Where's the Flu? Get Ready

CDC Data Show Little U.S. Flu, but Google Flu Trends Shows Hot Spots

Medically Reviewed by Louise Chang, MD on December 28, 2011
From the WebMD Archives

Dec. 29, 2011 -- Where is this flu season we keep hearing about? Brace yourself.

Although it's seemed pretty quiet so far, flu season may already have arrived.

Although official CDC data show little flu activity throughout the U.S., it takes about two weeks to compile that data. More timely data from Google’s Flu Trends report is showing "moderate" flu activity in the U.S. overall, with about half of states still in the "low" category. But Kentucky and Nevada have "high" flu activity. So do several cities -- Atlanta, Boston, Chicago, Miami, and Washington, D.C. -- although Google Flu Trends for cities is still experimental.

Although the Google data are based on searches for flu information as opposed to actual cases, in recent years it's done a pretty good job of predicting what CDC will report. Also, the CDC provides a link to Google’s data off of its weekly flu report.

It may seem that flu season is getting a late start this year -- especially with the October peak of the 2009-2010 season -- but that's not the case. Last year, according to the CDC, flu activity started picking up in early January and peaked from mid-January to mid-February.

"The timing of flu circulation in the U.S. varies from year to year," Joseph Bresee, MD, chief of epidemiology and prevention at the CDC's Influenza Division, tells WebMD. "We often see little flu activity before January. We expect over the next few weeks to see it picking up."

CDC data from 1976 through 2011 show that 16 flu seasons peaked in February. Seven peaked in January, four peaked in December, four peaked in March, two peaked in April, and October and November each had one peak. (There was a "peak" in April 2009 due to the first wave of the flu pandemic, but that was outside the normal flu season).

There's only one thing that's for sure. "We always have a flu season," Bresee says.

Blunting the impact of the season is the record amount of flu vaccine available this year.More than 130 million doses of the vaccine were distributed in the U.S. by mid-December. It's not yet clear how many people actually got vaccinated, but Bresee is hopeful that increased use of the vaccine will make the season milder.

So far, the three flu strains covered by the seasonal flu vaccine are a good match for the flu strains circulating in the U.S.

New H3N2v Swine Flu Pops Up in 5 States

Not covered by the vaccine is the new H3N2v swine flu. The virus has been circulating among swine herds in the U.S. and probably elsewhere.

So far there have been 12 human infections with the virus. Six of the people infected caught the bug directly from live pigs, but six others -- including two unrelated children who attended the same day care in West Virginia -- had no recent exposure to pigs.

The bug has popped up in humans in five states: Indiana, Iowa, Maine, Pennsylvania, and West Virginia. Three of the patients were hospitalized. All fully recovered. There has been no sustained person-to-person spread of the virus, Bresee says, but the CDC is keeping close tabs on the situation.

That humans are catching the virus from pigs is ironic. Pigs got the parent H3N2 virus from humans in the early 1990s.

"Flu viruses circulating in swine occasionally infect humans,” says Bresee. “Usually they are one-off infections and go no further. Here it looks like there has been some person-to-person spread in at least two outbreaks, but we don't see sustained human spread."

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Joseph Bresee, MD, chief of epidemiology and prevention, CDC Influenza Division.

CDC: "FluView."

Google: "Google Flu Trends."

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