Brooke Jarvis / Special to The Washington Post

Twitter users send around 500 million tweets a day, an endless fire hose of information about how people feel, what they’re doing, what they know and where they are.

For epidemiologists and public health officials, it’s a potential gold mine of data — but only if they can figure out how to find the useful signal amid all that noise.

“The question is: How do you take these billions of messages, find the useful information and get it to people who can respond?” says Mark Dredze, an assistant professor of computer sciences at Johns Hopkins.

That’s a very big question, one whose difficulty has pushed many researchers away from the idea of using Twitter data, which they say is too messy and too uncontrolled compared with traditional methods of collecting health data, such as surveys and analyses of hospital visits. Others argue that, once we learn to effectively harness the data, Twitter’s very messiness (including the impulse to tweet what you had for breakfast or how annoying your runny nose is) will be what makes it an invaluable resource.

‘A pulse on the world’

“It’s like a pulse on the world, because people will just tweet whatever, whenever,” explains Christophe Girraud-Carrier, an associate professor of computer science at Brigham Young University, who studies what he and his colleagues have dubbed “computational health science.” “Poll answers are filtered by perception or memory; on Twitter, we’re actually observing real behavior” in real time.

Using Twitter data has other advantages, Dredze says. For starters, it’s faster: It can take the Centers for Disease Control and Prevention about two weeks to publish findings, Dredze says. Those numbers can additionally be delayed by the fact that a sickness doesn’t show up in statistics until someone goes to the hospital or does something else that causes the ailment to be reported.

Twitter, on the other hand, might reflect it the first morning someone wakes up with a sore throat. Speed can be a big advantage when tracking epidemics and emerging diseases, says Taha Kass-Hout, director of the CDC’s Division of Informatics Solutions and Operations. “An emerging disease from Southeast Asia can be in your backyard in 12 to 14, maybe 24 hours. So you have to respect that.”

Twitter can also provide a more detailed picture of where disease is breaking out, since many tweets are tagged with their locations. That, coupled with faster data, could help keep hospitals and clinics from getting overwhelmed in the middle of an outbreak: Even a few days’ notice that disease occurrences are spiking can mean being prepared with extra beds, staff or medicine. Detailed, location-specific data can also identify clumps of noncommunicable diseases — cardiovascular disease or Type II diabetes, for example — allowing health officials to focus education efforts in the areas that need it most.

Twitter is also in increasingly wide use, including in countries that don’t have effective public health tracking agencies. “In that case, anything Twitter can provide — whether it’s fast, slow whatever — is really valuable,” Dredze says.

Learning to be social

Those advantages, coupled with the fact that researchers are getting better at tracking and analyzing useful information, mean that “consensus is forming in the public health and health-care communities that we really need to pay attention to social media,” Kass-Hout says. However, he stresses that social media information is “a complementary tool, rather than a replacement” for more traditional methods of gathering information. It also depends on validation, the ability to prove that data collected through Twitter have real-world accuracy. That was one goal of Dredze’s research: to confirm the utility of Twitter data by studying if tweets about the flu could be filtered in such a way that they tracked with official flu rates.

Central to that effort is the signal-in-the-noise question, the effort to find and isolate useful information amid the barrage of tweets. In May 2011, Dredze and his colleagues were using a computer program to monitor mentions of the flu on Twitter. Suddenly, there was a massive spike in chatter. “It didn’t make any sense to us,” Dredze said. “The flu season was pretty much over.” They drilled down and discovered that people were discussing the fact that Kobe Bryant of the Los Angeles Lakers had played a game while sick.

That information may be interesting to basketball fans, but it’s not the kind of news that health researchers are looking for.

Dredze and his colleagues decided they needed a better algorithm, one that would allow the program to filter out tweets that aren’t actually about people having the flu. Their system starts by searching for some key words (such as “flu,” “fever” and certain brands of medicine) and screening out others (including “Bieber” with “fever” is a good sign that someone’s not talking about having the flu; so is including a URL, since it probably means they’re simply sharing an article), then applying grammatical analysis to figure out whether someone actually has the flu or is just talking about it. (Is “flu” the subject or the object of the verb? Which verbs are used? Which pronouns?)

They tested the system when reports of the latest flu epidemic hit the media in January. The number of tweets mentioning the flu shot up, though most of them didn’t reflect actual cases. But when Dredze and his team filtered tweets through their algorithm, they matched the CDC’s findings about actual flu rates.

Meanwhile, another key problem — underrepresentation of certain demographic groups, including the very young and the elderly — is diminishing rapidly as Twitter use expands, Kass-Hout says. Likewise, research is beginning to show that location data is indeed accurate enough to be of statistical use.