Swine flu means worst flu season in 12 years in U.S.

WASHINGTON (Reuters) - Swine flu is causing the worst flu season in the United States since 1997, when current measurements started, and has killed an estimated 3,900 people from April to October, U.S. health officials reported on Thursday.

Monitoring from 29 of 50 states shows 1,265 deaths since the pandemic of H1N1 influenza started in April, with 145 flu deaths among children, the U.S. Centers for Disease Control and Prevention said.

In the three months from August through October, 17,838 people have been hospitalized for and 672 people died from confirmed H1N1 in the states reporting to CDC, the agency said in its weekly report on death and disease.

The CDC was expected to give more details in a briefing later on Thursday, with possible new estimates of deaths from the virus.

"Nationwide, the percentage of visits to health-care providers for influenza-like illness was higher than that observed at the peak of any seasonal influenza season since ILINet (the CDC's reporting system) was implemented in its current form in 1997," the report reads.

In September and October the number of people hospitalized for flu was as high as usually seen by the end of an entire average flu season -- which runs from October through April in the United States.

The CDC said doctors need to treat cases of severe flu quickly with antiviral drugs such as Tamiflu, made by Roche AG, Relenza, made by GlasxoSmithKline or for severe hospitalized cases, peramivir, made by BioCryst.

(Reporting by Maggie Fox; Editing by Cynthia Osterman)