The health department got the idea for using Yelp after seeing chatter that helped with a monthlong restaurant investigation in 2011.
Officials reached out to Yelp, and the website agreed to help with a pilot project, said the health department's Dr. Sharon Balter. Crucial to their investigations is finding the people who get sick, and Yelp members have email accounts that can make that easier, she said.
Yelp sent the health department weekly roundups of restaurant reviews for nine months, beginning in mid-2012. Computer searches narrowed them to postings that mentioned someone getting sick. Investigators focused on illnesses that occurred between 12 and 36 hours after a meal -- the time frame for most symptoms of food poisoning to surface.
"Most people assume they got sick from the last place they ate," but that's not always the case, Balter said.
They also concentrated on clusters, not single cases. Other germs besides those in tainted meals can cause food poisoning symptoms like vomiting and diarrhea. Officials sent emails to 129 reviewers, but only 27 agreed to be interviewed.
Overall, three outbreaks involving 16 people were discovered from the Yelp reviews. The city identifies about 30 restaurant-based outbreaks in a typical year, Balter said.
The tainted food: house salads, shrimp and lobster cannelloni and a menu item called macaroni and cheese spring rolls.
Inspections at the restaurants found a variety of food safety violations in food storage and sanitation. Signs of mice and roaches were found at one.
Balter would not identify the three restaurants.
The pilot project was described in a report published online Thursday by the federal Centers for Disease Control and Prevention.
New York is continuing to monitor Yelp reviews, now with a daily report, and is exploring expanding to social media sites like Twitter, Balter said.
Georgia's Doyle noted that the project took a lot of work, and smaller places may not have the resources. The authors said restaurant review websites could boost reports by providing a link to local health departments.
Other places have been trying new approaches to catch cases. Last year, Utah launched an "I Got Sick" website to make reporting suspected food poisoning faster and easier. The Chicago Department of Public Health helped develop a system that contacts people who post complaints on Twitter.