Reported flu cases continued to increase in Maine during the past week, but the number has yet to peak in a season that is already notable for its severity, health officials said.

The Maine Center for Disease Control and Prevention on Wednesday reported 531 new cases for the week ending Jan. 20, with 1,749 cases reported so far this flu season. The previous week there were 391 new cases.

Flu season runs from October through May, and nationally, the federal Centers for Disease Control and Prevention has reported widespread flu cases in every state except Hawaii. Nationally, there were 65,735 confirmed cases of influenza through Jan. 13, the most recent national data available, according to the U.S. CDC.

Maine has so far reported 22 deaths for which flu was at least a contributing factor, compared to 71 for all of 2016-17.

The flu strain is still predominantly influenza A H3N2, one of the most virulent strains, which more likely to require hospitalization, especially for seniors.

Maine reported 429 hospitalizations so far this season, and the mean age of those patients was 63. Twenty-five percent of all tested flu cases have resulted in hospitalization this season, compared to 14 percent in 2016-17.

Confirmed flu cases were most prevalent in York, Penobscot and Cumberland counties, with 394 cases in York, 257 in Penobscot and 253 in Cumberland County.

The actual number of flu cases is much higher than those reported because many people recover at home and are never tested. Symptoms include fever, chills, muscle aches, swollen lymph nodes, sore throat, headaches, fatigue and coughing.

There were 5,830 confirmed flu cases in Maine in 2016-17, although the predominant strain was less virulent, and there were fewer hospitalizations.

Places where people congregate – such as nursing homes, schools, universities and institutions, reported 52 outbreaks so far this season compared to 128 for all of the 2016-17 season. An outbreak is declared when three or more people at the same location report contracting the same infectious disease.

In nursing homes and assisted living facilities, which have a high percentage of immune system-compromised residents, the flu can spread quickly even though such facilities take precautions. Forty-six of the 52 outbreaks occurred in such facilities.

Richard Erb, president and CEO of the Maine Health Care Association, a trade group that represents nursing homes and assisted living facilities, said the facilities take standard precautions, such as encouraging flu shots for employees and patients, and encouraging visitors to come back on a different day if a flu outbreak is occurring. But he said there’s only so much that can be done.

“This is an especially difficult flu season,” Erb said. “Practically everyone in these facilities gets a flu shot.”

Erb said he heard from a manager of a nursing home who didn’t want to be publicly identified that had 24 cases of the flu.

Health experts say people should still get vaccinated if they haven’t yet done so, even though flu-shot clinics are typically held in the fall. The flu shot is available at primary care practices, drug stores and through some employers.

It’s still not clear how effective the flu vaccine is this year. Every year, scientists attempt to predict the predominant flu strains that will be circulated, and the vaccine is never 100 percent effective.

The vaccine was 48 percent effective in 2016-17 and 59 percent effective in 2015-16, according to the CDC.

Research shows that people who obtain vaccinations can still contract the flu, but it will most likely be a milder version.

Joe Lawlor can be contacted at 791-6376 or at:

jlawlor@pressherald.com

Twitter; @joelawlorph