Epi-X is an internet-based secure website for the exchange of information regarding developing public health events. Reports are exchanged with state epidemiologists, state health officers and other key public health officials. Provisional and secure information is regularly posted on Epi-X. The Epi-X user base is restricted to public health officials at the local, state, federal and international levels. Private healthcare practitioners who do not otherwise hold a government position are not given access to Epi-X. As of August 2011, Epi-X has approximately 6000 users, of which approximately 1600 are authorized to directly contribute reports regarding developing public health events. Epi-X is frequently used to seek reports of cases of illness related to an outbreak, cluster or increased occurrence of a specific infectious disease. The usability and usefulness of Epi-X in this capacity have not previously been assessed.