We have been able in HSRC to prototype one additional feature, which is a ''look-back'' function that facilitates very rapid outbreak investigations by providing access to electronic medical records to public health investigators as shown in Figure 6 . This feature requires a token that can be passed to a hospital information system that can uniquely identify a patient, and the reason we have prototyped this feature in the HSRC and not in RODS is simply that HSRC runs within the firewall so an unencrypted token can be used. The lookback is accomplished as follows: when a public health user identifies an anonymous patient record of interest (e.g., one of 20 patients with diarrhea today from one zip code), HSRC calls the UPMC Health System Web-based electronic medical record system and passes it the patient identifier. UPMC Health System then requests the user to log in using the UPMC-issued password before providing access to the record directly from its own secure Web site. This approach is not intended to be implemented in HSRC, but rather in the RODS system outside of the firewall of a health system. It is intended to use encrypted identifiers that the health system would decrypt to retrieve the correct record. The HSRC could provide the encryption-decryption service or it could be provided by another data system in the hospital. We estimate that the prevalence of health systems that have Web-based results review in the United States is 30% to 50% and growing so that this approach could very quickly improve the efficiency of outbreak investigations. For these reasons, we have moved to an application service provider model for dissemination in which we encourage state and local health departments to form coalitions to support shared services. We also have been fortunate to have sufficient grant funding from the Commonwealth of Pennsylvania to be able to support these services on an interim basis while sustainable funding models evolve.