this year’s peak. A Sun Journal analysis found the last highest peak was in 2014-15, and that was about 3.5%.

In June, researchers published a study in which they looked at this season’s national ILI surge and theorized it could have been affected by COVID-19. They estimated that more than 8 million Americans could have been infected with the virus in March, even though just over 100,000 had been officially documented at the time.

Maine CDC Spokesman Robert Long said the department would like to do some analysis of ILI and COVID-19 in Maine.

“We’re exploring the option of going back and looking at some early, early (COVID) test results. But right now we can’t speculate,” Long said. “It may also — may, I emphasize — involve looking at some antibody tests that have been done. But we’re not even at a point of knowing the efficacy of doing that at this point.”

Maine’s first official positive test came on March 12. Since then, there have been 3,500 probable and confirmed cases statewide, including 500 in Androscoggin County, 44 in Oxford County and 41 in Franklin County.