“It was certainly a very vigorous flu season,” said Dr. Siiri Bennett, state epidemiologist at the Maine CDC. (Portland Press Herald photo illustration)

Maine suffered its worst influenza season in at least five years, with 9,018 cases reported in 2017-18, an increase of more than 50 percent from last season.

The flu season runs from October through late May, and the Maine Center for Disease Control & Prevention wrapped up its annual flu season weekly reports last week. The agency counted 1,750 hospitalizations to go with the 9,018 reported cases, surpassing the 5,830 cases in 2016-17.

Eighty-two people died in Maine from the flu, according to Maine CDC, compared to 71 the previous season.

Dr. Siiri Bennett, state epidemiologist at the Maine CDC, said it is difficult to compare flu seasons because different strains of the virus circulate and Maine’s reporting of cases improves every year. Bennett said some of the increase can be attributed to better reporting by doctor’s offices and health organizations, although there is no doubt that 2017-18 was a severe season.

“It was certainly a very vigorous flu season,” Bennett said.

Dr. Kolawole Bankole, director of the Portland Public Health Division, said the flu was “big time” this season.

Flu cases accelerated in December and peaked in February, before dropping off in mid-March and April. May began a steep decline in flu cases.

Flu is much more common than what is publicly reported because the data represents positive lab tests for influenza. Many more Mainers contract the flu but recover at home and are not tested.

The U.S. CDC also reported that this year’s flu season was severe nationwide, with widespread activity in all states, except Hawaii.

The early to middle of this year’s flu season was dominated by the H3N2 influenza A virus, a more-virulent strain of the flu that typically results in higher rates of hospitalization.

In January, about 25 percent of cases required patients to be hospitalized. But the second half of the flu season saw the emergence of influenza B and other flu strains that are usually milder versions. By the end of the season the hospitalization rate had declined to 19 percent of all cases. About 60 to 70 percent of all flu cases in Maine were influenza A H3N2.

Bennett said it is not uncommon for the predominant strain to change midway through the flu season.

“I’m not sure why, but there is frequently a shift partway through the season,” she said.

Nationally, the U.S. CDC reported 223,487 positive tests for the flu, with about two-thirds of the cases influenza A.

Also this season, the flu vaccine was 36 percent effective, according to the U.S. CDC, down from the previous two years. The vaccine was 48 percent effective in 2016-17 and 59 percent effective in 2015-16.

Bennett said the CDC “strongly recommends” vaccination, even in years when the vaccine is not as effective. The vaccine is never 100 percent effective because scientists, in order to get the vaccine to the market in time for flu season, must predict months beforehand those strains of the flu that will be most common.

“Even if a vaccine were only 25 percent effective, it would prevent many hospitalizations,” Bennett said. “If you can prevent a certain number of hospitalizations and deaths, it’s well worth it.”

For those who get a flu shot and still contract influenza, symptoms tend to be milder and not last as long, research has shown.

The National Institutes of Health reported in April that scientists are working on a new flu vaccine that would provide “broad protection against various influenza virus strains,” which would greatly improve vaccine effectiveness.

Symptoms include fever, chills, muscle aches, swollen lymph nodes, sore throat, headaches, fatigue and coughing. Along with immunizations, health-care providers say basic hygiene, such as frequent hand-washing; getting plenty of sleep; and staying away from sick people help prevent the spread of the flu.

Meanwhile, of the 141 outbreaks reported at institutions — an outbreak is defined as three or more cases at one location — 116 were at long-term care facilities, such as nursing homes.

“That’s the population most at risk,” Bennett said, “because often people are immune compromised, and as people get older, the body just doesn’t respond as efficiently to infections.”

The average age of a patient hospitalized for the flu this season was 60, according to Maine CDC data.

Bankole said Portland recognized the severity of the flu season this year and started a partnership with the Visiting Nurse Association to operate immunization clinics, including one at City Hall.

Those efforts will be improved and expanded for the next flu season, Bankole said. He added that the city also will work more with hospitals and the city’s homeless shelter to improve policies surrounding when people who are homeless become hospitalized with the flu.

Bankole said when a patient is homeless and discharged from the hospital after testing positive for the flu, Portland Public Health wants to make sure quarantine procedures at the homeless shelter are followed, when appropriate, because patients are often still contagious when they return to group living areas.