Health officials found three unreported outbreaks by sifting through nearly 300,000 reviews on the popular website. The outbreaks were small, together blamed for only 16 illnesses.
But one expert called it an innovative way to catch clusters of food poisoning.
''Great idea!'' said Mike Doyle, head of the University of Georgia's food safety center. ''Many people don't know how to contact the health department, but they're so familiar with social media.''
It's the latest example of using the Internet to track illnesses. Others have trolled Twitter, Facebook postings and Google searches in an attempt to monitor and predict ailments like the flu.
In New York, outbreaks were traced to three restaurants and inspectors found food handling problems at all three. Officials were also able to figure out the tainted food involved, but couldn't say exactly what germ in the food made people sick.
Traditionally, health officials hear about potential food poisonings from doctor reports and phone calls from people who say they got sick. In New York each year, about 3,000 people complain to the city's service hotline. Only about 1 percent of those calls pan out and lead to a cluster of illnesses.
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.
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.