This article was produced by Kaiser Health News.When a Shigella outbreak at a San Jose, Calif. seafood restaurant sickened dozens of people last weekend, Yelp reviewers were on the case \u2013 right alongside public health officials.\u201cPLEASE DO NOT EAT HERE!!!!\u201d Pauline A. wrote in her Oct. 18 review of the Mariscos San Juan #3 restaurant. \u201cMy sister in and brother-in-law along with his parents ate here Friday night and all four of them ended up in the hospital with food poisoning!!!\u201dThat same day, the Santa Clara County Public Health Department shut down the restaurant. Two days later, officials announced that more than 80 people who had eaten there had become acutely ill, with many requiring hospitalization. Twelve diners went to intensive care units.Since then, the outbreak has grown to more than 90 cases in Santa Clara and Santa Cruz counties.Shigellosis is a contagious diarrheal disease caused by the Shigella group of bacteria and can be spread when people don\u2019t wash their hands after using the bathroom. More than500,000 cases are reported in the U.S. each year. The disease can cause severe dehydration or fainting and in rare cases may be fatal.Some health researchers and public health professionals believe consumer review sites like Yelp might just help them identify and investigate food poisoning outbreaks similar to this one. It\u2019s not unlike using Google searches to track potential flu and Dengue outbreaks.Santa Clara County epidemiologists currently aren\u2019t using Yelp in their Shigella investigation, and the reviewers apparently were not out ahead of public health officials in this case.But earlier research suggests that Yelp reviews may act as an early warning system or identify potential patients that public health officials might not otherwise have found in their food-borne illness investigations, especially if the reviewer did not seek medical care after falling ill.Public health workers in New York, aided by Columbia University researchers, scanned thousands of Yelp reviews in 2012 and 2013 to find previously undetected food-borne illness, unearthing nearly 900 cases that were worthy of further investigation by epidemiologists. Ultimately, the researchers found three previously unreported restaurant-related outbreaks linked to 16 illnesses that would have merited a public health investigation if officials had known of them at the time. Follow-up inspections of the restaurants found food-handling violations.In another study, researchers from Boston Children\u2019s Hospital analyzed more than 5,800 Yelp reviews of food services businesses near 29 colleges in 15 states, concluding that reviews describing food poisoning tracked closely with food-borne illness data maintained by the U.S. Centers for Disease Control and Prevention. The timeliness and often-graphic details of the reviews could prove useful for public health agencies investigating food poisoning outbreaks, the researchers concluded.Researchers also have examined Twitter and Facebook as possible food-borne illness surveillance tools, and Chicago\u2019s public health agency automatically sends information about its Foodborne Chicago reporting site to local Twitter users who complain of food poisoning.But Yelp\u2019s usefulness for epidemiologists is going to depend a lot on how it handles food poisoning complaints down the road.The company has been accused of approaching restaurants to remove negative reviews in exchange for advertising dollars, although a class action lawsuit on those grounds was dismissed.At the same time, Yelp is wrestling with how to handle reviews for businesses that become controversial overnight, serving as magnets for irate reviewers who have not patronized the business and just want to make a point.On Tuesday, the company placed an \u201cActive Cleanup Alert\u201d notice on Mariscos San Juan #3\u2019s review page noting that because the business \u201crecently made waves in the news,\u201d Yelp would \u201cremove both positive and negative posts that appear to be motivated more by the news coverage itself than the reviewer\u2019s personal consumer experience with the business.\u201dWhile some reviews were easily visible, others were segregated into Yelp\u2019s \u201cnot currently recommended\u201d category, which requires readers to click to see them and do not figure in the establishment\u2019s overall rating.That\u2019s where Andr\u00e9s Guerra\u2019s review was quarantined. From his hospital bed, the 27-year-old San Jose attorney wrote:\u201cOn Friday Oct 16th I ate the shrimp cocktail. I will spare the details, but I started being sick Friday night, then Saturday I was admitted to the ER and then the ICU. The Santa Clara County Public Health Department has already called me for their investigation \u2026 This restaurant put at least 11 people in the hospital I am at, and I\u2019m sure countless others elsewhere. I do not wish for a single other person to go through the hell I\u2019ve been through.\u201dReviews from five other people detailing how they fell ill were similarly hidden.After running a 104-degree fever and enduring days of vomiting, chills and diarrhea, \u201cI was like, what the hell?\u201d Guerra told Kaiser Health News while recuperating at home. \u201cI\u2019m not trying to slander any business \u2026 I just want no one else to go through this. I think Yelp could do a better job distinguishing between people who want to inform and those who want to attack.\u201dA Yelp spokeswoman noted that health scores for restaurants are currently provided in several selected counties or cities in California, Colorado, Kentucky, North Carolina and Illinois. In response to questions about food poisoning complaints, she referred a reporter to a general blog post, which says that the company tries not to \u201chighlight reviews written by users we don\u2019t know much about, or reviews that may be biased because they were solicited from family, friends, or favored customers.\u201dDoug Powell, a former professor of food safety at Kansas State University who now lives in Australia and writes for the BarfBlog food safety blog, regards Yelp and social media as potentially useful tools for public health investigators.\u201cBut it doesn\u2019t replace boots on the street, the epidemiological work that people have to do,\u201d he said. \u201cAll these things have to be taken with a grain of salt, because Yelp is a business.\u201dKaiser Health News is an editorially independent program of the Henry J. Kaiser Family Foundation, a nonprofit, nonpartisan health policy research and communication organization not affiliated with Kaiser Permanente.