Five more states reported widespread flu activity during the second week of January, according to the Centers for Disease Control and Prevention, bringing the total to 40 states.
Only 10 states are not yet reporting widespread activity: Alabama, Arizona, Florida, Hawaii, Iowa, Massachusetts, Mississippi, New Hampshire, South Carolina and Vermont.
"Widespread" means that more than 50% of geographic regions in a state -- counties, for example -- are reporting flu activity. The designation addresses the spread of the flu, not its severity.
However, the number of states experiencing a high proportion of outpatient visits to health care providers for flulike illnesses is 14 -- Alabama, Arkansas, Idaho, Kansas, Louisiana, Mississippi, Missouri, Nevada, New Mexico, Oklahoma, Oregon, Tennessee, Texas, and Virginia -- down from 20 in the previous week.
Ten children died from complications of the flu last week, bringing the pediatric death total for the season to 20. The CDC does not have data on the number of adult flu deaths. Experts estimate the number of flu-related deaths range from as low as 3,000 to as high as 49,000 people each year.
Typically, the flu season begins in the winter months and peaks in January or February, according to the CDC. But it's way too early to know if flu has peaked yet this year.
"As typical of a flu season, some areas are being harder hit than other areas," said CDC spokesman Tom Skinner.
One of those areas is California. Dr. Gil Chavez, deputy director for California's Center for Infectious Diseases, said 45 people under the age of 65 have died during the 2013-2014 flu season, which began in September. This includes two deaths in children.
"An additional 50 deaths are currently being investigated and are likely to be confirmed next week," Chavez said.
He said that a year ago, only five deaths had been reported at this time; there were only 106 flu deaths during the entire 2012-2013 flu season.
"H1N1 is the predominant virus circulating, and we do know when H1N1 predominates, there appears to be more fatalities," Chavez said. "We seem to have a predominance of a more deadly strain."
H1N1 is the same virus that caused a pandemic in 2009, Dr. Michael Jhung, a medical officer in the CDC's flu division, has said. It was dubbed swine flu because it was being seen for the first time in humans.
Since then, "it's established itself very nicely in the human population," Jhung said. H1N1 has been seen every season since 2009 in people and is no longer referred to as swine flu. The strain is so common that it was included in this year's vaccination, he said.
Adult flu deaths are not required to be reported to the CDC, but the government agency must be notified of any flu deaths in children. However, after H1N1 first surfaced, California health officials determined this was not enough.
Chavez said the lesson learned then was that "we needed a better way to determine the impact [of flu] on the community. So we in California made the decision to make deaths due to influenza in individuals under 65 mandatory to report."
What consumers need to know is that it's not too late to take steps to protect yourself from getting the flu, said Dr. Susan Rehm, medical director for the National Foundation for Infectious Diseases.
"People who are young and healthy should be aware that they may get the flu and it could be serious," Rehm said. One of the reasons people often say they don't get the flu vaccine is because they don't get sick. That excuse doesn't hold up, she said.
In addition to getting the vaccine, which can prevent flu -- or at least lessen symptoms, washing your hands frequently and staying home when you're sick can help you get through the flu season. Doctors recommend using antivirals within the first two days of experiencing any flulike symptoms.
CNN's Ashley Hayes contributed to this story.