America's count of swine flu cases has risen to 21,449 cases and the number of deaths have nearly doubled to 87.
The continued spread signals the new strain of H1N1 flu is causing “something different” to happen in the United States this year — perhaps an extended year-round flu season that disproportionately hits young people, the Center for Disease Control and Prevention said.
The latest numbers, released Friday by the CDC is a jump from last week's count of 18,000 cases and 44 deaths.
Worldwide, the number of confirmed cases reached 44,287, the WHO reported Friday. WHO says cases increased by more than 10 percent in two days.
Figures provided by the global body show Argentina, Britain, Canada, Chile, China, Philippines and Thailand all reported a large rise in cases.
A total of 93 countries had reported cases to WHO by Friday.
In the U.S., Wisconsin, Illinois and Texas were the states with the most reported illnesses, and the Illinois count rose more than 500 since the last report. But CDC officials say much of the most recent flu activity has been in the Northeast. A quarter of the new deaths were in New York.
An unusually cool late spring may be helping keep the infection going in the U.S. Northeast, especially densely populated areas in New York and Massachusetts, the CDC officials said.
And infections among health care workers suggest that people are showing up at work sick — meaning that workplace policies may be contributing to its spread, officials reported.
The new strain of swine flu is officially a pandemic now, according to the World Health Organization. So far the virus is causing mild to moderate disease. The United States has been hardest hit, with upward of 100,000 likely unconfirmed cases and probably far more.
"The fact that we are seeing ongoing transmission now indicates that we are seeing something different," the CDC's Dr. Daniel Jernigan told a news briefing.
"And we believe that that may have to do with the complete lack of immunity to this particular virus among those that are most likely affected. And those are children," Jernigan added.
"The areas of the country that are most affected, some of them have very high population densities, like Boston and New York. So that may be a contributor as well. Plus the temperature in that part of the country is cooler, and we know that influenza appears to like the cooler times of the year for making transmission for effective."
Jernigan said in areas that are the most affected up to 7 percent of the population has influenza-like illness.
Summer of flu
"The United States will likely continue to see influenza activity through the summer, and at this point we're anticipating that we will see the novel H1N1 continue with activity probably all the way into our flu season in the fall and winter. The amount of activity we expect to be low, and then pick up later."
One worrying pattern: health care workers are being infected, and most reported they did little or nothing to protect themselves, the CDC's Dr. Mike Bell said.
People coming into emergency departments or clinics need to be checked right away for flu symptoms and anyone working with such a patient needs to wear a mask, gloves and eyewear, Bell said.
"We're beginning to see a pattern of health care personnel-to-health care personnel transmission in some of the clusters, which is also concerning, because it gets to the issue of people showing up to work sick," Bell said.
Doctors, nurses and technicians who have flu can spread it to vulnerable patients, Bell noted. At least 81 health care workers have been infected.