The three outbreaks involved a December 2012 meal in which a house salad caused seven out of nine people in a party to get sick; a January 2013 meal of shrimp and lobster cannelloni that sickened three of five people in a party; and a March 2013 meal of macaroni and cheese spring rolls that caused all six people in a party to get sick.
The outbreaks occurred due to problems like cross-contamination, bare-hand contact with ready-to-eat food, improper food storage and improperly sanitized work surfaces, the inspectors found.
The inspectors suspect these outbreaks likely sickened even more people than were identified. "We assume when we do outbreak investigations that there were other people who got sick we didn't know about," Balter said.
Balter did not find it discouraging that hundreds of complaints of illness on Yelp resulted in only a handful of confirmed outbreaks. She noted that of the 3,000 or so food-poisoning complaints received by the 311 service each year, only about 1 percent end up confirmed as a restaurant-related outbreak.
"In any surveillance system like this, there will be a lot of noise," she said. "The exciting thing for us is we could sort through that noise and find actual cases."
The New York City inspectors said they plan to continue using the software to scan for possible food-poisoning outbreaks. They will refine their methods by performing daily, instead of weekly, scans of Yelp reviews, and will expand the project to include other review sites.
Richard Hanley, an associate journalism professor at Quinnipiac University in Hamden, Conn., said, "Yelp is one of the emerging crowd-engaged tools health officials can use to track the emergence and spread of illnesses across geographical areas. Twitter, likewise, is a useful tool to pinpoint the onset of food-borne and other illnesses. All ought to be part of the surveillance toolkit," he added.