Most cases of foodborne illness are never reported to public health authorities. But that doesn’t mean those afflicted suffer in silence. Many people turn to social media to complain and even identify food purveyors they believe are responsible.

To tap into this rich source of information, city public health departments have begun mining the tweets and online reviews of those possibly sickened by food.

The City of Chicago Department of Public Health was the first to test the potential of social media in identifying foodborne outbreaks. The department partnered with civic-minded local technologists and the Smart Chicago Collaborative, a nonprofit organization that uses technology to improve the lives of Chicagoans, to develop an application to monitor Twitter for possible food poisoning references. A similar project is under way in New York, where the New York City Department of Health and Mental Hygiene is working with Columbia University technologists and the review website Yelp to comb restaurant patrons’ comments for signs of a budding outbreak.