SIOUX FALLS, S.D. — Of this there is no doubt: The flu has sunk its teeth deep into South Dakotans. But a big, fresh spate of confirmed influenza cases doesn't necessarily mean the state's headed for a bad flu year, says the state's epidemiologist.

The state's latest weekly flu report added 420 new confirmed cases of influenza, a significant portion of the 1,103 confirmed infections tracked by the state so far this season. And a bulk of previously confirmed cases have been reported in recent weeks.

The spike makes it look as if the state is heading into the heart of flu season with the number of infections tracking ahead of previous years. But state epidemiologist Joshua Clayton said there's a twist this year: A more widely adopted type of rapid laboratory testing is contributing to the higher number of confirmed flu cases. So it's not fair to compare this year with those previous, he said.

"Everyone thinks it’s more of a severe year, and it’s more about that laboratory test change," Clayton said.

Rapid antigen tests, the older testing method for influenza, is increasingly being replaced in laboratories with more sensitive rapid molecular tests, he said.

"They’re becoming more and more used in clinics and hospitals, so the numbers from past years are not fully comparable" when looked at on a week by week basis, he said.

Clayton said he expects last year's number of confirmed cases — nearly 10,000 — to be something of the norm, potentially including this year. But this year's flu season severity will be hard to judge until it's over. South Dakota has likely not yet hit its peak week of the season. The peak week for flu cases in previous year has often been Feb. 1.

It's not too late for people to get a flu shot, Clayton said. The vaccination takes several weeks to become effective, but there's still plenty of flu season left if other years are any indication, he said.

"One of the most important things is get vaccinated," he said. "We’re still in that time were we’re increasing in activity and we’ll be at that high level for some time, and even though it does take a full two weeks to be protected once you get the influenza vaccine, it’ll have a lot of time to protect you moving forward."

So far this flu season in South Dakota, Influenza Type B has been the predominant type of flu in confirmed cases in South Dakota, according to state health officials. A total of 37 people have been hospitalized this season, according to data collected through Dec. 28. No deaths from the flu have been reported.