The current wave of swine flu may have peaked in most of the U.S., but the illness remains widespread and the threat of another wave remains, officials said. The news came as officials in Norway reported a mutation of the flu virus in two patients who died and one who became severely ill. The mutation, while seen before, appeared to make the H1N1 virus cause infection deeper in the respiratory system than the regular swine flu virus, a possible explanation for the more-severe cases, Norwegian scientists said. Swine flu cases appear to be declining in most of the U.S., the Centers for Disease Control and Prevention said. Flu activity is widespread in 43 states now, down from 46 last week, and 48 two weeks ago.