(CNN) -- An additional 10 states reported widespread seasonal flu activity last week, according to the Centers for Disease Control and Prevention.
The continued spread of the flu is expected in January. Typically, the flu season begins in the winter months and peaks in January or February, according to the CDC.
The number of states with widespread flu activity increased from 25 to 35 for the week ending January 4, according to the CDC's weekly flu advisory report.
"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 flu-like illnesses stayed the same from last week, at 20. The most severe activity was seen in parts of the South and Southwest.
Widespread flu activity was reported in Alabama, Alaska, Arkansas, California, Colorado, Connecticut, Georgia, Idaho, Illinois, Indiana, Kansas, Kentucky, Louisiana, Maine, Massachusetts, Minnesota, Missouri, Montana, Nebraska, New Hampshire, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Dakota, Texas, Utah, Virginia, Washington, Wisconsin and Wyoming.
In some areas, including central Texas and the San Francisco Bay Area, overflow tents have been set up to handle flu patients, CNN affiliates have reported.
Health officials have said this year's flu season appears pretty typical -- as opposed to last year's, which was severe.
The only atypical thing seen this year is that the most common strain has been H1N1, which became known as swine flu during a 2009 outbreak.
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," he 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, Jhung said.
Four new pediatric flu deaths were reported to the CDC last week, according to the flu report. A total of 10 influenza-related child deaths have been reported since September 29.
The agency does not track adult deaths related to the flu, although some states do, and deaths have been reported.
The exact number of flu-related adult deaths is hard to track and varies from year to year. The CDC has estimated that from 1976 through 2007, between 3,000 and 49,000 people died of flu-related causes.
"It depends on the season; it depends on the virus," Jhung said.
Last year, 381,000 people were hospitalized and 171 children died in what's being called a relatively severe season.
However, the CDC estimates that flu vaccination prevented 6.6 million illnesses last year, 3.2 million doctor visits and at least 79,000 hospitalizations.
Flu vaccines are recommended for everyone 6 months and older, especially pregnant women and those at high risk of complications, including the elderly, children younger than 5 years and those with underlying medical conditions such as asthma or diabetes.
Antiviral medications are a good treatment if you do get sick, Jhung said, particularly those at high risk for complications. Ideally, antivirals should be started within two days of when symptoms appear.