Positive influenza tests surged in Maine last week as reported flu cases reached their highest levels since the H1N1 flu outbreak during the 2009-10 season, according to state data released Wednesday.

Maine has reported 682 positive flu tests so far, with 230 cases during the week ending Jan. 3 alone, according to the Maine Center for Disease Control and Prevention. An additional 157 cases were reported during the last full week of 2014.

Still, Maine and the New England states are seeing fewer cases per capita than much of the country, where the flu has hit hard in many areas this season. Twenty-one deaths have been recorded nationwide – none in Maine – and nearly 3,500 people have been hospitalized, according to the U.S. Centers for Disease Control and Prevention.

In Maine, there did not appear to be any concentrated outbreaks leading to school closings or nursing home quarantines. But Central Maine Medical Center in Lewiston diverted patients to other hospitals for two hours Monday evening because it had too many people with influenza or flu-like symptoms, officials reported.

In Brunswick, the Thornton Oaks Retirement Community curtailed some of its group activities because it had one confirmed case of the flu and a few other people staying home with flu-like symptoms. Officials there said the action was mostly preventive.

During the 2009-10 flu season, the Maine CDC reported 1,060 cases. In each of the four years between then and this season, cases topped out at less than 500. Because flu season is unpredictable and cases can peak at various times, it’s impossible to predict whether this season’s total will approach or surpass 2009-10, infectious disease experts say.

“Anything goes in the world of virology,” said Gwen Rogers, Maine Medical Center’s director of infection prevention.

Dr. Sheila Pinette, director of the Maine CDC, said one factor may be that the flu vaccine developed for this season is less effective than in previous years.

Unlike other vaccines, the flu vaccine may not work on all strains of the flu from season to season, according to the federal CDC. Scientists try to predict what strain will be circulating, but this year the vaccine did not closely match up against one of the most widely circulating strains, the agency said.

It’s still important to be inoculated, Pinette said, because the vaccine will work against three of the four known strains. And the federal CDC notes that vaccinated people who still contract the flu tend to have less severe symptoms than those who forgo the vaccine.

Pinette said the holiday season and winter weather may have contributed to the sudden spike in flu cases. The holidays bring people together, and the cold keeps people inside longer, she said.

At Thornton Oaks, Executive Director Don Kniseley said the retirement community hosts a vaccination clinic and closely monitors situations to make sure illness doesn’t spread.

“We try to be very proactive. Nearly everyone gets their flu shots,” said Kniseley, who expects the group activities will resume in the next couple of days.

At Maine Medical Center in Portland and MaineGeneral Medical Center in Augusta, typical numbers of flu hospitalizations are being reported for this time of year.

No cases have been recorded at the Portland Community Health Center, and the center is aggressive at vaccinating most people who come through the door, said Dr. Alison Gorman.

The center, which serves many low-income patients and the immigrant population, hosts two vaccination clinics. “We always have a real big push to get as many as we possibly can vaccinated,” Gorman said.

Rogers, at Maine Med, said the statewide increase in flu cases may only be on paper. The incidence of flu may actually be typical, but more cases get reported as an increasing number of patients ask to be tested, she said.

Rogers said more patients may be requesting flu tests because they want to obtain a prescription for Tamiflu, a drug that eases flu symptoms. She believes people are much more aware of the availability of drugs for flu treatment than they were a few years ago.

Rogers also said the flu is probably far more prevalent than the reported numbers because “typically, once flu is established in an area, doctors stop testing for it.” Also, some people with the flu never see a doctor and simply stay home until their symptoms subside and they recover.