"The flu season is not over yet ... H1N1 has remained persistent in the southeast and now those states are experiencing more local and regional activity," U.S. Surgeon General Regina Benjamin told reporters in a conference call.
U.S. health officials said it was not clear why there were more swine flu cases in some regions and warned that many people were still vulnerable because they had not been immunized.
Alabama, South Carolina and Georgia have been reporting "regional disease" - one step below "widespread disease," Dr. Anne Schuchat of the U.S. Centers for Disease Control and Prevention said on the call. She said the situation in Georgia was unique.
"Recently, Georgia has seen more laboratory confirmed influenza hospitalizations each week than they've seen at any time since October," Schuchat said.
"They've had more than 40 hospitalizations in this past week, and for the third week in a row, Georgia had more hospitalizations than any other state in the country from laboratory-confirmed H1N1 influenza," Schuchat said.
Most of the people affected were adults with chronic health conditions and people who had not been immunized, Schuchat said. Georgia was among the states with the lowest rate of vaccinations, she said.
Benjamin again urged people to get immunized and said that the vaccine was in plentiful supply.
The U.S. supply of H1N1 vaccine reached 124 million doses last week, Benjamin said.
Swine flu has killed an estimated 12,000 Americans and put more than 265,000 into the hospital, according to CDC. It has largely displaced seasonal flu strains in the current flu season. Seasonal flu kills about 36,000 people in the United States each year and puts 200,000 in the hospital.
Swine flu emerged a year ago in the United States and Mexico and spread around the world in just six weeks, killing thousands of people. It hit children and young adults especially hard.
Although H1N1 activity has declined in the Americas and Europe, the World Health Organization says it is still technically causing a pandemic.