Swine flu cases fall across the U.S.

WASHINGTON – The level of swine flu activity in the United States appears to be declining, although officials are worried about another increase of cases during the Thanksgiving holiday when many people travel and families gather.

The number of states reporting widespread activity of the H1N1 virus dropped to 43 from 46 in the past week, and activity fell in all 10 regions of the country, according to the federal Centers for Disease Control and Prevention.

But flu cases are still rising in some states, including Maine and Hawaii, and it is too soon to know whether activity will surge again, said Anne Schuchat, director of the CDC’s Center for Immunization and Respiratory Diseases.

“Influenza is unpredictable, and it is so early in the year to have this much disease. We don’t know if these declines will persist, what the slope will be, whether we’ll have a long decline or it will start to go up again,” she said Friday.

The news came as scientists in Norway announced that they had detected a mutated form of the swine flu virus in two patients who died of the flu and in a third who was severely ill. It is the most recent report of mutations in the virus that is being watched closely for any change that could make it more dangerous.

In a statement, the Norwegian Institute of Public Health said the mutation “could possibly make the virus more prone to infect deeper in the airways and thus cause more severe disease,” such as pneumonia.

The institute said that there was no indication that the mutation would hinder the ability of the vaccine to protect people from becoming infected or impair the effectiveness of antiviral drugs in treating people who became infected.

Scientists have been analyzing the H1N1 virus from “a number of patients as part of the surveillance of the pandemic flu virus” and have detected several mutations, the statement said. While the existence of mutations is normal, and most “will probably have little or no importance … one mutation has caught special interest.”

The two patients who had the mutation and died were the first swine flu fatalities in Norway.

“Based on what we know so far, it seems that the mutated virus does not circulate in the population, but might be a result of spontaneous changes which have occurred in these three patients,” the statement said.