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Objective: To design and implement a tool that creates a secure, privacy preserving linkage of electronic health record (EHR) data across multiple sites in a large metropolitan area in the United States (Chicago, IL), for use in clinical research., Methods: The authors developed and distributed a software application that performs standardized data cleaning, preprocessing, and hashing of patient identifiers to remove all protected health information. The application creates seeded hash code combinations of patient identifiers using a Health Insurance Portability and Accountability Act compliant SHA-512 algorithm that minimizes re-identification risk. The authors subsequently linked individual records using a central honest broker with an algorithm that assigns weights to hash combinations in order to generate high specificity matches., Results: The software application successfully linked and de-duplicated 7 million records across 6 institutions, resulting in a cohort of 5 million unique records. Using a manually reconciled set of 11 292 patients as a gold standard, the software achieved a sensitivity of 96% and a specificity of 100%, with a majority of the missed matches accounted for by patients with both a missing social security number and last name change. Using 3 disease examples, it is demonstrated that the software can reduce duplication of patient records across sites by as much as 28%., Conclusions: Software that standardizes the assignment of a unique seeded hash identifier merged through an agreed upon third-party honest broker can enable large-scale secure linkage of EHR data for epidemiologic and public health research. The software algorithm can improve future epidemiologic research by providing more comprehensive data given that patients may make use of multiple healthcare systems., (© The Author 2015. Published by Oxford University Press on behalf of the American Medical Informatics Association. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

During the past decade, the incidence of certain bacterial pathogens that are commonly transmitted through food in the United States has decreased. Concurrently, the emergency department has become an increasingly common setting for health care. Because public health surveillance for bacterial foodborne diseases fundamentally depends on stool cultures, we conducted a survey of physicians who attended an emergency medicine conference to describe knowledge, attitudes, and practices among this provider population. A convenience sample of 162 physicians, representing 34 states, provided responses. Thirty-eight percent reported having ordered a stool culture for the most recent patient with acute diarrheal illness examined in the emergency department, but only 26% of the physicians subsequently received the stool culture results. For only 2 pathogens (Escherichia coli O157:H7 and Salmonella species) did at least one-half of the respondents provide the correct response regarding whether selected diarrheal disease pathogens were reportable in their state. Responses indicated familiarity with the Infectious Diseases Society of America's practice guidelines regarding stool cultures for patients with severe symptoms and a history of travel, but less so with characteristics of public health importance (i.e., attendance at day care and employment as a restaurant cook). We recommend that educational opportunities be made available to emergency care physicians that highlight the public health significance of acute diarrheal illness and that reinforce guidelines regarding culturing stool specimens, making recommendations to prevent further transmission, and reporting to local health authorities.