Off the top of your head, can you think of a quick, simple, and anonymous way to report a food borne illness you may have contracted at a restaurant? And even if you can, have you ever done so? If not, you're not alone. In 2012, New York City's Department of Health and Mental Hygiene (DOHMH) found that residents weren't turning to the city's free 311 service to make such complaints, but rather they were reporting their experiences in Yelp reviews.

A study published on the CDC's website details the resulting 9-month collaboration between New York City's DOHMH, Yelp, and Columbia University "to explore the potential of using Yelp to identify unreported outbreaks." The study discovered 468 actionable complaints, 97 percent of which hadn't been officially reported to the city and analyzed roughly 294,000 Yelp restaurant reviews with three criteria in mind: descriptions of sickness (vomiting, diarrhea, etc.), multiple people being mentioned as ill, and a 10-hour-or-more lead before illness kicked in.

Further culling of the Yelp review data led to phone interviews with 27 complainants, most of whom had eaten questionable meals within 4 weeks of their interviews, which in turn identified three outbreaks meeting investigation criteria. Investigations of all three restaurants turned up a litany of nastiness: bare-handed food handling, cross-contamination, or even the presence of mice and cockroaches.

Those results could've been lengthier, but 102 Yelp reviewers who rang the DOHMH's alarm bells didn't accept phone interview requests—possibly because they could only be reached by Yelp's internal message service. The study noted the incredible divide between official reports and online-review complaints, and it concluded with recommendations for more public reporting options, from social-media campaigns like Utah's I Got Sick to Yelp and other review-aggregating sites offering official complaint info to users after a negative review is posted.