If you ask the Centers for Disease Control and Prevention (CDC) in Atlanta, this year’s flu season is looking "moderately severe." That assessment has been reflected in the relatively calm tone of national media coverage in recent weeks.
But wait -- if you ask Google Flu Trends, we’re in the midst of an outbreak that is shaping up to be the most extensive on record. Never before this week have so many people searched for the terms that Google believes are likely indicators of the influenza virus. If Google’s algorithm is accurate, that should translate to a volume of doctor visits that significantly exceeds that of the H1N1 outbreak in October 2009. The media usually loves a good health scare. So why isn’t anyone sounding the alarm?
Because, four years after Google Flu Trends launched, the CDC still drives the bulk of national media coverage, suggesting that health reporters aren’t fully comfortable putting stock in Internet algorithms that go back only a few years. Yet Google’s figures may deserve far more attention than they’ve been getting.
By the CDC’s latest "outpatient surveillance" estimates, roughly 5.6 percent of Americans visiting the doctor are reporting respiratory illnesses, or flu-like symptoms. That’s a large number, significantly higher than the national baseline of 2.2 percent or the 2.3 percent peak of last year’s mild flu season. But it’s not entirely out of the ordinary.
But here’s the thing: The CDC’s current estimates aren’t all that current. Because they are based on after-the-fact reports from more than 3,000 health care providers around the country, the numbers can tell us only how many people were suffering from the flu a couple weeks ago. Today’s CDC FluView figures, for instance, come from the week of Dec. 23. We won’t know until Friday how many people visited the doctor with respiratory symptoms during the week that began on Dec. 30.
That’s where Google comes in. In fall 2008, the company’s charitable arm, Google.org, unveiled Flu Trends, a site that scans millions of Google searches from around the world to track flu activity in near real time. According to a study published in Nature in February 2009, the system can detect outbreaks nearly two weeks before they show up in the official CDC reports. And the site can tell you on any given day what countries, states and even cities are likely seeing the largest number of cases.
Today, Flu Trends is painting a foreboding picture. On a global scale of green (minimal flu activity) to bright red (intense flu activity), the United States is the reddest country in the world. Zoom in, and the red stretches are almost unbroken across the country’s eastern two-thirds. (Hang in there, Connecticut!) Boston, New York, Philadelphia, Houston and Denver are among a slew of cities tagged with the "intense" rating.
But the really ominous chart is the one that shows the trend line for the nation as a whole. It roughly agrees with the CDC that flu activity in December was about in line with the "moderately severe" peak in 2007-2008. But if Google is right, the CDC’s snapshot came just as the outbreak was gaining steam. Since mid-December, the trend line has rocketed past that of all previous years and now towers over that of the October 2009 H1N1 pinnacle, suggesting a CDC outpatient surveillance figure of an unprecedented 8.9 percent.
If that turns out to be accurate, the CDC’s Michael Jhung says this year’s would be the most widespread flu outbreak in decades. Jhung, a medical officer in the CDC’s influenza division, said he wouldn’t be shocked if that turns out to be the case, since his own models hint that the virus has not yet reached its peak. But he isn’t ready to go out on that limb just yet. "Is it going to be a more severe season than last year? I think without question," Jhung said. "Is it going to be a more severe season than a couple years ago, or the previous 10 years? We don’t know, and won’t know until the end of the season."
Perhaps not. But Google’s track record is disconcertingly impressive.
In the four years leading up to the Nature paper in 2009, its estimates lined up with the eventual CDC data with amazing accuracy. It seems almost certain that the most recent CDC figures are underestimating the outbreak’s current magnitude. Don’t be surprised to see a flurry of increasingly dire warnings and media reports in the weeks to come. The CDC’s Jhung recommends that everyone over the age of 6 who has not yet gotten a flu shot do so now. Even if you’ve already caught one strain, he said, there are still two others that the vaccine can protect against.