Although federal health officials decline to use the word “peaked,” the current wave of swine flu appears to have done so in the United States.
Flu activity is coming down in all regions of the country, the Centers for Disease Control and Prevention said Friday, though it is still rising in Hawaii, Maine and some isolated areas.
The World Health Organization said Friday that there were “early signs of a peak” in much of the United States.
On Wednesday, the American College Health Association, which surveys over 250 colleges with more than three million students, said new cases of flu had dropped in the week ending Nov. 13. It was the first drop since school resumed in the fall, and it was significant — new cases were down 27 percent from the week before.
And on Friday, Quest Diagnostics, the country’s largest laboratory, said its tests of 142,000 suspected flu specimens since May showed that the flu peaked in late October.
Nonetheless, Dr. Anne Schuchat, the director of immunization and respiratory diseases at the C.D.C., chose her words carefully, saying: “I wish I knew if we had hit the peak. Even if a peak has occurred, half the people who are going to get sick haven’t gotten sick yet.”
Dr. Schuchat also noted that even when new infections topped out, hospitalizations and deaths were still on the way up, because most took place days or weeks later.
Privately, federal health officials say they fear that if they concede the flu has peaked, Americans will become complacent and lose interest in being vaccinated, increasing the chances of another wave.
In New York, where cases peaked last May, vaccine clinics have gone begging for takers as long lines form in the rest of the country.
Epidemiologists expected a peak about now, because flu waves typically last six to eight weeks.
The current fall wave of new infections began in late August in the Southeast, where schools start earlier than on the East or West Coasts; it took several weeks to spread across the country and began falling in the Southeast two weeks ago.
The drop was clearly not caused by the swine flu vaccine drive, which has not gone as fast as the authorities had hoped because the vaccine seed strain grew so slowly.
Only about 54 million doses are available now, and Dr. Schuchat said she wanted to “apologize for the frustration the public has been experiencing.”
Lone Simonsen, an epidemiologist at George Washington University, said she expected a third wave in December or January, possibly beginning in the South again.
“If people think it’s going away, they can think again,” Dr. Simonsen said.
Based on death rates in New York City and in Scandinavia, she has argued that both 1918 and 1957 had mild summer waves followed by two stronger waves, one in fall and one in midwinter.
Only 43 states are now reporting “widespread” flu activity, down from 48 two weeks ago.
As Dr. Schuchat noted, that is still above peak activity in a typical flu season.
The winter flu season usually starts in December; it is expected to return this year.
Since last week, 21 children and teenagers died of confirmed or suspected cases of the flu, Dr. Schuchat said. Based on her agency’s belief that three pediatric deaths take place for each confirmed one, about 600 children and teenagers have died since this epidemic began.
The World Health Organization said the flu appeared to be peaking in the United States and some Western European countries, like Belgium, Britain and Ireland. But it was moving rapidly east and north.
Canada’s outbreak is still intensifying, as is the one in Norway, and Eastern Europe and Central Asia, including Afghanistan, are seeing a surge in cases.
Norway reported finding a mutated virus in three people who died or were severely ill. The mutation, known as D222G on the receptor binding domain, allow the virus to grow deeper in the lungs.
The mutation does not appear to be circulating and may have spontaneously arisen in the three patients, said Geir Stene-Larsen, director of the Norwegian Institute of Public Health. Only 3 of Norway’s 70 tested samples had it.
Asked about that, Dr. Schuchat said the same mutation had also been found in mild cases in several countries and it did not make the virus resistant to vaccine or to treatment with drugs like Tamiflu. She said that she did not want to “underplay” it, but that “it’s too soon to say what this will mean long term.”
The D222G mutation allows the virus to bind to receptors on cells lining the lungs, which are slightly different from those in the nose and throat.
Henry L. Niman, a flu tracker in Pittsburgh, has been warning for a week that the same mutation has repeatedly been found in Ukraine, which is in the grips of a severe outbreak and where surprising numbers of people have died with lung hemorrhages.
Separate reports of Tamiflu-resistant virus also surfaced Friday. Duke University Medical Center said it had found four cases among its patients in six weeks, and British health authorities reported five in one Welsh hospital.
Although Tamiflu resistance would be a serious worry for health officials, it was not clear that the strains were circulating outside the hospitals. Many isolated cases of resistant virus have been found.
