Yelp Help

The power of Yelp reviewers should not be underestimated.

Unfavorable posts carry so much clout that a Virginia rug cleaner is even suing anonymous Yelpers for defamation, because the company claims negative comments caused a 30 percent drop in business.

Hundreds of Yelpers recently clobbered a Texas diner alleged to have banned two gay men from their restaurant.

Now, disappointed foodies are changing the way cities investigate outbreaks of food poisoning. New York City health officials found hundreds of unreported outbreaks during a recent pilot project by crunching the site's reviews, winnowing out keywords like "vomit" and "diarrhea," and contacting the users directly by email.

The results were alarming. Out of the 468 posts the team found about food sickness, only 3 percent of the cases had been reported via hotlines and other traditional means.

An Inside Yelper

Heather Hanson, a co-author of the study who works for the city's health department, said the team launched the pilot after stumbling on Yelp as a new source for investigations.

"One of our staff members, who is an avid Yelper, looked up the restaurant and noted that other patrons had been sick after visiting this restaurant," she said, "and they were people that we were not aware of through our investigation."

Since the reviews and contact information are public, Yelp happily gave the team a direct feed of reviews in the city.

Keywords helped to limit the data pool, but it's not a completely automated process. The researchers had to read through results to screen out entries with confusing slang, like: "bros, that bar was sick."

City officials contacted the reviewers, visited the restaurants, and were even able to track down sources of contamination, like bare-hand food handling and spoiled produce spawning disease in refrigerators.

The list of "patient zero" dishes included a house salad, macaroni and cheese spring rolls and lobster cannelloni.

Read More:

• Yelp Reviews Help Track Food Illnesses (New York Times)
• New York City Health Officials Are Using Yelp to Fight Foodborne Illnesses (Slate)
• Using Online Reviews By Restaurant Patrons To Identify Unreported Cases Of Foodborne Illness (CDC)