Discovering foodborne illness in online restaurant reviews.

Objective: We developed a system for the discovery of foodborne illness mentioned in online Yelp restaurant reviews using text classification. The system is used by the New York City Department of Health and Mental Hygiene (DOHMH) to monitor Yelp for foodborne illness complaints. Materials and Methods: We built classifiers for 2 tasks: (1) determining if a review indicated a person experiencing foodborne illness and (2) determining if a review indicated multiple people experiencing foodborne illness. We first developed a prototype classifier in 2012 for both tasks using a small labeled dataset. Over years of system deployment, DOHMH epidemiologists labeled 13 526 reviews selected by this classifier. We used these biased data and a sample of complementary reviews in a principled bias-adjusted training scheme to develop significantly improved classifiers. Finally, we performed an error analysis of the best resulting classifiers. Results: We found that logistic regression trained with bias-adjusted augmented data performed best for both classification tasks, with F1-scores of 87% and 66% for tasks 1 and 2, respectively. Discussion: Our error analysis revealed that the inability of our models to account for long phrases caused the most errors. Our bias-adjusted training scheme illustrates how to improve a classification system iteratively by exploiting available biased labeled data. Conclusions: Our system has been instrumental in the identification of 10 outbreaks and 8523 complaints of foodborne illness associated with New York City restaurants since July 2012. Our evaluation has identified strong classifiers for both tasks, whose deployment will allow DOHMH epidemiologists to more effectively monitor Yelp for foodborne illness investigations.