However, it’s still not clear if tweet tracking will be as useful as analyzing search terms. For example, Google Flu engineers worked closely with the Centers for Disease Control and Prevention to make sure that their search-term tracking does indeed correlate with actual illness.

In general, Google Flu sees a rise in flu-related searches about two weeks before the CDC sees a rise in seasonal flu cases, because the federal agency generally relies on reports that must filter from patients to doctors and then to the CDC.

In fact, Google Flu could have picked up the swine flu cases early, as search terms jumped in Mexico before the rest of the world was aware that a new type of virus was emerging. Although Google Flu usually only posts data from the United States, they recently started to include data from Mexico.

As for the Twitter map, the researchers are working on validating that health-related comments—which for swine flu range from inane musings to truly useful information and local updates—actually mean something in the real world.

“If we know if a vaccine is coming out, and we can capture how people perceive this vaccine—they’re unhappy about it, they’re waiting for it, they’re suspicious about it—do those things match with what they do?” says Signorini. “If the public on Twitter is suspicious of the vaccine does it correspond to people actually not vaccinating their child with that vaccine?”

One problem is re-tweets, which are repostings of Twitter comments that people pick up from other Twitter feeds and include in their own, says Brent Csutoras, a social media consultant in San Mateo, Calif.

“The same news report might be re-tweeted and sent around 20,000 to 30,000 times and that would end up having an effect on this,” Csutoras says.

Despite the need for filtering re-tweets, Csutoras likes the map. “It’s very interesting,” he says. “I like the fact that you can see the conversation.”

He notes that other sites are more useful for people seeking information, such as the swine flu Google Map, because it shows verified swine flu cases. Other good sites to check out for swine flu online health information include HealthMap and SickCity, says Signorini. In addition, Mashable offers a good guide to following swine flu on Twitter.

Because of the re-tweeting and casual conversations on Twitter, the map is not currently that useful to individuals but could be helpful to public health officials, Csutoras says.

“It might be interesting to identify different cities where they could use Twitter as a means to communicate to people,” says Csutoras. “You might even say, hey we’re trying to get the word out in California, we can just Twitter it and the majority of people will find it. It might help agencies in some way.”

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