Fortunately, the most troubling sign of a bad flu epidemic -- an unusual rise in deaths due to flu or pneumonia for a given time of year -- hasn't yet occurred.
But that may change in a hurry as the new flu continues its spread in communities across the U.S.
Last weekend, the H1N1 swine flu killed a 30-something Washington state man with an underlying heart condition. As of today, there are 3,300 probable and confirmed cases in 48 states and the District of Columbia, with 94 hospitalizations.
And that number is only the "tip of the iceberg," the CDC's Anne Schuchat, MD, said today at a news conference. The virus is spreading so widely, Schuchat said, that soon the U.S. will be unable to count individual cases.
"I believe the numbers we report are a minority of actual infections," Schuchat said. "The way we will be tracking in the future will be ... to put into context how much of the flu we are seeing is due to the new strain. That will be our priority in the fall, and during the flu season in the Southern Hemisphere, to see if this new virus is taking hold or just fizzling out or changing its properties."
What the CDC will track is flu trends. And the new flu is making an impact on these trends. Already, 2.6% of doctor visits are for flu-like illness, above the national baseline.
Not surprisingly, doctors have been sending a lot more samples to state labs for flu testing. That led to a big spike in confirmed flu cases in the week ending May 2, the most recent week in the CDC data.
That week, about 13% of flu tests were positive for flu:
- 33% of positive tests were either confirmed or probable type A H1N1 swine flu.
- 18% of positive tests were seasonal type A H1N1 virus.
- 16% of positive tests were seasonal type A H3N2 virus.
- 16% of positive tests were type A viruses not further subtyped.
- 17% of positive tests were type B flu bugs.
Those who do go to their doctor with flu-like symptoms won't have to wait for the test results. People who are seriously ill, or those with risk factors or underlying conditions that put them at risk of bad outcomes, will get treatment with Tamiflu or Relenza. Doctors will keep an eye on healthy people with mild symptoms but likely will not treat them with antiviral drugs, as most people recover fully from the new flu in a week or so.
Although the new flu bug is spreading quickly, the good news so far is that it remains a relatively mild flu bug. The key word here is "relative."
A new study of the new bug's spread in Mexico suggests that illness caused by the new bug is less severe than the illness caused by the bug that caused the 1918 flu pandemic and about the same as the flu bug that caused the 1957 pandemic.
The 1918 bug killed at least 675,000 people in the U.S. and up to 50 million people worldwide. The 1957 bug wasn't that bad -- but it killed 70,000 in the U.S. and up to 2 million people worldwide.
And, today the WHO said the new virus appears to be more contagious than seasonal flu virus.
There's still hope that the new H1N1 flu will fizzle out. But neither Schuchat and her CDC colleagues nor the World Health Organization is betting on that. The reason: The first wave of the 1918 flu was mild, too.