Indiana has seen 13 confirmed adult flu-related deaths since November 1, and two pediatric deaths, according to the state's health department.

Arkansas has seven confirmed flu fatalities. Many of the hospitals are at capacity because of the flu or other illnesses, state health spokesman Ed Barham said.

South Carolina has counted 22 flu-related deaths this season, compared with one for all of 2011, according to the South Carolina Department of Health. From September 30 through January 5, the state saw 1,084 influenza-related hospitalizations, the department said.

In Illinois, Department of Public Health Director Dr. LaMar Hasbrouck said Wednesday that since October, six flu-related deaths of patients in intensive-care units have occurred.

"We have been and continue to see an increase in flu activity across the state. The flu strain that is predominately circulating this year is typically more severe, with more hospitalizations and deaths," Hasbrouck said. "From the beginning of October through the end of December we've seen almost 150 people admitted to hospital intensive care units with influenza like illness.

"This compares to last year at this time when there were only two ICU hospitalizations and no deaths."

In Michigan, there have been four pediatric deaths related to the flu, said Angela Minicuci, public information officer for the Michigan Department of Community Health.

And the North Dakota Department of Health is reporting 1,077 cases of flu in the state as of Wednesday -- a sharp increase from the 625 cases reported last week.

Dr. David Zich, internal medicine and emergency medicine physician at Northwestern Memorial Hospital in Chicago, said this is the worst flu season he's seen in his 12 years at his hospital, in terms of the concentration of patients.

Northwestern Memorial Hospital is on "bypass," which happens when it is beyond capacity because of an influx of patients, such as during flu season.

That means advanced-life support ambulances with patients who are stable are referred to the next closest hospital, no more than five minutes away, Zich said, and transfers are not accepted from outside hospitals. For everyone else, they are open for business.

"The majority of flu patients are sent home, with very little else done, so we can handle that," he said.

Why so many cases?

Zich theorizes that one reason there are so many flu cases is that the heart of the flu season coincided with the December holiday season, meaning many people were already sleep-deprived from parties and were more likely to get sick.

Those who went to gatherings of family or friends may have already begun to feel sick, and spread the virus to others. People are generally contagious the day before symptoms start, and for five days after becoming sick, according to the Centers for Disease Control and Prevention.

Last flu season was light, but this year has brought with it some "ominous signs," Fauci of the NIH said Tuesday.

Flu cases started going up early, toward the end of November and the beginning of December, he said.

"And it went up on a pretty steep trajectory," he said. "The last time we saw that happen that way was the flu season of 2003 and 2004, which turned out to be a bad flu season."

The type of flu that is going around is called H3N2, which is often linked to more serious disease compared to other flu varieties, Fauci said.

But there's good news: That type of flu matches up well to the vaccine that is being distributed and given out throughout the United States.

People may get more complications from this particular strain of H3N2, "which may make them ill for a longer period of time," Dr. Michael Jhung, medical epidemiologist in the influenza division at CDC, told CNN's Mary Snow.

"But symptoms typically last up to seven days for a normal infection, a noncomplicated infection with influenza," he said. "And we usually see that from year to year regardless of what strains are circulating."

In a "light" year, a few thousand people may still die, but a particularly serious year could see up to 49,000 deaths from the flu, Fauci said. "There's an average of about 200,000 hospitalizations and there's a lot of economic burdens."

Protect yourself

If you haven't gotten an annual flu vaccine, it's not too late, doctors say. To further protect yourself, try to avoid anyone who is sneezing and coughing, and wash your hands. Also, exercise and eat healthy foods, Zich said.