Efforts to slow the spread of Covid-19 in the U.S have been stymied by the lack of an effective national surveillance system that can track the emergence of suspected and confirmed new cases in real-time. This is in part because important patient data is trapped in siloed electronic health record systems that don’t communicate well with each other; a new case of suspected Covid-19 in one health system could be invisible to another in the same community, blinding the systems and public health officials to Covid-19 hotspots that may be developing right in front of them.